Department of Biological Science, Macquarie University, Sydney, New South Wales, Australia.
J Morphol. 2021 Jul;282(7):1047-1053. doi: 10.1002/jmor.21322. Epub 2021 Jan 18.
Organ development occurs through the coordinated interaction of distinct tissue types. So, a question at the core of understanding the evolution of new organs is, how do new tissue-tissue signalling networks arise? The placenta is a great model for understanding the evolution of new organs, because placentas have evolved repeatedly, evolved relatively recently in some lineages, and exhibit intermediate forms in extant clades. Placentas, like other organs, form from the interaction of two distinct tissues, one maternal and one fetal. If each of these tissues produces signals that can be received by the other, then the apposition of these tissues is likely to result in new signalling dynamics that can be used as a scaffold to support placenta development. Using published data and examples, in this review I demonstrate that placentas are derived from hormonally active organs, that considerable signalling potential exists between maternal and fetal tissues in egg-laying vertebrates, that this signalling potential is conserved through the oviparity-viviparity transition, and that consequences of these interactions form the basis of derived aspects of placentation including embryo implantation. I argue that the interaction of placental tissues, is not merely a consequence of placenta formation, but that novel interactions form the basis of new placental regulatory networks, functions, and patterning mechanisms.
器官的发生发展是通过不同组织类型的协调相互作用来实现的。因此，理解新器官进化的核心问题是，新的组织-组织信号网络是如何产生的？胎盘是理解新器官进化的一个很好的模型，因为胎盘已经多次进化，在一些谱系中相对较新，并且在现存的进化枝中表现出中间形式。胎盘和其他器官一样，是由两种不同的组织——母体组织和胎儿组织——相互作用形成的。如果这些组织中的每一个都能产生可以被另一个组织接收的信号，那么这些组织的并置很可能会产生新的信号动态，这些信号动态可以作为支持胎盘发育的支架。在这篇综述中，我使用已发表的数据和例子证明，胎盘是由具有激素活性的器官衍生而来的，在卵生脊椎动物中，母体和胎儿组织之间存在相当大的信号潜力，这种信号潜力在卵生动物向胎生动物的过渡中得以保留，并且这些相互作用的结果构成了胎盘发生的衍生方面的基础，包括胚胎着床。我认为，胎盘组织的相互作用不仅仅是胎盘形成的结果，而是新的相互作用构成了新的胎盘调节网络、功能和模式形成机制的基础。
