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Background: In recent years, the African spiny mouse Acomys cahirinus has been shown to regenerate a remarkable array of severe internal and external injuries in the absence of a fibrotic response, including the ability to regenerate full-thickness skin excisions, ear punches, severe kidney injuries, and complete transection of the spinal cord. While skeletal muscle is highly regenerative in adult mammals, Acomys displays superior muscle regeneration properties compared with standard laboratory mice following several injuries, including serial cardiotoxin injections of skeletal muscle and volumetric muscle loss (VML) of the panniculus carnosus muscle following full-thickness excision injuries. VML is an extreme muscle injury defined as the irrecoverable ablation of muscle mass, most commonly resulting from combat injuries or surgical debridement. Barriers to the treatment of VML injury include early and prolonged inflammatory responses that promote fibrotic repair and the loss of structural and mechanical cues that promote muscle regeneration. While the regeneration of the panniculus carnosus in Acomys is impressive, its direct relevance to the study of VML in patients is less clear as this muscle has largely been lost in humans, and, while striated, is not a true skeletal muscle. We therefore sought to test the ability of Acomys to regenerate a skeletal muscle more commonly used in VML injury models. Methods: We performed two different VML injuries of the Acomys tibialis anterior muscle and compared the regenerative response to a standard laboratory mouse strain, Mus C57BL6/J. Results: Neither Acomys nor Mus recovered lost muscle mass or myofiber number within three months following VML injury, and Acomys also failed to recover force production better than Mus. In contrast, Acomys continued to express eMHC within the injured area even three months following injury, whereas Mus ceased expressing eMHC less than one-month post-injury, suggesting that Acomys muscle was primed, but failed, to regenerate. Conclusions: While the panniculus carnosus muscle in Acomys regenerates following VML injury in the context of full-thickness skin excision, this regenerative ability does not translate to regenerative repair of a skeletal muscle. [ABSTRACT FROM AUTHOR]

Despite the prevalence of large-group living across the animal kingdom, no studies have examined the neural mechanisms that make group living possible. Spiny mice, Acomys , have evolved to live in large groups and exhibit a preference to affiliate with large over small groups. Here, we determine the neural circuitry that facilitates the drive to affiliate with large groups. We first identify an anterior cingulate cortex (ACC) to lateral septum (LS) circuit that is more responsive to large than small groups of novel same-sex peers. Using chemogenetics, we then demonstrate that this circuit is necessary for both male and female group investigation preferences but only males' preference to affiliate with larger peer groups. Furthermore, inhibition of the ACC-LS circuit specifically impairs social, but not nonsocial, affiliative grouping preferences. These findings reveal a key circuit for the regulation of mammalian peer group affiliation. • Spiny mice, but not C57BL/6J mice, exhibit affiliative-peer-group preferences • The ACC-LS circuit is necessary for group investigation preferences in spiny mice • Inhibition of the ACC-LS reverses affiliative group preferences in male spiny mice • The ACC-LS circuit does not modulate nonsocial group size preferences in spiny mice Fricker et al. demonstrate that the ACC-LS circuit is necessary for peer group size preferences in communally breeding male and female spiny mice. These findings show that the ACC-LS circuit is an integral mediator of peer group affiliation responses that are likely critical for the formation and possibly the cohesion of complex mammalian societies. [ABSTRACT FROM AUTHOR]

