Red-rumped agouti (Dasyprocta leporina linnaeus, 1758) yolk sac development during the early gestation stage

Phylogenetically, the yolk sac is an ancient structure in vertebrate evolution and crucial in the placentation of viviparous animals, playing an essential role in embryogenesis. Considering that the yolk sac persists until birth in rodents, forming an active placenta, this study aimed to describe the yolk sac development process in red-rumped agoutis (Dasyprocta leporina) during the early gestation phase and associating the progression to morphological changes in other structures. To this end, six female red-rumped agoutis obtained from CEMAS-UFERSA were monitored for 24 h. The first gestation day was defined as 24 h post-copulation. Samplings were carried out on the 13th, 14th and 15th pregnancy days. Pregnant uteri were fixed in 8% paraformaldehyde for 72 h and histologically processed, with 5 μm sections stained with Hematoxylin-Eosin (HE) and analyzed under a light microscope. On the 13th day, the blastocyst is implanted on the antimesometrial side of the uterus, surrounded by uterine stromal cells organizing themselves around this structure. On the 14th day, the intramural wall between the uterus and the embryo begins to break down and the parietal yolk sac exhibits spindle cells, while the visceral yolk sac presents eosinophilic cuboidal cells. On the 15th day, the intramural layer is almost completely ruptured, revealing a vascular bed between the embryo and the decidua. The visceral yolk sac did not yet contain its characteristic villi at this stage. Blastocyst formation and yolk sac differentiation take place between the 13th and 15th pregnancy days. The yolk sac inversion process is also described, taking place between the 14th and 15th gestation days, which had not yet been documented for red-rumped agoutis.