The study of disorders of pregnancy and menstruation has been hampered by the fact that most commonly used laboratory animal models, such as mice, don’t menstruate. In fact, menstruation is incredibly rare in nature and is largely restricted to higher-order primates such as gorillas, orang-utans and humans; a mere 1.5% of the 5,502 known mammalian species.
The study of disorders of pregnancy and menstruation has been hampered by the fact that most commonly used laboratory animal models, such as mice, don’t menstruate. In fact, menstruation is incredibly rare in nature and is largely restricted to higher-order primates such as gorillas, orang-utans and humans; a mere 1.5% of the 5,502 known mammalian species.
However, researchers at Monash University and Hudson Institute of Medical Research discovered that a tiny rodent known as the Egyptian spiny mouse (Acomys cahirinus) exhibits cyclical, human-like menstruation. This discovery, published in 2017, represented a game-changing breakthrough for studying female reproductive health. The team has now published new research providing more detail about early pregnancy in this fascinating species.
The team showed some fascinating similarities and differences to humans in terms of ovulation and embryo implantation. They showed that spiny mice are capable of ovulating and getting pregnant soon after they have given birth and when they are lactating. This is unlike the situation in humans where breastfeeding prevents ovulation for around 6 months. Spiny mouse embryos also don’t embed as deeply in the uterine endometrium, suggesting they may not experience the same hormonal control of ovulation and embryo implantation seen in humans.
Surprisingly though, spiny mouse early pregnancy involves the formation and remodelling of endometrial spiral arteries that are observed in menstrual species such as humans. These coiled, spring-like arteries act as shock absorbers for the growing embryo and directly provide the placenta with blood flow. Inadequate formation or remodelling of these arteries can lead to major pregnancy complications such as preeclampsia or intrauterine growth restriction (IUGR). The spiny mouse model could be used to give unique insights into how these arteries form and how their dysfunction could lead to pregnancy complications.
Overall, the research revealed that spiny mice appear to be a ‘pick and mix’ of reproductive characteristics from both rodents and primates, and that spiny mice undergo similar uterine remodelling around the time of embryo implantation as menstruating species. The authors hope this study will guide future studies in this species to provide new insights into pathologies and treatment options for pregnancy disorders such as IUGR and preeclampsia.
Written by Jarrod McKenna and Liza O’Donnell