Abstract Background In recent years, the African spiny mouse Acomys cahirinus has been shown to regenerate a remarkable array of severe internal and external injuries in the absence of a fibrotic response, including the ability to regenerate full-thickness skin excisions, ear punches, severe kidney injuries, and complete transection of the spinal cord. While skeletal muscle is highly regenerative in adult mammals, Acomys displays superior muscle regeneration properties compared with standard laboratory mice following several injuries, including serial cardiotoxin injections of skeletal muscle and volumetric muscle loss (VML) of the panniculus carnosus muscle following full-thickness excision injuries. VML is an extreme muscle injury defined as the irrecoverable ablation of muscle mass, most commonly resulting from combat injuries or surgical debridement. Barriers to the treatment of VML injury include early and prolonged inflammatory responses that promote fibrotic repair and the loss of structural and mechanical cues that promote muscle regeneration. While the regeneration of the panniculus carnosus in Acomys is impressive, its direct relevance to the study of VML in patients is less clear as this muscle has largely been lost in humans, and, while striated, is not a true skeletal muscle. We therefore sought to test the ability of Acomys to regenerate a skeletal muscle more commonly used in VML injury models. Methods We performed two different VML injuries of the Acomys tibialis anterior muscle and compared the regenerative response to a standard laboratory mouse strain, Mus C57BL6/J. Results Neither Acomys nor Mus recovered lost muscle mass or myofiber number within three months following VML injury, and Acomys also failed to recover force production better than Mus. In contrast, Acomys continued to express eMHC within the injured area even three months following injury, whereas Mus ceased expressing eMHC less than one-month post-injury, suggesting that Acomys muscle was primed, but failed, to regenerate. Conclusions While the panniculus carnosus muscle in Acomys regenerates following VML injury in the context of full-thickness skin excision, this regenerative ability does not translate to regenerative repair of a skeletal muscle.

There is increasing interest in the African spiny mouse (Acomys cahirinus) as a model organism because of its ability for regeneration of tissue after injury in skin, muscle, and internal organs such as the kidneys. A high-quality reference genome is needed to better understand these regenerative properties at the molecular level. Here, we present an improved reference genome for A. cahirinus generated from long Nanopore sequencing reads. We confirm the quality of our annotations using RNA sequencing data from 4 different tissues. Our genome is of higher contiguity and quality than previously reported genomes from this species and will facilitate ongoing efforts to better understand the regenerative properties of this organism. [ABSTRACT FROM AUTHOR]

Current research using animal models to investigate retinal cell biology and model retinal degenerative diseases largely utilize small mammals that are nocturnal and lack the ability to restore lost vision. In contrast, the Mongolian gerbil (Meriones) is a diurnal rodent with good photopic vision, and the spiny mouse (Acomys) is a small desert-dwelling rodent with remarkable regenerative capabilities. The goal of this study was to identify antibodies that detect retinal cell classes in Meriones and Acomys , and to describe the retinal anatomy of these two species in comparison to outbred laboratory mice (Mus musculus). Immunohistochemistry was performed on retinal sections with antibodies for various retinal cell types. Sections were imaged by light, fluorescence, and confocal microscopy. Cell density, morphology, and placement were compared between species qualitatively and quantitatively. Our analyses revealed a classic assembly of retinal cells in Meriones and Acomys , with a few deviations compared to Mus. Meriones displayed the highest density of cones and Acomys the lowest. A higher density of bipolar cell bodies in the proximal portion of the inner nuclear layer was observed in both Acomys and Meriones compared to Mus , and both species exhibited an increase in amacrine cell density compared to Mus. Our results provide a foundation for future research into the visual system adaptations of these interesting species. • Comparisons of cell density between Acomys , Meriones and Mus musculus revealed that Meriones have the highest, and Acomys the lowest, density of cone photoreceptors, among the three species. • Both Meriones and Acomys display an increased density of bipolar cell bodies in the proximal portion of the INL relative to Mus , with Meriones having an overall increase in bipolar cell density. • Amacrine cells are present at higher density in both Meriones and Acomys relative the Mus. • We have identified a panel of commercially available antibodies that permit detection and quantification of retinal cell types in Acomys dimidiatus (the spiny mouse) and Meriones unguiculatus (the Mongolian gerbil). [ABSTRACT FROM AUTHOR]

Abstract Background The Egyptian spiny mouse (Acomys cahirinus) is the only known rodent to exhibit true, human-like menstruation and postpartum ovulation, and is an important new model for reproductive studies. Spiny mice do not produce a visible copulatory plug, and calculation of gestational age is therefore restricted by the need to use mated postpartum dams. The current inefficient method of monitoring until parturition to provide a subsequent estimate of gestational age increases study duration and costs. This study addressed this issue by comparing the mating behaviour of spiny mice across the menstrual cycle and proposes a more accurate method for staging and pairing animals that provides reliable estimates of gestational age. In experiment 1, mating behaviour was recorded overnight to collect data on mounting, intromission, and ejaculation (n = 5 pairs per stage) in spiny mice paired at menses and at early and late follicular and luteal phases of the menstrual cycle. In experiment 2, female spiny mice were paired at the follicular or luteal phases of the menstrual cycle to determine any effect on the pairing-birth interval (n = 10 pairs). Results We report a broad mating window of ~ 3 days during the follicular phase and early luteal phase of spiny mice. Males displayed a discrete ‘foot twitch’ behaviour during intromission and a brief copulatory lock during ejaculation. Litters were delivered after 40–43 days if pairing occurred during the mating window, compared with 46–48 days for spiny mice paired in the late luteal phase. When pairing occurred during the late luteal phase or menses no mating activity was observed during the recording period. Conclusion This study clearly demonstrates an effect of the menstrual cycle on mating behaviour and pregnancy in the spiny mouse and provides a reliable and more effective protocol for estimating gestational age without the need for postpartum dams.

