Supplementary tables. from Comparing the potential for maternal–fetal signalling in oviparous and viviparous lizards

The evolution of a placenta requires several steps including changing the timing of reproductive events, facilitating nutrient exchange, and the capacity for maternal–fetal communication. To understand the evolution of maternal–fetal communication, we used ligand-receptor gene expression as a proxy for the potential for cross-talk in a live-bearing lizard (Pseudemoia entrecasteauxii) and homologous tissues in a related egg-laying lizard (Lampropholis guichenotti). Approximately 70% of expressed ligand/receptor genes were shared by both species. Gene ontology (GO) analysis showed that there was no GO-enrichment in the fetal membranes of the egg-laying species, but live-bearing fetal tissues were significantly enriched for 50 GO-terms. Differences in enrichment suggest the evolution of viviparity involved reenforcing specific signalling pathways, perhaps to support fetal control of placentation. One identified change was in transforming growth factor beta signalling. Using immunohistochemistry, we show the production of the signalling molecule inhibin beta B occurs in viviparous fetal membranes but was absent in closely related egg-laying tissues, suggesting that the evolution of viviparity may have involved changes to signalling via this pathway. We argue that maternal–fetal signalling evolved through co-opting expressed signalling molecules and recruiting new signalling molecules to support the complex developmental changes required to support a fetus in utero.This article is part of the theme issue ‘Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom’.

胎盘的演化需历经多步核心进程，包括调整生殖事件的时序、促进营养交换，以及具备母胎信号通信的能力。为解析母胎通信的演化机制，我们以配体-受体（ligand-receptor）基因表达作为跨细胞信号串扰潜力的替代指标，分别研究了胎生蜥蜴（*Pseudemoia entrecasteauxii*）及其近缘卵生蜥蜴（*Lampropholis guichenotti*）的同源组织。两个物种共表达的配体-受体基因占比约70%。基因本体（Gene Ontology, GO）富集分析结果显示，卵生物种的胎膜未出现GO功能富集，而胎生物种的胎儿组织则显著富集了50个GO术语。富集程度的差异表明，胎生性状的演化涉及特定信号通路的强化，这或许是为了支持胎儿对胎盘形成的调控。研究发现的一处关键变化发生在转化生长因子β（transforming growth factor beta）信号通路中。通过免疫组织化学（immunohistochemistry）实验，我们证实胎生物种的胎膜可产生信号分子抑制素βB（inhibin beta B），而近缘卵生物种的对应组织中并无该分子的表达，这提示胎生的演化或许涉及该信号通路的调控变化。我们认为，母胎信号通信的演化是通过复用已表达的信号分子，并招募新的信号分子，以支撑子宫内胎儿发育所需的复杂生理重构。本文隶属于专题“胚外组织：探索动物界的概念、定义与功能”。