Li Jing, Campbell Polly, Meyer Axel, Reznick David
Biology, University of Konstanz Department of Biology, Konstanz, Baden-Württemberg, Germany.
Department of Algal Development and Evolution, Max Planck Institute for Biology Tübingen, Tubingen, Baden-Württemberg, Germany.
Proc Biol Sci. 2025 Jul;292(2051):20250573. doi: 10.1098/rspb.2025.0573. Epub 2025 Jul 16.
Placentas evolved nine times in the fish family Poeciliidae. Each time, the egg follicle is the maternal contribution to the placenta. In non-placental species, the follicle fully provisions the egg before fertilization. In placental species, provisioning continues throughout development, and the follicle becomes a more elaborate, well-vascularized organ. We generated transcriptomes for follicles from yolking eggs and developing embryos from two pairs of closely related placental and non-placental species that represent independent origins of placentation plus one non-placental outgroup. We identified genes expressed in eggs but not embryos of non-placental species that continue to be expressed during embryonic development in placental species. Their functions include the maternal transfer of nutrients and immunity. We then reconstructed the ancestral state of the non-placental common ancestor of each species pair and identified genes that were either upregulated or downregulated in developing embryos of placental species relative to non-placental species. These include clusters associated with lipid metabolism, immune response and tissue structure. The two placental lineages were convergent in the function of these genes, but few genes were in common between them. Thus, diverse gene regulatory changes converge on shared essential functions in the independent origins of a complex trait.
胎盘在食蚊鱼科鱼类中独立进化了九次。每次进化时，卵泡都是胎盘的母体组成部分。在非胎盘物种中，卵泡在受精前为卵子提供全部营养。在胎盘物种中，营养供应在整个发育过程中持续进行，卵泡变成了一个更加精细、血管丰富的器官。我们从两对密切相关的胎盘物种和非胎盘物种（代表胎盘形成的独立起源）以及一个非胎盘外群的卵黄生成期卵子和发育中的胚胎中生成了卵泡转录组。我们鉴定出在非胎盘物种的卵子而非胚胎中表达、并在胎盘物种的胚胎发育过程中持续表达的基因。它们的功能包括母体营养物质传递和免疫。然后，我们重建了每个物种对的非胎盘共同祖先的原始状态，并鉴定出相对于非胎盘物种，在胎盘物种发育中的胚胎中上调或下调的基因。这些基因包括与脂质代谢、免疫反应和组织结构相关的基因簇。这两个胎盘谱系在这些基因的功能上趋同，但它们之间很少有共同的基因。因此，在一个复杂性状的独立起源过程中，不同的基因调控变化汇聚到共享的基本功能上。