Background: The Egyptian spiny mouse (Acomys cahirinus) is the only known rodent to exhibit true, human-like menstruation and postpartum ovulation, and is an important new model for reproductive studies. Spiny mice do not produce a visible copulatory plug, and calculation of gestational age is therefore restricted by the need to use mated postpartum dams. The current inefficient method of monitoring until parturition to provide a subsequent estimate of gestational age increases study duration and costs. This study addressed this issue by comparing the mating behaviour of spiny mice across the menstrual cycle and proposes a more accurate method for staging and pairing animals that provides reliable estimates of gestational age. In experiment 1, mating behaviour was recorded overnight to collect data on mounting, intromission, and ejaculation (n = 5 pairs per stage) in spiny mice paired at menses and at early and late follicular and luteal phases of the menstrual cycle. In experiment 2, female spiny mice were paired at the follicular or luteal phases of the menstrual cycle to determine any effect on the pairing-birth interval (n = 10 pairs). Results: We report a broad mating window of ~ 3 days during the follicular phase and early luteal phase of spiny mice. Males displayed a discrete 'foot twitch' behaviour during intromission and a brief copulatory lock during ejaculation. Litters were delivered after 40–43 days if pairing occurred during the mating window, compared with 46–48 days for spiny mice paired in the late luteal phase. When pairing occurred during the late luteal phase or menses no mating activity was observed during the recording period. Conclusion: This study clearly demonstrates an effect of the menstrual cycle on mating behaviour and pregnancy in the spiny mouse and provides a reliable and more effective protocol for estimating gestational age without the need for postpartum dams. [ABSTRACT FROM AUTHOR]

The African spiny mouse (Acomys cahirinus) is a unique mammalian model of tissue regeneration, regenerating 4 mm ear-hole punches with cartilage, adipocytes, hair follicles, and muscle. However, the time to regenerate ear tissue varies from 20 to 90 days and muscle regeneration is inconsistent. Some report that older spiny mice have delayed regeneration without investigation on the regenerative capacity of muscle. We thought that delayed regeneration and inconsistent muscle regeneration could be linked via age-related nerve degeneration. While the current study found that spiny mice aged 6-9 months had delayed regeneration compared to 3-4 month-old spiny mice, the capacity of muscle regeneration was unrelated to age, and there was little evidence for age-related nerve degeneration. Instead, the regeneration of muscle, cartilage and adipocytes was spatially heterogeneous, declining in amount from the proximal to distal region of the regenerated tissue. Also, cartilage regeneration in the distal region was decreased in ≥22-month-old Acomys and adipocyte regeneration was decreased in those older than 6 months, compared to 3-4 month olds. While the underlying mechanisms for delayed and spatially heterogenous regeneration remain unclear, age and the spatial region of the regenerated tissue should be considered in experimental designs with spiny mice., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

The vast majority of neural stem cell studies have been conducted on the brains of mice and rats, the classical model rodent. Non‐model organisms may, however, give us some important insights into how to increase neural stem cell numbers for regenerative purposes and with this in mind we have characterized these cells in the brain of the spiny mouse, Acomys cahirinus. This unique mammal is highly regenerative and damaged tissue does not scar or fibrose. We find that there are more than three times as many stem cells in the SVZ and more than 3 times as many proliferating cells compared to the CD‐1 outbred strain of lab mouse. These additional cells create thick stem cell regions in the wall of the SVZ and very obvious columns of cells moving into the rostral migratory stream. In the dentate gyrus, there are more than 10 times as many cells proliferating in the sub‐granular layer and twice the number of doublecortin expressing neuroblasts. A preliminary analysis of some stem cell niche genes has identified Sox2, Notch1, Shh, and Noggin as up‐regulated in the SVZ of Acomys and Bmp2 as being down‐regulated. The highly increased neural stem cell numbers in Acomys may endow this animal with increased regenerative properties in the brain or improved physiological performance important for its survival. [ABSTRACT FROM AUTHOR]

