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Oligoasthenoteratozoospermia is an important factor affecting male fertility and has been found to be associated with genetic factors. However, there are still a proportion of oligoasthenoteratozoospermia cases that cannot be explained by known pathogenic genetic variants. Here, we perform genetic analyses and identify bi-allelic loss-of-function variants of MFSD6L from an oligoasthenoteratozoospermia-affected family. Mfsd6l knock-out male mice also present male subfertility with reduced sperm concentration, motility, and deformed acrosomes. Further mechanistic analyses reveal that MFSD6L, as an acrosome membrane protein, plays an important role in the formation of acrosome by interacting with the inner acrosomal membrane protein SPACA1. Moreover, poor embryonic development is consistently observed after intracytoplasmic sperm injection treatment using spermatozoa from the MFSD6L-deficient man and male mice. Collectively, our findings reveal that MFSD6L is required for the anchoring of sperm acrosome and head shaping. The deficiency of MFSD6L affects male fertility and causes oligoasthenoteratozoospermia in humans and mice., Competing Interests: Conflict of interest The authors declare no competing or financial interests., (Copyright © 2024 Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Ltd. All rights reserved.)

Reactive oxygen species (ROS) exert a vital role in sperm quality during semen preservation, where excessive ROS leads to oxidative damage and undermines sperm integrity. Curcumin, a botanical extract, is capable of neutralizing ROS and enhancing the activity of antioxidant enzymes. This study was aimed at evaluating the effects of curcumin on sperm viability, acrosome integrity, and antioxidant levels, as well as metabolomic and lipidomic profiles. The results demonstrated that curcumin at 25 µmol/L significantly enhanced sperm motility, plasma membrane, and acrosome integrity, elevated the levels of antioxidant enzymes (T-AOC, CAT, SOD), and decreased ROS production ( p < 0.05). Metabolomic analysis identified 93 distinct metabolites that showed significant differences between the control and curcumin-treated groups. KEGG pathways emphasized the participation of these metabolites in key metabolic processes such as the citric acid cycle, cholesterol metabolism, and fatty acid metabolism. Curcumin treatment brought about notable variations in lipid profiles, including increased levels of phosphatidylcholine, acylcarnitine, and triglyceride over the storage time, suggesting enhanced lipid anabolic activity. Overall, the supplementation of curcumin at 25 µmol/L effectively mitigates oxidative stress and prolongs the viability of semen storage at 16 °C by modulating specific metabolic and lipid profiles.

Transmembrane channel-like (TMC) proteins are a highly conserved ion channel family consisting of eight members (TMC1-TMC8) in mammals. TMC1/2 are components of the mechanotransduction channel in hair cells, and mutations of TMC1/2 cause deafness in humans and mice. However, the physiological roles of other TMC proteins remain largely unknown. Here, we show that Tmc7 is specifically expressed in the testis and that it is required for acrosome biogenesis during spermatogenesis. Tmc7 -/- mice exhibited abnormal sperm head, disorganized mitochondrial sheaths, and reduced number of elongating spermatids, similar to human oligo-astheno-teratozoospermia. We further demonstrate that TMC7 is colocalized with GM130 at the cis -Golgi region in round spermatids. TMC7 deficiency leads to aberrant Golgi morphology and impaired fusion of Golgi-derived vesicles to the developing acrosome. Moreover, upon loss of TMC7 intracellular ion homeostasis is impaired and ROS levels are increased, which in turn causes Golgi and endoplasmic reticulum stress. Taken together, these results suggest that TMC7 is required to maintain pH and ion homeostasis, which is needed for acrosome biogenesis. Our findings unveil a novel role for TMC7 in acrosome biogenesis during spermiogenesis., Competing Interests: JW, YY, LY, JQ, ZW, CQ, YG, GL, FG, ZC, XZ, HL, ZL No competing interests declared, (© 2024, Wang et al.)

C-terminal kinesin motor KIFC1 is increasingly concerned with an essential role in germ cell development. During the spermatogenesis of mice, rats, and crustaceans, KIFC1 functions in regulating meiotic chromosome separation, acrosome vesicle transportation, and nuclear morphology maintenance. The expression pattern of KIFC1 is conservatively concentrated at the acrosome and nucleus of haploid sperm cells. However, whether KIFC1 has similar functions in non-human primates remains unknown. In this study, we constructed the testis-specific cDNA library and cloned different transcripts of KIFC1 based on the genomic sequence. New variants of KIFC1 were identified, and showed different functional domains from the predicted isoforms. The spatio-temporal expression of KIFC1 proteins in seminiferous tubules of rhesus monkeys showed an obvious nuclear localization, specifically expressed in the spermatocytes and early haploid spermatids. The transcripts of KIFC1 also exhibited considerable expression in the nucleus of rhesus LLC-MK2 cells. Besides, we demonstrated that KIFC1 located at the acrosome and microtubule flagella of the mature sperm, and KIFC1 inhibition resulted in sperm tail deformation as well as increased the instability of head-to-tail connection. In summary, this study filled a gap in the reproductive research of the KIFC1 gene in non-human primates., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Infertility is a global health problem affecting one in six couples, with 50% of cases attributed to male infertility. Spermatozoa are male gametes, specialized cells that can be divided into two parts: the head and the flagellum. The head contains a vesicle called the acrosome that undergoes exocytosis and the flagellum is a motility apparatus that propels the spermatozoa forward and can be divided into two components, axonemes and accessory structures. For spermatozoa to fertilize oocytes, the acrosome and flagellum must be formed correctly. In this Review, we describe comprehensively how functional spermatozoa develop in mammals during spermiogenesis, including the formation of acrosomes, axonemes and accessory structures by focusing on analyses of mouse models., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Notch is a conserved cell-signaling pathway involved in spermatogenesis regulation. This study firstly evaluated the presence, localization patterns, acquisition origin and relation to acrosome reaction of Notch proteins in bull sperm. Western Blot analysis detected all Notch proteins in ejaculated bull sperm, and immunostaining described their specific sperm localization. Recovery of sperm from different segments showed that Notch proteins have testicular origin (NOTCH1, NOTCH2, DLL4), are sequentially acquired during sperm maturation along epididymal transit (NOTCH3, DLL3, JAGGED1-2), or post-ejaculation (DLL1, NOTCH4). Testis NOTCH2 is ubiquitously expressed in all germ-cell lines, whereas DLL4 is expressed in round and elongated spermatids during the Golgi, Cap, Acrosome and Maturation phases. In vitro spontaneous and induced sperm acrosome reaction induce consistent sperm regional relocation of NOTCH2, DLL4 and JAGGED1, and these relocation patterns are significantly associated to sperm acrosome status. NOTCH2 and JAGGED1 are relocated from the head apical to the post-equatorial regions, whereas DLL4 is lost along with the acrosome, evidencing that sperm spatial redistribution of NOTCH2 and JAGGED1 is linked to acrosome reaction onset, whereas DLL4 loss is linked to AR completion. Overall, results prompt for a relevant Notch role in bull sperm acrosome testicular development, epididymal maturation and acrosome reaction., (© 2024. The Author(s).)

