Placentation evolved many times independently in vertebrates. 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 independently evolved complex placental structures at least three times. The maternal follicle is a key component of these structures. It envelops yolk rich eggs and is morphologically simple in lecithotrophic species, but has elaborate villous structures in matrotrophic species. Through sequencing the follicle transcriptome of a matrotrophic, P. retropinna, and lecithotrophic, 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 contact with maternal 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 matrotrophic species. Taken together, we suggest that all Poeciliopsis follicles are poised for placenta function, but require expression of key genes to form secretory villi.

中文翻译：

---

浮萍产妇卵泡中发现的胎盘和分泌的分子标志。

胎盘在脊椎动物中独立地进化了许多次。尽管所有胎盘的核心功能相似，但我们对这种相似性如何扩展到分子水平的了解较少。在这里，我们研究古生鱼（Poeciliopsis），这是一种独特的活体鱼类，已经独立进化了至少三倍的复杂胎盘结构。产妇卵泡是这些结构的关键组成部分。它包裹着卵黄丰富的卵，在营养营养的物种中形态简单，但是在营养营养的物种中具有复杂的绒毛结构。通过对自养营养性逆向疟原虫和卵营养性抗逆转录病毒P. turrubarensis的卵泡转录组进行测序，我们发现了已知的基因，尽管在复杂性上存在差异，但在这两个物种中表达的胎盘功能至关重要。另外，当我们比较已知在母体供应中有所不同的P. retropinna的不同河流种群的转录组时，我们发现了分泌基因的差异表达，这些基因在母体卵泡的绒毛细胞的顶层特别表达。这提供了一些最初的证据，表明痘苗病的胎盘结构是利用分泌机制而不是直接与母体循环接触而起作用。最后，当我们在大量样本的产妇和胎儿的胎盘界面上观察胎盘蛋白的表达时，我们发现所有种类的同源组织类型中关键的母胎盘蛋白的表达，但是催乳素的卵泡表达是仅限于自养物种。综上所述，我们建议所有Poeciliopsis卵泡均具有胎盘功能，