Phylogeographic patterns in the Horn of Africa have recently attracted researchers searching for hidden diversity and explaining the evolutionary history of this region. In this paper, we focus on spiny mouse Acomys louisae. We examined 88 samples from 13 localities across Somaliland and sequenced CYTB, control region and IRBP genes. Phylogenetic analysis confirmed clear distinctness of A. louisae from the other clades of Acomys, but it also revealed deep splits within A. louisae clade. Samples from Central and Eastern Somaliland, including those from the type locality, form a clearly distinct Somaliland clade while remaining ones from the very NW of Somaliland and 5 previously published sequences from Djibouti and E Ethiopia form a Djibouti group. At two localities in the contact zone, we detected sympatric occurrence of both. The clades exhibit sharply contrasting patterns of variability, the Somaliland clade is characterized by a sufficient mitochondrial haplotype diversity, but low sequence divergence. The population parameters and haplotype networks suggest that the populations belonging to the Somaliland clade probably underwent a recent expansion of its range and population size. It may be explained by a repopulation after the interglacial period providing poor environmental conditions for spiny mice in E and C Somaliland. In contrast, the Djibouti group shows extremely high nucleotide diversity besides that of haplotype one. This suggests a long-term persistence of large and/or structured populations. It may be attributed to a specific history of the Ethiopian Rift and Afar. The results emphasize the importance of the Horn of Africa as a region preserving high endemism. [ABSTRACT FROM AUTHOR]

The spiny mouse, Acomys spp., is a recently described model organism for regeneration studies. For a mammal, it displays surprising powers of regeneration because it does not fibrose (i.e. scar) in response to tissue injury as most other mammals, including humans, do. In this Primer article, we review these regenerative abilities, highlighting the phylogenetic position of the spiny mouse relative to other rodents.We also briefly describe the Acomys tissues that have been used for regeneration studies and the common features of their regeneration compared with the typical mammalian response. Finally, we discuss the contribution that Acomys has made in understanding the general principles of regeneration and elaborate hypotheses as to why this mammal is successful at regenerating. [ABSTRACT FROM AUTHOR]

The details of how macrophages control different healing trajectories (regeneration vs. scar formation) remain poorly defined. Spiny mice (Acomys spp.) can regenerate external ear pinnae tissue, whereas lab mice (Mus musculus) form scar tissue in response to an identical injury. Here, we used this dual species system to dissect macrophage phenotypes between healing modes. We identified secreted factors from activated Acomys macrophages that induce a pro-regenerative phenotype in fibroblasts from both species. Transcriptional profiling of Acomys macrophages and subsequent in vitro tests identified VEGFC, PDGFA, and Lactotransferrin (LTF) as potential pro-regenerative modulators. Examining macrophages in vivo , we found that Acomys -resident macrophages secreted VEGFC and LTF, whereas Mus macrophages do not. Lastly, we demonstrate the requirement for VEGFC during regeneration and find that interrupting lymphangiogenesis delays blastema and new tissue formation. Together, our results demonstrate that cell-autonomous mechanisms govern how macrophages react to the same stimuli to differentially produce factors that facilitate regeneration. [Display omitted] • Acomys macrophages exhibit a reduced inflammatory phenotype • Secretory factors from Acomys macrophages induce regenerative fibroblast behavior • Macrophage-secreted VEGFC facilitates complex tissue regeneration in Acomys Macrophage secretory factors play distinct roles during tissue repair. Comparing tissue healing in spiny mice (regenerative) and laboratory mice (non-regenerative), Simkin and Aloysius et al. show that specific substances released by resident macrophages (e.g., VEGFC and LTF) facilitate complex tissue regeneration in spiny mice. [ABSTRACT FROM AUTHOR]

