Menstruating Mice

Press/Media: Research


Nadia Bellofiore et al. have discovered a rodent species that menstruates [1]. The spiny mouse (Acomys cahirinus) joins 0.09% of menstruating non-primate mammals out of the known 5502 mammals; as such, this discovery is an invaluable windfall to the field of reproductive science. Existing mouse models can be manipulated to exhibit menstruation, but they are of limited use when attempting to understand nuances of menstruation-related disorders, are costly to produce, and difficult to maintain.

Menstruation is defined as the cyclical shedding of the endometrium post-decidualization in the absence of a pregnancy. This process is theorized to be a development in maternal defense against extensive invasion of trophoblast cells. Trophoblasts are specialized cells that form the placenta and the peripheral cells of the blastocyst. During pregnancy, trophoblast invasion is vital to connect blood and nutrient flow to a developing fetus. As the invasion continues through the inner third of the myometrium, the maternal protective layer between the fetus and the mother's blood deteriorates. This mode of placentation is referred to as haemochorial placentation.

Other health consequences deriving from an unbalanced menses, or spontaneous decidualization prior to menses, include endometriosis, preeclampsia, and placenta accreta. Endometriosis is an often chronic condition that affects up to 10% of all women of reproductive age worldwide, possibly resulting in severe pelvic pain and infertility. Current treatments only ameliorate the symptoms of endometriosis rather than the root of the disease itself. A naturally occurring menstruation cycle in a rodent species has the potential to provide a valuable model for studying the physiological event and other menstruation-related disorders.

The sporadic appearance of blood at the vaginal openings of members of their spiny mouse colony prompted the team at the Hudson Institute of Medical Research to investigate. They used lavages to collect samples and confirm menstruation, with an average cycle ranging from 6 to 10 days. In addition to the follicular and luteal phases seen in rodents, the spiny mouse showed a third stage consistent with a menses cycle, characterized by an increase in red blood cells. Through histological staining, the thinning and growth of the endometrium was tracked and found to be in sync with the follicular and luteal phases, respectively, followed by degeneration of the corpus luteum and endometrial shedding. Investigators used a combination of histological and immunohistochemical findings to corroborate their physiological findings with hormonal changes in progesterone.

This discovery is unprecedented and researchers are calling for a more thorough examination of other spiny mice and related species to determine if menstruation has been overlooked in other mammals. The spiny mouse has a strong potential to transform the field of reproductive biology as a cost effective and natural model for menstruation that can answer long-standing questions about the etiology of endometriosis and related diseases.

Period1 Aug 2016

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