Sperm heads contain not only the nucleus but also the acrosome which is a distinctive cap-like structure located anterior to the nucleus and is derived from the Golgi apparatus. The Golgi Associated RAB2 Interactors (GARINs; also known as FAM71) protein family shows predominant expression in the testis and all possess a RAB2-binding domain which confers binding affinity to RAB2, a small GTPase that is responsible for membrane transport and vesicle trafficking. Our previous study showed that GARIN1A and GARIN1B are important for acrosome biogenesis and that GARIN1B is indispensable for male fertility in mice. Here, we generated KO mice of other Garins, namely Garin2, Garin3, Garin4, Garin5a, and Garin5b (Garin2-5b). Using computer-assisted morphological analysis, we found that the loss of each Garin2-5b resulted in aberrant sperm head morphogenesis. While the fertilities of Garin2-/- and Garin4-/- males are normal, Garin5a-/- and Garin5b-/- males are subfertile, and Garin3-/- males are infertile. Further analysis revealed that Garin3-/- males exhibited abnormal acrosomal morphology, but not as severely as Garin1b-/- males; instead, the amounts of membrane proteins, particularly ADAM family proteins, decreased in Garin3 KO spermatozoa. Moreover, only Garin4 KO mice exhibit vacuoles in the sperm head. These results indicate that GARINs assure correct head morphogenesis and some members of the GARIN family function distinctively in male fertility., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Reproductive failure in dogs is often due to unknown causes, and correct diagnosis and treatment are not always achieved. This condition is associated with various congenital and acquired etiologies that develop inflammatory processes, causing an increase in the number of leukocytes within the female reproductive tract (FRT). An encounter between polymorphonuclear neutrophils (PMNs) and infectious agents or inflammation in the FRT could trigger neutrophil extracellular traps (NETs), which are associated with significantly decreased motility and damage to sperm functional parameters in other species, including humans. This study describes the interaction between canine PMNs and spermatozoa and characterizes the release of NETs, in addition to evaluating the consequences of these structures on canine sperm function. To identify and visualize NETs, May-Grünwald Giemsa staining and immunofluorescence for neutrophil elastase (NE) were performed on canine semen samples and sperm/PMN co-cultures. Sperm viability was assessed using SYBR/PI and acrosome integrity was assessed using PNA-FITC/PI by flow cytometry. The results demonstrate NETs release in native semen samples and PMN/sperm co-cultures. In addition, NETs negatively affect canine sperm function parameters. This is the first report on the ability of NETs to efficiently entrap canine spermatozoa, and to provide additional data on the adverse effects of NETs on male gametes. Therefore, NETs formation should be considered in future studies of canine reproductive failure, as these extracellular fibers and NET-derived pro-inflammatory capacities will impede proper oocyte fertilization and embryo implantation. These data will serve as a basis to explain certain reproductive failures of dogs and provide new information about triggers and molecules involved in adverse effects of NETosis for domestic pet animals.

Semen freezing and storing has been widely used in reproductive biotechnology, being applied to certain males of livestock breeds or animal species with economic value such as the Angora goat. The development of a semen extender with the cryoprotective agents can prevent the deterioration of sperm parameters after thawing. This study aimed to investigate lipid mixtures (from a liposome kit, Lps) and melatonin (Mel) at different doses to prevent the deterioration of sperm parameters and to provide the cryoprotective effects on sperm DNA. The Angora goat ejaculates were collected and pooled. They were divided into seven equal volumes, and each of them was diluted with the extenders of the experimental groups with additives (Lps 321.99 μg/mL, Lps 841.33 μg/mL, Mel 0.25 mM, Mel 1 mM, Lps 321.99 μg/mL + Mel 1 mM, Lps 841.33 μg/mL + Mel 0.25 mM) and no additives (control group). After the freeze-thawing process, motility, viability, acrosome integrity, DNA double-strand breaks, and abnormal DNA integrity were assessed for different extender groups. It was determined that the use of Lps alone at low dose or the combination of Lps and Mel had significant cryoprotective effects on motility, viability, acrosome integrity, and DNA damage in Angora goat sperm. This study will help us to understand the effects of Lps and Mel used alone or in combination at different doses and which doses give the optimum spermatological parameter rates following the freeze-thawing process, and hence it will shed light on further studies., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2024 Society for Cryobiology. Published by Elsevier Inc. All rights reserved.)

Thoroughbred stallions that carry a double-homozygous genotype A/A-A/A for SNPs rs397316122 and rs69101140 in exon 5 of the FKBP6 gene (chr13; EquCab3.0) are uniquely subfertile due to impaired acrosomal exocytosis (IAE). In this study, the sperm proteome in frozen/thawed semen from subfertile Thoroughbred stallions was studied and compared to that of frozen/thawed sperm from fertile Thoroughbred stallions. A total of 2,220 proteins was identified, of which 140 proteins were found to be differentially abundant in sperm from the subfertile stallions compared to that of fertile stallions (83 less and 57 more abundant). Proteins of differential abundance in sperm from the subfertile stallions were mainly overrepresented in the "metabolism" and the "metabolism of lipids" pathways. One of these proteins, arylsulfatase F (ARSF), was studied by immunofluorescence. A lower proportion of sperm displaying ARSF signal at the acrosome region was observed in sperm from subfertile Thoroughbred stallions. In addition, heterologous zona pellucida binding assays revealed that sperm from subfertile Thoroughbred stallions bound at a lower proportion to zonae pellucidae than sperm from fertile Thoroughbred stallions. In conclusion, a group of differential abundance proteins, including some of acrosome origin, were identified in sperm from subfertile stallions with acrosome dysfunction., (© 2024. The Author(s).)

As in most cells, intracellular pH regulation is fundamental for sperm physiology. Key sperm functions like swimming, maturation, and a unique exocytotic process, the acrosome reaction, necessary for gamete fusion, are deeply influenced by pH. Sperm pH regulation, both intracellularly and within organelles such as the acrosome, requires a coordinated interplay of various transporters and channels, ensuring that this cell is primed for fertilization. Consistent with the pivotal importance of pH regulation in mammalian sperm physiology, several of its unique transporters are dependent on cytosolic pH. Examples include the Ca 2+ channel CatSper and the K + channel Slo3. The absence of these channels leads to male infertility. This review outlines the main transport elements involved in pH regulation, including cytosolic and acrosomal pH, that participate in these complex functions. We present a glimpse of how these transporters are regulated and how distinct sets of them are orchestrated to allow sperm to fertilize the egg. Much research is needed to begin to envision the complete set of players and the choreography of how cytosolic and organellar pH are regulated in each sperm function.

BACKGROUND Cryopreservation preserves male fertility, crucial in oncology, advanced age, and infertility. However, it damages sperm motility, membrane, and DNA. Zinc (Zn), an antioxidant, shows promise in improving sperm quality after thawing, highlighting its potential as a cryoprotectant in reproductive medicine. MATERIAL AND METHODS Gradient concentration of ZnSO₄ (0, 12.5, 25, 50, and 100 &micro;M) was added in the Glycerol-egg yolk-citrate (GEYC) cryopreservative medium as an extender. Alterations in sperm viability and motility parameters after cryopreservation were detected in each group. Sperm plasma membrane integrity (PMI), acrosome integrity (ACR), DNA fragment index (DFI), and changes in sperm mitochondrial function were examined, including: mitochondrial potential (MMP), sperm reactive oxygen species (ROS), and sperm ATP. RESULTS We found that 50 &micro;M ZnSO₄ was the most effective for the curvilinear velocity (VCL) and the average path velocity (VAP) of sperm after cryo-resuscitation. Compared to the Zn-free group, sperm plasma membrane integrity (PMI) was increased, DNA fragmentation index (DFI) was decreased, reactive oxygen species (ROS) was reduced, and mitochondrial membrane potential (MMP) was increased after cryorevival in the presence of 50 &micro;M ZnSO₄. CONCLUSIONS Zn ion is one of the antioxidants in the cell. The results of our current clinical study are sufficient to demonstrate that Zn can improve preserves sperm quality during cryopreservation when added to GEYC. The addition of 50 &micro;M ZnSO₄ increased curve velocity, mean path velocity, sperm survival (or plasma membrane integrity), and mitochondrial membrane potential while reducing ROS production and DNA breaks compared to GEYC thawed without ZnSO₄.