While spiny mice are primarily used as a model for Type II diabetes and for studying complex tissue regeneration, they are also an emerging model for a variety of studies examining hormones, behavior, and the brain. We began studying the spiny mouse to take advantage of their highly gregarious phenotype to examine how the brain facilitates large group-living. However, this unique rodent can be readily bred and maintained in the lab and can be used to ask a wide variety of scientific questions. In this brief communication we provide an overview of studies that have used spiny mice for exploring physiology and behavior. Additionally, we describe how the spiny mouse can serve as a useful model for researchers interested in studying precocial development, menstruation, cooperation, and various grouping behaviors. With increasingly available technological advancements for non-traditional organisms, spiny mice are well-positioned to become a valuable organism in the behavioral neuroscience community. • Spiny mice are a large group-living rodent amenable for lab studies. • Spiny mice have a unique physiology and are precocial and exhibit menstruation. • Spiny mice are highly prosocial in both reproductive and nonreproductive contexts. • Spiny mice are excellent for studying grouping and cooperative behavior. [ABSTRACT FROM AUTHOR]

Wound‐induced hair follicle neogenesis (WIHN) has been demonstrated in laboratory mice (Mus musculus) after large (>1.5 × 1.5 cm2) full‐thickness wounds. WIHN occurs more robustly in African spiny mice (Acomys cahirinus), which undergo autotomy to escape predation. Yet, the non‐WIHN regenerative ability of the spiny mouse skin has not been explored. To understand the regenerative ability of the spiny mouse, we characterized skin features such as hair types, hair cycling, and the response to small and large wounds. We found that spiny mouse skin contains a large portion of adipose tissue. The spiny mouse hair bulge is larger and shows high expression of stem cell markers, K15 and CD34. All hair types cycle synchronously. To our surprise, the hair cycle is longer and less frequent than in laboratory mice. Newborn hair follicles in anagen are more mature than C57Bl/6 and demonstrate molecular features similar to C57Bl/6 adult hairs. The second hair cycling wave begins at week 4 and lasts for 5 weeks, then telogen lasts for 30 weeks. The third wave has a 6‐week anagen, and even longer telogen. After plucking, spiny mouse hairs regenerate in about 5 days, similar to that of C57Bl/6. After large full‐thickness excisional wounding, there is more de novo hair formation than C57Bl/6. Also, all hair types are present and pigmented, in contrast to the unpigmented zigzag hairs in C57Bl/6 WIHN. These findings shed new light on the regenerative biology of WIHN and may help us understand the control of skin repair vs regeneration. [ABSTRACT FROM AUTHOR]

Members of the Acomys genus, known as spiny mice, are unique among mammals in being perfectly capable of regenerating large areas of skin that have been removed. During this regenerative process hairs, sebaceous glands, erector pili muscles, adipocytes and the panniculus carnosus all regenerate and the dermis does not scar. We review here the processes that the epidermis and the individual components of the dermis undergo during spiny mouse regeneration as well as the molecules that have been identified as potentially important in regeneration. We then relate this to what has been proposed as playing a role in studies from the laboratory mouse, Mus musculus. Differences in the immune systems of spiny mice and laboratory mice are also highlighted as this is suggested to play a part not only in the perfect wound healing that embryos display but also in regeneration in lower vertebrates. [ABSTRACT FROM AUTHOR]

