Australian marsupials are facing a biodiversity crisis, requiring decisive action to prevent further extinction. Assisted Reproduction Technologies are a promising frontier in species conservation: however, while embryo culture methodologies have been developed for eutherian species, marsupial embryo culture has not yet been optimized. Given marsupial reliance on histotrophic nutrition, close examination of uterine fluid contents is necessary for optimizing embryo culture. Using a model marsupial, we have built a comprehensive molecular profile of the contents of the uterine lumen to understand exogenous cues regulating marsupial embryo development within the uterus.
Uteri from fat-tailed dunnarts (Sminthopsis crassicaudata) were collected each day of the 13.5-day long gestation, capturing every stage of in utero embryogenesis. Endometrial architecture was assessed using histological techniques, and uterine fluid was subjected to proteomic, metabolomic, and lipidomic profiling. Comparisons were drawn between each major stage of embryonic development, highlighting important metabolic pathways necessary for embryo development.
We showed that, in the dunnart, the uterine histotroph is provided by an extensive glandular network. The highly folded endometrial surface transformed across gestation, with adhesion zones between the endometrial epithelium and embryonic trophectoderm evident by day 12. Concurrently, the histotroph protein, metabolite, and lipid profile was altered post-adhesion. Prior to adhesion, when embryo is encased within a porous shell coat, each developmental stage had a unique molecular signature, indicating the dynamic maternal support driving embryogenesis prior to implantation.
It is evident that the marsupial uterus has evolved extensive glandular architecture and dynamic histotrophic cues to maximise the efficiency of their iconic reproductive strategy. The fat-tailed dunnart is an exquisite model for examining maternal-fetal communication and nutrient transfer, and comparative developmental biology. Insights from the molecular milieu presented here will be foundational to the development of marsupial assisted reproduction technologies necessary to combat the extreme rate of extinction faced by these species.