Low acrosin activity (LAA) is associated with sperm function anomaly and poor outcomes of in vitro fertilization. In this study, we confirm that 993 semen samples with LAA had a reduced sperm motility and low in vitro fertilization rate in comparison with 1332 normal controls (NC). Proteomic comparison between 11 LAA and 11 NC sperm samples identified 35 upregulated and 99 downregulated proteins in the LAA group. Indeed, proteomic data showed that acrosome enzymes Spam1 and Acrosin were among the downregulated proteins in the LAA group, which was validated by quantitative PCR and immunefluorescent staining of sperm cells. The KEEG pathway analysis revealed a deficiency of GSH and Gln biosynthesis in LAA sperm cells. Immunofluorescent staining of sperms and quantitative PCR verified downregulation of GLUL and GCLC, the key enzymes for GSH and Gln biosynthesis. Moreover, the results of ELISA assay confirmed low levels of GSH and Gln in LAA sperm cells. Mechanistic studies showed that addition of 10 mM H 2 O 2 to semen samples led to a significant reduction of acrosin activity and sperm motility, most possibly by triggering premature acrosome release. In contrast, the presence of 20 mM GSH blocked the oxidative effects of H 2 O 2 . Since GSH counteracts the oxidative stress and Gln participates in TCA cycling, their deficiency may affect the redox balance as well as energy production of sperm cells. These findings shed new light on the pathological mechanisms of infertility associated with LAA. Male infertility patients could benefit from GSH supplement by improvement of acrosin activity and other sperm functions., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The WD40-repeat containing (WDR) proteins are enriched in the testis and play important roles in spermatogenesis. In the present study, we investigate the expression profile of WDR38, a novel member of the WDR protein family, in humans and mice. RT-qPCR (reverse transcription-quantitative polymerase chain reaction) results demonstrate that WDR38 mRNA is abundantly expressed in both the human and mouse testis. The expression of mouse Wdr38 is strictly regulated during development. Further immunofluorescence staining results show that WDR38 is located in the equatorial segment of the acrosome in human and mouse mature spermatozoa and is involved in acrosome biogenesis. Subcellular localization analysis reveals that the mouse Wdr38 protein is distributed in the perinuclear cytoplasm of transfected cells and colocalizes with the GTPase protein Rab19 and Golgi protein GM130. Coimmunoprecipitation (co-IP) assays demonstrate that Wdr38, Rab19 and GM130 interact with each other in the mouse testis and in HEK293T cells. In acrosome biogenesis, Wdr38, Rab19 and GM130 aggregate at the nuclear membrane to form large vesicles, and GM130 then detaches and moves towards the caudal region of the nucleus, whereas the Wdr38/Rab19 complex spreads along the dorsal nuclear edge and finally docks to the equatorial segment. These results indicate that WDR38 is a novel equatorial segment protein that interacts with the GTPase protein RAB19 and Golgi protein GM130 to play roles in acrosome biogenesis.

The zona pellucida (ZP) is an extracellular matrix that surrounds all vertebrate eggs, and it is involved in fertilization and species-specific recognition. Numerous in-depth studies of the ZP proteins of mammals, birds, amphibians, and fishes have been conducted, but systematic investigation of the ZP family genes and their role during fertilization in reptiles has not been reported to date. In this study, we identified six turtle ZP (Tu-ZP) gene subfamilies (Tu-ZP1, Tu-ZP2, Tu-ZP3, Tu-ZP4, Tu-ZPD, and Tu-ZPAX) based on whole genome sequence data from Mauremys reevesii. We found that Tu-ZP4 had large segmental duplication and was distributed on three chromosomes, and we also detected gene duplication in the other Tu-ZP genes. To evaluate the role of Tu-ZP proteins in sperm-egg binding, we assessed the expression pattern of these Tu-ZP proteins and their ability to induce the spermatozoa acrosome reaction in M. reevesii. In conclusion, this is the first report of the existence of gene duplication of Tu-ZP genes and that Tu-ZP2, Tu-ZP3, and Tu-ZPD can induce acrosome exocytosis of spermatogenesis in the reptile., (© The Author(s) 2023. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Each year, infertility affects 15% of couples worldwide, with 50% of cases attributed to men. Globozoospermia is an uncommon cause of male factor infertility, characterized by defects in sperm acrosome formation, leading to round-headed spermatozoa., Objective: We generated Pdcl2 knockout mice to investigate the essential roles of PDCL2 in mammalian reproduction., Materials and Methods: We used reverse transcription-polymerase chain reaction to demonstrate that PDCL2 was expressed exclusively in the male reproductive tract in mice and humans. We created Pdcl2 knockout mice using the CRISPR-Cas9 system and analyzed their fertility. Pdcl2 null spermatozoa underwent further evaluation using computer-assisted sperm analysis, light microscopy, and ultrastructural microscopy. We used immunoblot analysis and immunofluorescence to elucidate relationships between PDCL2 and other acrosomal proteins., Results: The PDC family is highly conserved in eukaryotes. Mouse and human PDCL2 are testis enriched and localized to the testicular endoplasmic reticulum. Loss of the protein causes sterility because of abnormal acrosome biogenesis during spermiogenesis and immotility. Furthermore, Pdcl2 null spermatozoa have rounded heads, similar to globozoospermia in humans. Observation of the knockout testis shows a lack of acrosomal cap formation, aberrant localization of mitochondria in the sperm head, and misshapen nuclei., Conclusion: PDCL2 is essential for sperm acrosome development and male fertility in mice and is a putative contraceptive target in men., (© 2022 American Society of Andrology and European Academy of Andrology.)

The acrosome is a lysosome-related vesicular organelle located in the sperm head. The acrosomal reaction (AR) is an exocytic process mediated by Ca 2+ and essential for mammalian fertilization. Recent findings support the importance of acrosomal alkalinization for the AR. Mibefradil (Mib) and NNC 55-0396 (NNC) are two amphipathic weak bases that block the sperm-specific Ca 2+ channel (CatSper) and induce acrosomal pH (pH a ) increase by accumulating in the acrosomal lumen of mammalian sperm. This accumulation and pH a elevation increase the intracellular Ca 2+ concentration ([Ca 2+ ] i ) and trigger the AR by unknown mechanisms of Ca 2+ transport. Here, we investigated the pathways associated with the pH a increase-induced Ca 2+ signals using mouse sperm as a model. To address these questions, we used single-cell Ca 2+ imaging, the lysosomotropic agent Gly-Phe-β-naphthylamide (GPN) and pharmacological tools. Our findings show that Mib and NNC increase pH a and release acrosomal Ca 2+ without compromising acrosomal membrane integrity. Our GPN results indicate that the osmotic component does not significantly contribute to acrosomal Ca 2+ release caused by pH a rise. Inhibition of two-pore channel 1 (TPC1) channels reduced the [Ca 2+ ] i increase stimulated by acrosomal alkalinization. In addition, blockage of Ca 2+ release-activated Ca 2+ (CRAC) channels diminished Ca 2+ uptake triggered by pH a alkalinization. Finally, our findings contribute to understanding how pH a controls acrosomal Ca 2+ efflux and extracellular Ca 2+ entry during AR in mouse sperm. KEY POINTS: The acrosomal vesicle is a lysosome-related organelle located in the sperm head. The acrosome reaction (AR) is a highly regulated exocytic process mediated by Ca 2+ , which is essential for fertilization. However, the molecular identity of Ca 2+ transporters involved in the AR and their mechanisms to regulate Ca 2+ fluxes are not fully understood. In mammalian sperm, acrosomal alkalinization induces intracellular Ca 2+ concentration ([Ca 2+ ] i ) increase and triggers the AR by unknown molecular mechanisms of Ca 2+ transport. In this study, we explored the molecular mechanisms underlying Ca 2+ signals caused by acrosomal alkalinization using mouse sperm as a model. TPC1 and CRAC channels contribute to [Ca 2+ ] i elevation during acrosomal alkalinization. Our findings expand our understanding of how the acrosomal pH participates in the physiological induction of the AR., (© 2023 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

The acrosome located within the mammalian sperm head is essential for successful fertilization, as it enables the sperm to penetrate the extracellular layers of the oocyte and fuse with oolemma. However, the mammalian acrosomal vesicle is no longer considered to contain only hydrolytic enzymes. Using label-free nano-scale liquid chromatography tandem mass spectrometry (nLC-MS/MS) proteomics, we identified a total of 885 proteins in the acrosome isolated from spermatozoa obtained from cauda epididymis of free-living house mice Mus musculus musculus contains a total of 885 proteins. Among these, 334 proteins were significantly enriched in the acrosome thus representing 27.3% of the whole proteome of the intact sperm. Importantly, we have detected a total of nine calycins while eight of them belong to the lipocalin protein family. In mice, lipocalins are involved in multi-level chemical communication between individuals including pheromone transport and odor perception. Using an indirect immunofluorescence assay, we demonstrated that lipocalin 5 (LCN5) is expressed in the mouse germ cells, and after completing spermatogenesis, it remains localized in the sperm acrosome until the last step of the extratesticular maturation, the acrosome reaction. The presence of lipocalins in the acrosome and acrosome-reacted sperm suggests their original role as chelators of organic and potentially toxic compounds resulting from ongoing spermiogenesis. Along with this evidence, detected mitochondrial (e.g., a subunit of the cytochrome c oxidase MTCO1) and proteasomal proteins (subunits of both 20 S core proteasome [PSMA2, PSMBs] and 19 S regulatory particle [PSMDs]) in acrosomes provide further evidence that acrosomes could also function as `waste baskets` after testicular sperm maturation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier GmbH.. All rights reserved.)