Study Question: Does the newly discovered menstruating spiny mouse exhibit behavioural and metabolic changes in correlation with premenstrual phases of the menstrual cycle?Summary Answer: This is the first report of cycle variability in the exploratory and interactive behaviour, and food consumption in menstruating spiny mice, and demonstrates that physiological changes are also dependent on within-subject variation.What Is Known Already: Premenstrual syndrome (PMS) is a prominent cyclic disorder that affects millions of women worldwide. More than 70% of women endure symptoms of impending menstruation, such as bloating, abdominal cramping and nausea to some degree. Consequently, ~8% of women experience recurrent physical and emotional symptoms which are extreme enough to disrupt daily life and seek intervention. Due to a lack of an appropriate animal model, the mechanisms underlying PMS are poorly understood, and subsequently, effective treatments are limited.Study Design, Size, Duration: This study analyses the changes in behavioural responses to the investigator during vaginal lavage (n = 14), exploratory behaviour (n = 11) and metabolism (n = 20) across the menstrual cycle in the spiny mouse (Acomys cahirinus).Participants/materials, Setting, Methods: We performed vaginal lavages on virgin spiny mice (6-8 months of age) and subjected each cohort of females to repeated measures for vaginal lavage, exploratory behaviour and metabolism. Stages of the menstrual cycle were designated as early follicular, late follicular, early luteal, late luteal, early menstrual and late menstrual, with the late luteal and early menstrual phases considered as premenstrual phases and analysed using generalized estimating equations. For vaginal lavage, the behavioural responses to researcher handling were scored on an increasing scale of severity during the lavage process (e.g. restraint, frequency of vocalizations, total handling time). For exploratory behaviour, exploration, memory and sociability were assessed through subjection to Open Field (OF), Novel Object Recognition (NORT), Social Novelty (SN) and Elevated Plus Maze (EPM) tests. For metabolism, physiological changes were measured over a 24-h period in metabolic cages. Results are mean ± SD with statistical significance set to P < 0.05.Main Results and the Role Of Chance: Qualitative behavioural assessment showed that compared to early follicular controls, during premenstrual phases, cycling females had significantly increased probability of: manifesting difficulties during restraint (4×, P < 0.01), vocalizing (8×, P < 0.01) and exhibiting isolation in the cage (40×, P = 0.041). We saw significant increases in handling time during the premenstrual phase in cycling females (76 ± 16 s) compared to controls (55 ± 7 s, P < 0.001). For exploratory behaviour, cycling females in their early menstrual phase travelled significantly less distance in the outer zone of the OF arena (13.3 ± 9.0 m) than females in their early luteal phase (22.3 ± 9.9 m, P = 0.038) and at significantly reduced velocities (40.2 ± 10.5 mm/s and 78.8 ± 31.0 mm/s, respectively, P = 0.006). These females also had fewer entries into the EPM open arms during the same phases (9.6 ± 6.1 and versus 20.0 ± 7.2, respectively, P = 0.030) and travelled less distance (3.2 ± 2.8 m versus 7.0 ± 5.5 m, respectively, P = 0.026). No differences were observed in NORT or SN across the cycle. In the metabolism studies, spiny mice demonstrated a significant increase in food consumption (percentage of body weight) during the early follicular and late luteal phases (3.9 ± 2.4% and 3.8 ± 2.1%, respectively) compared to the late follicular phase (2.3 ± 2.6%, P = 0.015).Large Scale Data: N/A.Limitations, Reasons For Caution: This is an observational study to determine fundamental changes in behaviour and metabolism in a novel species, and as such, lacks commercially available laboratory reagents and protocols specific to the spiny mouse.Wider Implications Of the Findings: The timing of these behavioural and physiological changes suggests that spiny mice exhibit symptoms analogous to PMS in higher order primates, thus providing a pre-clinical model for testing novel interventions to alleviate premenstrual symptoms and overcoming many limitations associated with this research area.Study Funding/competing Interest(s): N.B. is supported by a Research Training Program stipend through Monash University. J.E. is supported by a Fellowship awarded by the Peter Fielding Foundation. The Hudson Institute of Medical Research is supported by the Victorian Government Operational Research Infrastructure Support. The authors declare no conflicts of interest. [ABSTRACT FROM AUTHOR]

The spiny mouse, Acomys cahirinus, shows remarkable regenerative abilities after excisional skin wounding by regrowing hair, sebaceous glands, smooth muscle, skeletal muscle and dermis without scarring. We have asked here whether this same regeneration can be seen after full thickness thermal burn injuries. Using a brass rod thermal injury model we show that in contrast to the lab mouse, Mus musculus, which forms a thick scar covered by a hairless epidermis, the spiny mouse regenerates all the tissues injured - skeletal muscle, dermis, hairs, sebaceous glands such that the skin is externally indistinguishable from its original appearance. Re-epithelialization is faster in Acomys than in Mus but ingression and proliferation of dermal fibroblasts is the same in both species. After 3 weeks the wound epithelium of Acomys has developed a covering of new hair follicles in contrast to Mus. The skeletal muscle of the panniculus carnosus in Mus shows some regeneration but it is incomplete and fibrotic whereas the Acomys muscle is replaced perfectly. There are differences in the macrophage profiles which invade the damaged tissues such as the absence of F4/80 or MOMA-2 +ve cells in Acomys which likely reflect different cytokine profiles resulting from the same injury in these two species. [ABSTRACT FROM AUTHOR]

