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.
- Animal model
- Spiny mouse