Multiparametric analysis by flow cytometry solves one of the major problems in sperm evaluation, the inability to test multiple attributes simultaneously in a single cell, which would increase the precision to predict fertility potential since several sperm parameters are tested. The association of fluorochromes and compounds conjugated to fluorochromes in multiparametric sperm analysis is well-established in microscopy techniques. However, these techniques are subjective and limit the assessment in small cell numbers, thereby harming analytic accuracy. Therefore, the current study aimed to present new possibilities for assessing the integrity and stability of the sperm plasma membrane, acrosome status, mitochondrial potential, and superoxide anion production in the mitochondrial matrix in only 2 cytometric assays using cytometers equipped with 2 and 3 lasers. For this, human semen samples collected by masturbation and selected by the swim-up technique were divided into 3 treatments: T0 (flash-frozen semen), T50 (flash-frozen semen + fresh semen, V: V), and T100 (fresh semen) for the validation of the multiparametric protocols by flow cytometry. For both protocols, sperm percentage with positive stain for all fluorophores differed significantly between treatments. The determination coefficients presented values close to 1, which validated objective, sensitive, rapid, and reproducible methodologies. Therefore, we concluded that the results reflect the status of analyzed structure, enabling a more accurate diagnosis of male infertility that has become an increasingly prevalent worldwide setback due to exposure to a variety of environmental toxicants., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to disclose., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The acrosome is a membranous organelle positioned in the anterior portion of the sperm head and is essential for male fertility. Acrosome biogenesis requires the dynamic cytoskeletal shuttling of vesicles toward nascent acrosome which is regulated by a series of accessory proteins. However, much remains unknown about the molecular basis underlying this process. Here, we generated Ssh2 knockout (KO) mice and HA-tagged Ssh2 knock-in (KI) mice to define the functions of Slingshot phosphatase 2 (SSH2) in spermatogenesis and demonstrated that as a regulator of actin remodeling, SSH2 is essential for acrosome biogenesis and male fertility. In Ssh2 KO males, spermatogenesis was arrested at the early spermatid stage with increased apoptotic index and the impaired acrosome biogenesis was characterized by defective transport/fusion of proacrosomal vesicles. Moreover, disorganized F-actin structures accompanied by excessive phosphorylation of COFILIN were observed in the testes of Ssh2 KO mice. Collectively, our data reveal a modulatory role for SSH2 in acrosome biogenesis through COFILIN-mediated actin remodeling and the indispensability of this phosphatase in male fertility in mice., Competing Interests: KX, XS, KF, YL, TH, ML, ZW, YY, TM, SL, XC, JJ, JL, WC, JM, GL, ZC, HL No competing interests declared, (© 2023, Xu, Su, Fang et al.)

The development and function of male gametes is dependent on a dynamic microtubule network, yet how this is regulated remains poorly understood. We have recently shown that microtubule severing, via the action of the meiotic AAA ATPase protein clade, plays a crucial role in this process. Here, we sought to elucidate the roles of spastin, an as-yet-unexplored member of this clade in spermatogenesis. Using a SpastKO/KO mouse model, we reveal that spastin loss resulted in a complete loss of functional germ cells. Spastin plays a crucial role in the assembly and function of the male meiotic spindle. Consistent with meiotic failure, round spermatid nuclei were enlarged, indicating aneuploidy, but were still able to enter spermiogenesis. During spermiogenesis, we observed extreme abnormalities in manchette structure, acrosome biogenesis and, commonly, a catastrophic loss of nuclear integrity. This work defines an essential role for spastin in regulating microtubule dynamics during spermatogenesis, and is of potential relevance to individuals carrying spastin variants and to the medically assisted reproductive technology industry., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Na + /H + exchangers (NHEs) are a family of ion transporters that regulate the pH of various cell compartments across an array of cell types. In eukaryotes, NHEs are encoded by the SLC9 gene family comprising 13 genes. SLC9C2, which encodes the NHE11 protein, is the only one of the SLC9 genes that is essentially uncharacterized. Here, we show that SLC9C2 exhibits testis/sperm-restricted expression in rats and humans, akin to its paralog SLC9C1 (NHE10). Similar to NHE10, NHE11 is predicted to contain an NHE domain, a voltage sensing domain, and finally an intracellular cyclic nucleotide binding domain. An immunofluorescence analysis of testis sections reveals that NHE11 localizes with developing acrosomal granules in spermiogenic cells in both rat and human testes. Most interestingly, NHE11 localizes to the sperm head, likely the plasma membrane overlaying the acrosome, in mature sperm from rats and humans. Therefore, NHE11 is the only known NHE to localize to the acrosomal region of the head in mature sperm cells. The physiological role of NHE11 has yet to be demonstrated but its predicted functional domains and unique localization suggests that it could modulate intracellular pH of the sperm head in response to changes in membrane potential and cyclic nucleotide concentrations that are a result of sperm capacitation events. If NHE11 is shown to be important for male fertility, it will be an attractive target for male contraceptive drugs due to its exclusive testis/sperm-specific expression.

The mammalian acrosome is a secretory vesicle attached to the sperm nucleus whose fusion with the overlying plasma membrane is required to achieve fertilization. Acrosome biogenesis starts during meiosis, but it lasts through the entire process of haploid cell differentiation (spermiogenesis). Acrosome biogenesis is a stepwise process that involves membrane traffic from the Golgi apparatus, but it also seems that the lysosome/endosome system participates in this process. Defective sperm head morphology is accompanied by defective acrosome shape and function, and patients with these characteristics are infertile or subfertile. The most extreme case of acrosome biogenesis failure is globozoospermia syndrome, which is primarily characterized by the presence of round-headed spermatozoa without acrosomes with cytoskeleton defects around the nucleus and infertility. Several genes participating in acrosome biogenesis have been uncovered using genetic deletions in mice, but only a few of them have been found to be deleted or modified in patients with globozoospermia. Understanding acrosome biogenesis is crucial to uncovering the molecular basis of male infertility and developing new diagnostic tools and assisted reproductive technologies that may help infertile patients through more effective treatment techniques. This article is categorized under: Reproductive System Diseases > Environmental Factors Infectious Diseases > Stem Cells and Development Reproductive System Diseases > Molecular and Cellular Physiology., (© 2022 Wiley Periodicals LLC.)

Sperm acrosomal membrane proteins, such as Izumo sperm-egg fusion 1 (IZUMO1) and sperm acrosome-associated 6 (SPACA6), play essential roles in mammalian gamete binding or fusion. How their biosynthesis is regulated during spermiogenesis has largely remained elusive. Here, we show that 1700029I15Rik knockout male mice are severely subfertile and their spermatozoa do not fuse with eggs. 1700029I15Rik is a type-II transmembrane protein expressed in early round spermatids but not in mature spermatozoa. It interacts with proteins involved in N -linked glycosylation, disulfide isomerization, and endoplasmic reticulum (ER)-Golgi trafficking, suggesting a potential role in nascent protein processing. The ablation of 1700029I15Rik destabilizes non-catalytic subunits of the oligosaccharyltransferase (OST) complex that are pivotal for N -glycosylation. The knockout testes exhibit normal expression of sperm plasma membrane proteins, but decreased abundance of multiple acrosomal membrane proteins involved in fertilization. The knockout sperm show upregulated chaperones related to ER-associated degradation (ERAD) and elevated protein ubiquitination; strikingly, SPACA6 becomes undetectable. Our results support for a specific, 1700029I15Rik-mediated pathway underpinning the biosynthesis of acrosomal membrane proteins during spermiogenesis.