Study Question: Is the newly discovered menstruating rodent, the spiny mouse, a valid model for studying endometrial morphology and menstruation?Summary Answer: Our study is the first to demonstrate a primate-like pattern of natural menstruation in a rodent, with decidualization, spiral arteriole remodeling and piece-meal endometrial shedding.What Is Known Already: The spiny mouse has a naturally occurring menstrual cycle. This unique feature has the potential to reduce the heavy reliance on primates and provide a more appropriate small animal model for menstrual physiology research.Study Design, Size, Duration: This study compares morphological changes in the endometrium during early, mid and late menstruation of the spiny mouse (n = 39), human (n = 9) and the induced mouse model of menstruation (n = 17).Participants/materials, Setting, Methods: We assessed tissue morphology with hematoxylin and eosin and erythrocyte patterns with Mallory's trichrome. We conducted staining for neutrophil gelatinase associated lipocalin (NGAL), cytokeratin and interleukin-11 (IL-11) in all species. We used double immunofluorescence staining for vascular endothelial growth factor and alpha-smooth muscle actin to detect vasculature remodeling and western immunoblot to detect interleukin-8 (IL-8) and macrophage migration inhibitory factor (MIF) in the menstrual fluid of spiny mice.Main Results and the Role Of Chance: Menstruation occurs in the spiny mouse over a 72-h period, with heaviest menstrual breakdown occurring 24 h after initial observation of red blood cells in the vaginal cytology. During menstruation, the endometrium of the spiny mouse appeared to resemble human menstrual shedding with focal epithelial breakdown observed in conjunction with lysis of underlying stroma and detection of IL-8 and MIF in menstrual fluid. The mouse exhibits extensive decidualization prior to induced menses, with transformation of the entire uterine horn and cytokeratin expression absent until initiation of repair. Decidualization occurred spontaneously and was less marked in the spiny mouse, where epithelial integrity remained intact. In all species, the decidua was positive for IL-11 secretion and neutrophil recruitment was similar in each. Spiral arteriole formation was confirmed in the spiny mouse.Large Scale Data: N/A.Limitations, Reasons For Caution: This is a descriptive study comparing primarily morphological traits between the spiny mouse, the mouse and the human. Reagents specific to the spiny mouse were limited and resources for global use of this novel species are few.Wider Implications Of the Findings: Our work supports the spiny mouse as a viable model, sharing many attributes of physiological menstruation with humans. The strength of a natural as opposed to an artificial model is validated through the striking similarities observed between the spiny mouse and human in uterine breakdown. The spiny mouse may be highly useful in large-scale investigations of menstruation and menstrual disorders.Study Funding/competing Interest(s): N.B. and S.R. are each recipients of a Research Training Program scholarship supported by Monash University. This work was supported by the Victorian Government Operational Infrastructure and laboratory funds to H.D. The authors declare no competing interests. [ABSTRACT FROM AUTHOR]

This brief review considers the question of why some animals can regenerate and others cannot and elaborates the opposing views that have been expressed in the past on this topic, namely that regeneration is adaptive and has been gained or that it is a fundamental property of all organisms and has been lost. There is little empirical evidence to support either view, but some of the best comes from recent phylogenetic analyses of regenerative ability in Planarians which reveals that this property has been lost and gained several times in this group. In addition, a nonregenerating species has been induced to regenerate by altering only one signaling pathway. Extrapolating this to mammals it may be the case that there is more regenerative ability in mammals than has typically been thought to exist and that inducing regeneration in humans may not be as impossible as it may seem. The regenerative abilities of mammals is described and it turns out that there are several examples of classical epimorphic regeneration involving a blastema as exemplified by the regenerating Urodele limb that can be seen in mammals. Even the heart can regenerate in mammals which has long been considered to be a property unique to Urodeles and fish and several recent examples of regeneration have come from recent studies of the spiny mouse, Acomys, which are discussed here. It is suggested that a much more thorough phylogenetic analysis of mammalian regeneration would likely reveal some important insights into the evolution of regeneration. [ABSTRACT FROM AUTHOR]