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Spermatozoa are highly differentiated cells whose ultimate function is fertilization to successfully transfer the male genome. This achievement relies on the expression, localization, organization, and proper functionality of their molecular components. For years, proteomics emerged as a remarkable approach for fertility research to identify specific protein markers related to sperm competency. Such biomarkers, undetected with conventional semen analysis methods, are next-generation tools to assess sperm functionality and predict male fertility. Among them, the proAKAP4 marker is a sperm-specific protein, synthesized as the precursor of AKAP4, highly conserved among mammals and only present in the principal piece of the flagellum. ProAKAP4 entails a disposable stock of AKAP4 to ensure long-lasting sperm motility up to the fecundation site, capacitation, and fertility. By being either converted into mature and active AKAP4 or degraded by proteolysis, proAKAP4 is a stress sensor, acting as a potential gatekeeper to prevent transmission of unfavorable genetic damage to the next generation. Loss or decrease of AKAP4 expression does not affect the number of spermatozoa produced but it impacted sperm motility, viability, and fecundation. A method based on proAKAP4 concentration measurement in a defined number of spermatozoa recently appeared as a simple, reliable, reproducible, robust, and quantitative tool to assess more objectively semen quality and predict male fertility. In this review, we will discuss how fundamental discoveries around the proAKAP4 biomarker provide a yet missing molecular dimension in semen analysis assessments to ensure higher semen quality and reproductive performance in veterinary clinics, zoos, and wild animal reproduction centers., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Functional sperm quality markers to predict bull fertility have been actively investigated. Among them, proAKAP4, which is the precursor of AKAP4, the main structural protein in the fibrous sheath of spermatozoa; appears to be promising, especially since spermatozoa lacking AKAP4 expression were shown to be immotile, abnormal, and infertile. In this study, the objective was to evaluate proAKAP4 concentration values with the classic sperm motility descriptors and fertility outcomes (NRR at 90 days) in post-thawed conditions of 10 bulls' semen. ProAKAP4 expression was confirmed by Western blotting and proAKAP4 concentrations were determined by ELISA. Variations in proAKAP4 concentrations were observed independently of the motility sperm descriptors measured using computer-assisted semen analysis (CASA). A ProAKAP4 concentration of 38.67 ± 8.55 ng/10 million spermatozoa was obtained as a statistical mean of all samples. Threshold values of proAKAP4 were then determined between 19.96 to 96.95 ng/10 million spermatozoa. ProAKAP4 concentrations were positively correlated with progressive motility and the linearity coefficient. The sperm showing the lowest progressive motility were the samples exhibiting proAKAP4 concentrations below 20 ng/10 million spermatozoa. Furthermore, proAKAP4 concentrations were significantly higher in bulls with a higher NRR in the field. Our results demonstrate a correlation between the semen concentration of proAKAP4 and NRR-90d (p = 0.05) in post-thawed bull semen, highlighting the potential of proAKAP4 as a predictive marker of bull fertility. [ABSTRACT FROM AUTHOR]

The current study aimed to explore the potential usefulness of liquid or lyophilized egg yolk plasma (EYP) as a substitute for low‐density lipoproteins (LDL) for cryopreservation of canine spermatozoa. In the first experiment, a total of 20 ejaculates harvested from six Beagles were frozen in extenders containing 6% LDL (control) or liquid or lyophilized EYP at one of three concentrations (20%, 40% or 60%). Motility parameters were assessed 10 min after thawing using computer‐assisted sperm analysis. For both liquid and lyophilized EYP, the 40% concentration yielded motility similar (p > 0.05) to that observed with the control extender. In the second experiment, 12 ejaculates collected from the same six dogs were frozen in 6% LDL (Control), 40% liquid EYP or 40% lyophilized EYP extenders. Spermatozoal membrane integrity (hypo‐osmotic swelling test [HOSt] and SYBR14/propidium iodide [PI] staining), acrosome integrity (FITC‐Pisum sativum agglutinin staining) and DNA integrity (acridine orange staining) characteristics were evaluated 10 min after thawing. Both liquid and lyophilized 40% EYP‐based extenders successfully preserved all assessed integrity parameters as efficiently as the control. Results of this study suggest that lyophilized EYP is a viable alternative to LDL in freezing extenders for dog semen. [ABSTRACT FROM AUTHOR]