Membrane fusion in sperm cells is crucial for acrosomal exocytosis and must be preserved to ensure fertilizing capacity. Evolutionarily conserved protein machinery regulates acrosomal exocytosis. Molecular chaperones play a vital role in spermatogenesis and post-testicular maturation. Cysteine string protein (CSP) is a member of the Hsp40 co-chaperones, and the participation of molecular chaperones in acrosomal exocytosis is poorly understood. In particular, the role of CSP in acrosomal exocytosis has not been reported so far. Using western blot and indirect immunofluorescence, we show that CSP is present in human sperm, is palmitoylated, and predominantly bound to membranes. Moreover, using functional assays and transmission electron microscopy, we report that blocking the function of CSP avoided the assembly of trans-complexes and inhibited exocytosis. In summary, here, we describe the presence of CSP in human sperm and show that this protein has an essential role in membrane fusion during acrosomal exocytosis mediating the trans-SNARE complex assembly between the outer acrosomal and plasma membranes. In general, understanding CSP's role is critical in identifying new biomarkers and generating new rational-based approaches to treat male infertility., (© The Author(s) 2022. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Gonadotropin-regulated testicular RNA helicase (GRTH)/DDX25 is a member of DEAD-box family of RNA helicase essential for the completion of spermatogenesis and male fertility, as evident from GRTH-knockout (KO) mice. In germ cells of male mice, there are two species of GRTH, a 56 kDa non-phosphorylated form and 61 kDa phosphorylated form (pGRTH). GRTH Knock-In (KI) mice with R242H mutation abolished pGRTH and its absence leads to infertility. To understand the role of the GRTH in germ cell development at different stages during spermatogenesis, we performed single-cell RNA-seq analysis of testicular cells from adult WT, KO and KI mice and studied the dynamic changes in gene expression. Pseudotime analysis revealed a continuous developmental trajectory of germ cells from spermatogonia to elongated spermatids in WT mice, while in both KO and KI mice the trajectory was halted at round spermatid stage indicating incomplete spermatogenesis process. The transcriptional profiles of KO and KI mice were significantly altered during round spermatid development. Genes involved in spermatid differentiation, translation process and acrosome vesicle formation were significantly downregulated in the round spermatids of KO and KI mice. Ultrastructure of round spermatids of KO and KI mice revealed several abnormalities in acrosome formation that includes failure of pro-acrosome vesicles to fuse to form a single acrosome vesicle, and fragmentation of acrosome structure. Our findings highlight the crucial role of pGRTH in differentiation of round spermatids into elongated spermatids, acrosome biogenesis and its structural integrity.

Aims: This study aimed to explore the effect of epididymosomes on the proliferative efficiency of spermatogonial stem cells (SSCs) in vitro and the resumption of spermatogenesis in the azoospermic mice., Main Methods: The epididymosomes were extracted from the epididymis and characterized. SSCs were cultured in 2D (two-dimensional) and hydrogel-based 3D culture in the presence of 20 μg/mL epididymosome or 10 ng/mL GDNF. After two weeks of culture, the proliferation and purity of the separated SSCs were evaluated using the MTT test and flow cytometry, respectively. qRT-PCR was used to analyze PLZF, caspase-3, TGF-β, miR-10b, and miR-21 expression levels. Then, SSCs grown in the 3D culture system were labeled by DiI and transplanted into azoospermic mice via the efferent duct. After 2 weeks, tracing of DiI and cell homing were evaluated. Subsequently, histomorphometric studies and immunohistochemistry analysis were performed in testes after eight weeks of transplantation., Key Findings: The expression of PLZF, TGF-β, miR-10b, and miR-21 increased significantly (*p < 0.05) in the 3D + GDNF and 3D + epididymosomes groups than in the 2D group. Transplanted SSCs migrated into the seminiferous tubules of recipient mice and the number of spermatogenic cells and protein expression of PLZF, SCP3 and ACRBP in the 3D + GDNF and 3D + epididymosomes groups were considerably higher (∗ ∗ ∗ p < 0.001) compared to the azoospermic group., Significance: This finding indicates that culturing SSCs on decellularized testicular matrix (DTM) hydrogel with 10 ng/mL GDNF or 20 μg/mL epididymosomes could lead to an increase in SSCs proliferation which provides a sufficient number of SSCs for successful transplantation in azoospermic mice., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2022. Published by Elsevier Inc.)

In order to fertilize the egg, spermatozoa must undergo a series of biochemical processes in the female reproductive tract collectively called capacitation. Only capacitated sperm can interact with the egg resulting in the acrosome reaction (AR), allowing egg penetration and fertilization. Sperm can undergo spontaneous AR (sAR) before reaching the egg, preventing successful fertilization. Here we investigated the metabolic pathways involved in sperm capacitation and sAR. Inhibition of glycolysis or oxidative phosphorylation did not affect capacitation or sAR levels; however, when both systems were inhibited, no capacitation occurred, and there was a significant increase in sAR. Under such ATP-starvation, the increase in sAR is triggered by Ca 2+ influx into the sperm via the CatSper cation channel. Protein kinase A (PKA) is an essential key enzyme in sperm capacitation; there was no change in its activity when a single metabolic system was inhibited, while complete inhibition of was observed when the two systems were inhibited. Protein tyrosine phosphorylation (PTP), also known to occur in sperm capacitation, was partially reduced by inhibition of one metabolic system, and completely blocked when the two metabolic systems were inhibited. We conclude that ATP, PKA and PTP are involved in the mechanisms protecting sperm from sAR., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Serine proteases (PRSS) constitute nearly one-third of all proteases, and many of them have been identified to be testis-specific and play significant roles during sperm development and male reproduction. PRSS54 is one of the testis-specific PRSS in mouse and human but its physiological function remains largely unclear. In the present study, we demonstrate in detail that PRSS54 exists not only in testis but also in mature sperm, exhibiting a change in protein size from 50 kDa in testis to 42 kDa in sperm. Loss of PRSS54 in mice results in male subfertility, acrosome deformation, defective sperm-zona penetration, and phenotypes of male subfertility and acrosome deformation can be rescued by Prss54 transgene. Ultrastructure analyses by transmission electronic microscopy further reveal various morphological abnormalities of Prss54-/- spermatids during spermiogenesis, including unfused vacuoles in acrosome, detachment and eccentrical localization of the acrosomal granules, and asymmetrical elongation of the nucleus. Subcellular localization of PRSS54 display that it appears in the acrosomal granule at the early phase of acrosome biogenesis, then extends along the inner acrosomal membrane, and ultimately presents in the acrosome region of the mature sperm. PRSS54 interacts with acrosomal proteins ZPBP1, ZPBP2, ACRBP, and ZP3R, and loss of PRSS54 affects the distribution of these proteins in testis and sperm, although their protein levels are largely unaffected. Moreover, Prss54-/- sperm are more sensitive to acrosome reaction inducers., (© The Author(s) 2022. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In order to penetrate the egg, spermatozoa must undergo the acrosome reaction in close proximity to the egg. This process can take place only after a series of biochemical changes in the sperm, collectively termed capacitation, occur in the female reproductive tract. Sperm cells can undergo spontaneous-acrosome reaction(sAR) before reaching the vicinity of the egg, preventing successful fertilization. Several mechanisms were shown to protect sperm from undergoing sAR, and all of them are involved in proper capacitation. Here, we describe the involvement of protein acetylation in the mechanism that protects bovine spermatozoa from sAR. Incubation of bovine sperm under non-capacitation conditions revealed a strong increase in sAR that was significantly reduced in the presence of deacetylase inhibitors. Protein kinase A (PKA) is an essential key enzyme in sperm capacitation, and its inhibition results in high sAR. The reduction in sAR by hyperacetylation was independent of PKA activity. We previously demonstrated that calmodulin-kinase II (CaMKII) activity protects sperm from sAR, and here we show that its activity is essential for reduction in sAR by hyperacetylation. We further show that the 'exchange protein directly activated by Camp' (EPAC) mediates both protein lysine acetylation and the reduced rate of sAR caused by hyperacetylation. In conclusion, these results suggest a PKA-independent and EPAC-CaMKII dependent hyperacetylation mechanism that protects sperm from sAR., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Glutathione peroxidase 4 (Gpx4) and arachidonic acid 15 lipoxygenase (Alox15) are counterplayers in oxidative lipid metabolism and both enzymes have been implicated in spermatogenesis. However, the roles of the two proteins in acrosomal exocytosis have not been explored in detail. Here we characterized Gpx4 distribution in mouse sperm and detected the enzyme not only in the midpiece of the resting sperm but also at the anterior region of the head, where the acrosome is localized. During sperm capacitation, Gpx4 translocated to the post-acrosomal compartment. Sperm from Gpx4 +/Sec46Ala mice heterozygously expressing a catalytically silent enzyme displayed an increased expression of phosphotyrosyl proteins, impaired acrosomal exocytosis after in vitro capacitation and were not suitable for in vitro fertilization. Alox15-deficient sperm showed normal acrosome reactions but when crossed into a Gpx4-deficient background spontaneous acrosomal exocytosis was observed during capacitation and these cells were even less suitable for in vitro fertilization. Taken together, our data indicate that heterozygous expression of a catalytically silent Gpx4 variant impairs acrosomal exocytosis and in vitro fertilization. Alox15 deficiency hardly impacted the acrosome reaction but when crossed into the Gpx4-deficient background spontaneous acrosomal exocytosis was induced. The detailed molecular mechanisms for the observed effects may be related to the compromised redox homeostasis.

