Meeting Abstract
Placentation evolved many times independently in vertebrates, and while the core functions of all placentas are similar we know less about how this similarity extends to the molecular level. Here we study Poeciliopsis, a unique genus of live-bearing fish that have evolved placental structures at least three times independently. The maternal follicle is a key component of these structures; it envelops yolk rich eggs and is morphologically simple in non-placental species, but has elaborate villous structures in placental species. Through sequencing the follicle transcriptome of a placental, P. retropinna, and non-placental, P. turrubarensis, species we found genes known to be critical for placenta function expressed in both species despite their difference in complexity. Additionally, when we compare the transcriptome of different river populations of P. retropinna, known to vary in maternal provisioning, we find differential expression of secretory genes expressed specifically in the top layer of villi cells in the maternal follicle. This provides some of the first evidence that the placental structures of Poeciliopsis function using a secretory mechanism rather than direct exchange between maternal-fetal circulation. Finally, when we look at the expression of placenta proteins at the maternal-fetal interface of a larger sampling of Poeciliopsis species we find expression of key maternal and fetal placenta proteins in their cognate tissue types of all species, but follicle expression of Prolactin is restricted to only placental species. Taken together, we suggest that all Poeciliopsis follicles are poised for placenta function, but require expression of key genes to form secretory villi.
