Meeting Abstract
The expression of the pituitary hormone prolactin (PRL) is well documented in the placental tissues of pregnant therian mammals. While its exact role in supporting pregnancy is unclear, genomic studies of the prolactin locus during pregnancy have unveiled variation in copy number and placenta-specific transposon-derived promoters, hinting at a critical role. Further, it is unknown whether PRL is expressed at the maternal-fetal interface of other viviparous vertebrates. Here we study Poeciliopsis, a unique genus of live-bearing fish that have evolved bonafide placental structures at least three times independently, providing a unique opportunity to study the de novo evolution of placentation. The placentas of these fish contain a maternal follicle component and a fetal component, respectively akin to the decidua and trophoblast of eutherian mammals. We have been surprised to find the expression of fetal and maternal mammalian placenta markers in these fish. Recently, we found expression of PRL in the maternal follicle of Poeciliopsis turneri, Poeciliopsis retropinna, and Poeciliopsis prolifica, each species representing an independent evolution of placentation. Furthermore, we find no PRL expression in the maternal follicle of Poeciliopsis gracilis, a non-placental member of this genus. This suggests that PRL has been independently co-opted for placental function within Poeciliopsis multiple times. We are currently investigating whether the expression pattern of the two prolactin genes in Poeciliopsis, Prl and Prl2, differs and if the promoter structure of placental prolactin transcripts is similar to mammalian prolactins. In completing this work we aim to expand our knowledge of prolactin’s role in the evolution of pregnancy.