Profilin 4 (Pfn4) is expressed during spermiogenesis and localizes to the acrosome-acroplaxome-manchette complex. Here, we generated PFN4-deficient mice, with sperm displaying severe impairment in manchette formation. Interestingly, HOOK1 staining suggests that the perinuclear ring is established; however, ARL3 staining is disrupted, suggesting that lack of PFN4 does not interfere with the formation of the perinuclear ring and initial localization of HOOK1, but impedes microtubular organization of the manchette. Furthermore, amorphous head shape and flagellar defects were detected, resulting in reduced sperm motility. Disrupted cis- and trans-Golgi networks and aberrant production of proacrosomal vesicles caused impaired acrosome biogenesis. Proteomic analysis showed that the proteins ARF3, SPECC1L and FKBP1, which are involved in Golgi membrane trafficking and PI3K/AKT pathway, are more abundant in Pfn4-/- testes. Levels of PI3K, AKT and mTOR were elevated, whereas AMPK level was reduced, consistent with inhibition of autophagy. This seems to result in blockage of autophagic flux, which could explain the failure in acrosome formation. In vitro fertilization demonstrated that PFN4-deficient sperm is capable of fertilizing zona-free oocytes, suggesting a potential treatment for PFN4-related human infertility., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

Teratozoospermia is a common factor associated with male infertility. However, teratozoospermia characterized by bubble-shaped acrosomes (BSAs) has not yet been identified in men and the causative genes are unknown. The present study is of a patient with severe teratozoospermia characterized by BSA and carrying a variant (c.1204G>A, p.Gly402Ser) of actin-like 7A (ACTL7A). For further verification, we generated an Actl7a-mutated mouse model (p.Gly407Ser) carrying an equivalent variant to that in the patient. We found that homozygous Actl7a-mutated (Actl7aMut/Mut) male mice were sterile, and all their sperm showed acrosomal abnormalities. We detected by transmission electron microscopy that during acrosomal biogenesis, the acrosome detaches from the nuclear membrane in Actl7aMut/Mut mice. Furthermore, mutant ACTL7A failed to attach to the acroplaxome and was discharged by cytoplasmic droplets, which led to the absence of ACTL7A in epididymal spermatozoa in mice. The mutant sperm failed to activate the oocyte, and sperm-borne oocyte activation factor phospholipase C zeta (PLCζ) discharge accompanied by ACTL7A was observed, leading to total fertilization failure (TFF). Immunoprecipitation followed by liquid chromatography-mass spectrometry showed that several differentially expressed proteins participate in acrosome assembly and actin filament organization. Furthermore, assisted oocyte activation by calcium ionophore exposure successfully overcame TFF in the couple with an ACTL7A pathogenic variant. Our study defined a novel phenotype of an acrosomal abnormality characterized by BSA, revealed the underlying mechanism of a pathogenic variant in ACTL7A and provided a genetic marker and potential therapeutic option for male infertility., (© The Author(s) 2022. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Fertilization is an essential process in terrestrial organisms for creating a new organism with genetic diversity. Before gamete fusion, several steps are required to achieve successful fertilization. Animal spermatozoa are first activated and attracted to the eggs by egg-derived chemoattractants. During the sperm passage of the egg's extracellular matrix or upon the sperm binding to the proteinaceous egg coat, the sperm undergoes an acrosome reaction, an exocytosis of acrosome. In hermaphrodites such as ascidians, the self/nonself recognition process occurs when the sperm binds to the egg coat. The activated or acrosome-reacted spermatozoa penetrate through the proteinaceous egg coat. The extracellular ubiquitin-proteasome system, the astacin-like metalloproteases, and the trypsin-like proteases play key roles in this process in ascidians. In the present review, we summarize our current understanding and perspectives on gamete recognition and egg coat lysins in ascidians and consider the general mechanisms of fertilization in animals and plants.

The perinuclear theca (PT) is a cytoskeletal element encapsulating the sperm nucleus; however, the physiological roles of the PT in sperm are largely uncertain. Here, we reveal that ACTRT1, ACTRT2, ACTL7A and ACTL9 proteins interact to form a multimeric complex and localize to the subacrosomal region of spermatids. Furthermore, we engineered Actrt1-knockout (KO) mice to define the functions of ACTRT1. Despite normal sperm count and motility, Actrt1-KO males were severely subfertile owing to a deficiency in fertilization. Loss of ACTRT1 caused a high incidence of malformed heads and detachment of acrosomes from sperm nuclei, caused by loosened acroplaxome structure during spermiogenesis. Furthermore, Actrt1-KO sperm showed reduced ACTL7A and PLCζ protein content as a potential cause of fertilization defects. Moreover, we reveal that ACTRT1 anchors developing acrosomes to the nucleus, likely by interacting with the inner acrosomal membrane protein SPACA1 and the nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 weakened the interaction between ACTL7A and SPACA1. Our study and recent findings of ACTL7A/ACTL9-deficient sperm together reveal that the sperm PT-specific ARP complex mediates the acrosome-nucleus connection., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2022. Published by The Company of Biologists Ltd.)

As a new widespread contaminant, nanoplastics (NPs) pose a potential risk to human health. Nevertheless, the adverse effects of NPs on the male reproductive system are poorly understood. In this study, we aimed to determine the effects of polystyrene nanoplastics (PS-NPs) (50 nm) on sperm quality, with a focus on the acrosome defects. After 35 days of intragastric administration, sperm quality was decreased and testicular structures were impaired in mice exposed to PS-NPs in both the medium (1.0 mg/kg) and high dose (10 mg/kg) groups. No significant changes were observed in the low dose (0.2 mg/kg) group. Meanwhile, acrosome parameters including acrosome integrity and acrosome reaction were decreased after the administration of PS-NPs. These findings were consistent with the disruption of acrosome biogenesis, as identified by the changed testicular ultrastructure. Additionally, the findings were further validated using seven marker genes (Gba2, Pick1, Gopc, Hrb, Zpbp1, Spaca1 and Dpy19l2) essential for acrosome formation, which showed that two of these genes (Gopc and Dpy19l2) were significantly down-regulated. Moreover, repressed autophagy was observed in the testes of PS-NPs-exposed mice based on autophagy-related protein expression. This phenomenon was further verified in GC-2spd cells treated with PS-NPs (50 μg/mL, 100 μg/mL, 200 μg/mL for 24 h). The potential role of autophagy in such acrosome defects was explored by using the autophagy inhibitor 3-methyladenine (3-MA), autophagy activator rapamycin or beclin-1 siRNA. The results showed that Golgi-associated vesicle disorganization was exacerbated with the 3-MA and beclin-1 siRNA pretreatments, but decreased with the rapamycin pretreatment, and the expression of GOPC and DPY19L2 was also altered. These results indicated that autophagy might be involved in the PS-NPs-induced acrosome lesions based on the regulation of two key acrosome-formation proteins, GOPC and DPY19L2. Altogether, our results will provide new insights into the PS-NPs-induced male reproductive impairment., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Secretion of the acrosome, a single vesicle located rostrally in the head of a mammalian sperm, through a process known as "acrosome exocytosis" (AE), is essential for fertilization. However, the mechanisms leading to and regulating this complex process are controversial. In particular, poor understanding of Ca2+ dynamics between sperm subcellular compartments and regulation of membrane fusion mechanisms have led to competing models of AE. Here, we developed a transgenic mouse expressing an Acrosome-targeted Sensor for Exocytosis (AcroSensE) to investigate the spatial and temporal Ca2+ dynamics in AE in live sperm. AcroSensE combines a genetically encoded Ca2+ indicator (GCaMP) fused with an mCherry indicator to spatiotemporally resolve acrosomal Ca2+ rise (ACR) and membrane fusion events, enabling real-time study of AE. We found that ACR is dependent on extracellular Ca2+ and that ACR precedes AE. In addition, we show that there are intermediate steps in ACR and that AE correlates better with the ACR rate rather than absolute Ca2+ amount. Finally, we demonstrate that ACR and membrane fusion progression kinetics and spatial patterns differ with different stimuli and that sites of initiation of ACR and sites of membrane fusion do not always correspond. These findings support a model involving functionally redundant pathways that enable a highly regulated, multistep AE in heterogeneous sperm populations, unlike the previously proposed "acrosome reaction" model., Competing Interests: Conflict of interest A. J. T. discloses that he is a founder and an officer of Androvia LifeSciences, LLC, a biotechnology company investigating solutions for male infertility, in which he holds a minor equity stake. There are no conflicts with the current work. All other coauthors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Globozoospermia is a type of teratozoospermia characterized by round morphology of the sperm head. Gopc -/- infertile globozoospermic murine model has failures during spermiogenesis, such as the incorrect biogenesis of the acrosome, disorganized acroplaxome and manchette, round nuclei and spiral flagella. In this study, Western blot, RT-PCR, immunohistochemistry and immunogold were done for the localization of the acrosome protein Zona Pellucida sperm-binding protein 3 receptor (ZP3R), also called sp56, in wild type and Gopc -/- mice testis. The ZP3R protein was located in the acrosome and pseudo-acrosome vesicles of wild type and Gopc -/- mice, respectively. Also, it is distributed through the cytoplasm of the haploid spermatids only. The incorrect spermiogenesis of Gopc -/- mice causes a deregulation in the expression of ZP3R in the globozoospermic spermatids. Our results suggest that although the lack of GOPC causes a failure during the transport of the pre-acrosomal vesicles, the acrosome protein ZP3R is localized in the acrosome and is distributed through the cytoplasm only during spermiogenesis. Furthermore, the failure in spermiogenesis does not impair the synthesis of ZP3R and its localization in the pre-acrosomal vesicles., (© 2021 The Authors. Microscopy Research and Technique published by Wiley Periodicals LLC.)

Spermatozoon represents a very special cell type in human body, and glycosylation plays essential roles in its whole life including spermatogenesis, maturation, capacitation, sperm-egg recognition, and fertilization. In this study, by mapping the most comprehensive N-glycoproteome of human spermatozoa using our recently developed site-specific glycoproteomic approaches, we show that spermatozoa contain a number of distinctive glycoproteins, which are mainly involved in spermatogenesis, acrosome reaction and sperm:oocyte membrane binding, and fertilization. Heavy fucosylation is observed on 14 glycoproteins mostly located at extracellular and cell surface regions in spermatozoa but not in other tissues. Sialylation and Lewis epitopes are enriched in the biological process of immune response in spermatozoa, while bisected core structures and LacdiNAc structures are highly expressed in acrosome. These data deepen our knowledge about glycosylation in spermatozoa and lay the foundation for functional study of glycosylation and glycan structures in male infertility., Competing Interests: Conflict of interest The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Mammalian sperm capacitation is a prerequisite for successful fertilization. Capacitation involves biochemical and physiological modifications of sperm as they travel through the female reproductive tract. These modifications prepare the sperm to undergo the acrosome reaction (AR), an acrosome vesicle exocytosis that is necessary for gamete fusion. Capacitation requires an increase in both intracellular calcium ([Ca2+]i) and pH (pHi). Mouse sperm capacitation is accompanied by acrosomal alkalinization and artificial elevation of the acrosome pH (pHa) is sufficient to trigger the AR in mouse and human sperm, but it is unknown if pHa increases naturally during human sperm capacitation. We used single-cell imaging and image-based flow cytometry to evaluate pHa during capacitation and its regulation. We found that pHa progressively increases during capacitation. The V-ATPase, which immunolocalized to the acrosome and equatorial segment, is mainly responsible for the acidity of the acrosome. It is likely that the regulation of V-ATPase is at least in part responsible for the progressive increase in pHa during capacitation. Acrosome alkalinization was dependent on extracellular HCO3- and Ca2+. Inhibition of the HCO3--dependent adenylyl cyclase and protein kinase A induced significant pHa changes. Overall, alkalinization of the acrosome may be a key step in the path toward the AR., (© The Author(s) 2022. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

We aimed to analyze the influence of different cellular concentrations of boar sperm suspensions on the induction of capacitation and acrosome reaction. When spermatozoa were incubated at 100 or 200 mill/ml, significant increases in protein tyrosine phosphorylation in the p32 protein were observed, compared to those at 50 mill/ml. In addition, sperm concentration-dependent increases were observed in plasma membrane lipid disorganization (50 mill/ml vs. 200 mill/ml), induction of the acrosome reaction (50 mill/ml vs. 100 mill/ml and 200 mill/ml), and sperm viability (50 mill/ml vs. 100 mill/ml and 200 mill/ml). Our data indicate that an increase in sperm concentration stimulates the induction of capacitation and acrosome reaction in boars.

Katanin microtubule-severing enzymes are crucial executers of microtubule regulation. Here, we have created an allelic loss-of-function series of the katanin regulatory B-subunit KATNB1 in mice. We reveal that KATNB1 is the master regulator of all katanin enzymatic A-subunits during mammalian spermatogenesis, wherein it is required to maintain katanin A-subunit abundance. Our data shows that complete loss of KATNB1 from germ cells is incompatible with sperm production, and we reveal multiple new spermatogenesis functions for KATNB1, including essential roles in male meiosis, acrosome formation, sperm tail assembly, regulation of both the Sertoli and germ cell cytoskeletons during sperm nuclear remodelling, and maintenance of seminiferous epithelium integrity. Collectively, our findings reveal that katanins are able to differentially regulate almost all key microtubule-based structures during mammalian male germ cell development, through the complexing of one master controller, KATNB1, with a 'toolbox' of neofunctionalised katanin A-subunits., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

We studied the effect of extracellular vesicles of the follicular fluid on morphofunctional characteristics of human spermatozoa using CASA (computer-assisted sperm analysis) analytical system. The vesicles were obtained by sequential centrifugation at different rotational speeds and frozen at -80°C in the Sydney IVF Gamete Buffer medium. The sperm fraction was isolated from the seminal fluid of 21 patients aged 27-36 years by differential centrifugation in a density gradient. The precipitate was suspended in Sydney IVF Gamete Buffer to a concentration of 10 6 /ml and incubated with vesicles (1:2) at 37°C in a CO 2 incubator for 30 min and 1 h. Sperm fraction incubated without vesicles served as the control. After incubation, some sperm samples were centrifuged at 700g for 5 min and fixed in 2.5% glutaraldehyde in 0.1 M buffer for transmission electron microscopy. After 30-min and 1-h incubation, the progressive and total sperm motility improved, the curvilinear and linear velocity of spermatozoa did not change significantly. Incubation with vesicles significantly changed the trajectory of sperm movement, which can attest to an increase in their hyperactivation and, probably, fertilizing capacity. Analysis of the effect of extracellular vesicles of follicular fluid on sperm motility will help to improve the effectiveness of assisted reproductive technology programs with male infertility factor by improving sperm characteristics in patients with asthenozoospermia and increasing the fertilizing ability of the sperm., (© 2021. Springer Science+Business Media, LLC, part of Springer Nature.)

Asthenoteratospermia is a common cause of male infertility. Recent studies have revealed that CFAP65 mutations lead to severe asthenoteratospermia due to acrosome hypoplasia and flagellum malformations. However, the molecular mechanism underlying CFAP65-associated sperm malformation is largely unclear. Here, we initially examined the role of CFAP65 during spermiogenesis using Cfap65 knockout (Cfap65-/-) mice. The results showed that Cfap65-/- male mice exhibited severe asthenoteratospermia characterized by morphologically defective sperm heads and flagella. In Cfap65-/- mouse testes, hyper-constricted sperm heads were apparent in step 9 spermatids accompanied by abnormal manchette development, and acrosome biogenesis was abnormal in the maturation phase. Moreover, subsequent flagellar elongation was also severely affected and characterized by disrupted assembly of the mitochondrial sheath (MS) in Cfap65-/- male mice. Furthermore, the proteomic analysis revealed that the proteostatic system during acrosome formation, manchette organization and MS assembly was disrupted when CFAP65 was lost. Importantly, endogenous immunoprecipitation and immunostaining experiments revealed that CFAP65 may form a cytoplasmic protein network comprising MNS1, RSPH1, TPPP2, ZPBP1 and SPACA1. Overall, these findings provide insights into the complex molecular mechanisms of spermiogenesis by uncovering the essential roles of CFAP65 during sperm head shaping, acrosome biogenesis and MS assembly., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Cell-cell fusion is limited to only a few cell types in the body of most organisms and sperm and eggs are paradigmatic in this process. The specialized cellular mechanism of fertilization includes the timely exposure of gamete-specific interaction proteins by the sperm as it approaches the egg. Bindin in sea urchin sperm is one such gamete interaction protein and it enables species-specific interaction with a homotypic egg. We recently showed that Bindin is essential for fertilization by use of Cas9 targeted gene inactivation in the sea urchin, Hemicentrotus pulcherrimus. Here we show phenotypic details of Bindin-minus sperm. Sperm lacking Bindin do not bind to nor fertilize eggs at even high concentrations, yet they otherwise have wildtype morphology and function. These features include head shape, tail length and beating frequency, an acrosomal vesicle, a nuclear fossa, and they undergo an acrosomal reaction. The only phenotypic differences between wildtype and Bindin-minus sperm identified is that Bindin-minus sperm have a slightly shorter head, likely as a result of an acrosome lacking Bindin. These data, and the observation that Bindin-minus embryos develop normally and metamorphose into normal functioning adults, support the contention that Bindin functions are limited to species-specific sperm-egg interactions. We conclude that the evolutionary divergence of Bindin is not constrained by any other biological roles., (© 2021. The Author(s).)

The acrosome is a cap-shaped, Golgi-derived membranous organelle that is located over the anterior of the sperm nucleus and highly conserved throughout evolution. Although morphological changes during acrosome biogenesis in spermatogenesis have been well described, the molecular mechanism underlying this process is still largely unknown. Family with sequence similarity 71, member F1 and F2 (FAM71F1 and FAM71F2) are testis-enriched proteins that contain a RAB2B-binding domain, a small GTPase involved in vesicle transport and membrane trafficking. Here, by generating mutant mice for each gene, we found that Fam71f1 is essential for male fertility. In Fam71f1-mutant mice, the acrosome was abnormally expanded at the round spermatid stage, likely because of enhanced vesicle trafficking. Mass spectrometry analysis after immunoprecipitation indicated that, in testes, FAM71F1 binds not only RAB2B, but also RAB2A. Further study suggested that FAM71F1 binds to the GTP-bound active form of RAB2A/B, but not the inactive form. These results indicate that a complex of FAM71F1 and active RAB2A/B suppresses excessive vesicle trafficking during acrosome formation., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Mammalian spermatogenesis is a highly coordinated process that requires cooperation between specific proteins to coordinate diverse biological functions. For example, mouse Parkin coregulated gene (PACRG) recruits meiosis-expressed gene 1 (MEIG1) to the manchette during normal spermiogenesis. Here we mutated Y68 of MEIG1 using the CRISPR/cas9 system and examined the biological and physiological consequences in mice. All homozygous mutant males examined were completely infertile, and sperm count was dramatically reduced. The few developed sperm were immotile and displayed multiple abnormalities. Histological staining showed impaired spermiogenesis in these mutant mice. Immunofluorescent staining further revealed that this mutant MEIG1 was still present in the cell body of spermatocytes, but also that more MEIG1 accumulated in the acrosome region of round spermatids. The mutant MEIG1 and a cargo protein of the MEIG1/PACRG complex, sperm-associated antigen 16L (SPAG16L), were no longer found to be present in the manchette; however, localization of the PACRG component was not changed in the mutants. These findings demonstrate that Y68 of MEIG1 is a key amino acid required for PACRG to recruit MEIG1 to the manchette to transport cargo proteins during sperm flagella formation. Given that MEIG1 and PACRG are conserved in humans, small molecules that block MEIG1/PACRG interaction are likely ideal targets for the development of male contraconception drugs., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Zinc ion (Zn2+) homeostasis is very important for sperm capacitation and hyperactivation. Zn2+ is a specific inhibitor of the voltage-dependent proton channel (Hv1). Intracellular alkalisation of human spermatozoa is mainly dependent on opening of Hv1. Anandamide may affect spermatozoa through activation of Hv1. An increase in intracellular pH and progesterone (P4) activate cation channels of spermatozoa (CatSper). This study was designed to elucidate the interaction between ZnCl2, P4 and anandamide on human sperm function and intracellular calcium concentrations ([Ca2+]i). Human normal semen samples (n = 30) were diluted (20 × 106 spermatozoa mL-1) and divided into control and ethanol (0.01%)-, anandamide (1 nM)-, ZnCl2 (1 mM)-, P4 (10µM)-, anandamide+ZnCl2- and P4+ZnCl2-treated groups. Sperm kinematics, viability, acrosome status and [Ca2+]i were assessed. The percentage of viable and motile spermatozoa and sperm velocity was reduced in the ZnCl2-treated groups. Anandamide and P4 attenuated the inhibitory effects of ZnCl2 on sperm kinematics. Loss of the acrosome membrane was observed in all experimental groups. P4 and anandamide are present naturally in secretions of the female reproductive tract and modulate the inhibitory effects of ZnCl2 on sperm kinematics. This attenuation is probably due to a change in [Ca2+]i and prevention of Hv1 inactivation by P4 and anandamide respectively.

Fertilization is the fundamental process that initiates the development of a new individual in all sexually reproducing species. Despite its importance, our understanding of the molecular players that govern mammalian sperm-egg interaction is incomplete, partly because many of the essential factors found in nonmammalian species do not have obvious mammalian homologs. We have recently identified the lymphocyte antigen-6 (Ly6)/urokinase-type plasminogen activator receptor (uPAR) protein Bouncer as an essential fertilization factor in zebrafish [S. Herberg, K. R. Gert, A. Schleiffer, A. Pauli, Science 361, 1029-1033 (2018)]. Here, we show that Bouncer's homolog in mammals, Sperm Acrosome Associated 4 (SPACA4), is also required for efficient fertilization in mice. In contrast to fish, in which Bouncer is expressed specifically in the egg, SPACA4 is expressed exclusively in the sperm. Male knockout mice are severely subfertile, and sperm lacking SPACA4 fail to fertilize wild-type eggs in vitro. Interestingly, removal of the zona pellucida rescues the fertilization defect of Spaca4 -deficient sperm in vitro, indicating that SPACA4 is not required for the interaction of sperm and the oolemma but rather of sperm and the zona pellucida. Our work identifies SPACA4 as an important sperm protein necessary for zona pellucida penetration during mammalian fertilization., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Spermiogenesis is the longest phase of spermatogenesis, with dramatic morphological changes and a final step of spermiation, which involves protein degradation and the removal of excess cytoplasm; therefore, we hypothesized that macroautophagy/autophagy might be involved in the process. To test this hypothesis, we examined the function of ATG5, a core autophagy protein in male germ cell development. Floxed Atg5 and Stra8- iCre mice were crossed to conditionally inactivate Atg5 in male germ cells. In Atg5 flox/flox ; Stra8- iCre mutant mice, testicular expression of the autophagosome marker LC3A/B-II was significantly reduced, and expression of autophagy receptor SQSTM1/p62 was significantly increased, indicating a decrease in testicular autophagy activity. The fertility of mutant mice was dramatically reduced with about 70% being infertile. Sperm counts and motility were also significantly reduced compared to controls. Histological examination of the mutant testes revealed numerous, large residual bodies in the lumen of stages after their normal resorption within the seminiferous epithelium. The cauda epididymal lumen was filled with sloughed germ cells, large cytoplasmic bodies, and spermatozoa with disorganized heads and tails. Examination of cauda epididymal sperm by electron microscopy revealed misshapen sperm heads, a discontinuous accessory structure in the mid-piece and abnormal acrosome formation and loss of sperm individualization. Immunofluorescence staining of epididymal sperm showed abnormal mitochondria and acrosome distribution in the mutant mice. ATG5 was shown to induce autophagy by mediating multiple signals to maintain normal developmental processes. Our study demonstrated ATG5 is essential for male fertility and is involved in various aspects of spermiogenesis. Abbreviations : AKAP4: a-kinase anchoring protein 4; ATG5: autophagy-related 5; ATG7: autophagy-related 7; ATG10: autophagy-related 10; ATG12: autophagy-related 12; cKO: conditional knockout; DDX4: DEAD-box helicase 4; MAP1LC3/LC3/tg8: microtubule-associated protein 1 light chain 3; PBS: phosphate-buffered saline; PIWIL2/MILI: piwi like RNA-mediated gene silencing 2; RT-PCR: reverse transcription-polymerase chain reaction; SQSTM1/p62: sequestosome 1; TBC: tubulobulbar complexes; WT: wild type.