Lochab Amaneet K, Extavour Cassandra G
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA; Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Dev Biol. 2017 Jul 15;427(2):258-269. doi: 10.1016/j.ydbio.2017.03.002. Epub 2017 Mar 8.
In multicellular organisms, the specification, maintenance, and transmission of the germ cell lineage to subsequent generations are critical processes that ensure species survival. A number of studies suggest that the Bone Morphogenetic Protein (BMP) pathway plays multiple roles in this cell lineage. We wished to use a comparative framework to examine the role of BMP signaling in regulating these processes, to determine if patterns would emerge that might shed light on the evolution of molecular mechanisms that may play germ cell-specific or other reproductive roles across species. To this end, here we review evidence to date from the literature supporting a role for BMP signaling in reproductive processes across Metazoa. We focus on germ line-specific processes, and separately consider somatic reproductive processes. We find that from primordial germ cell (PGC) induction to maintenance of PGC identity and gametogenesis, BMP signaling regulates these processes throughout embryonic development and adult life in multiple deuterostome and protostome clades. In well-studied model organisms, functional genetic evidence suggests that BMP signaling is required in the germ line across all life stages, with the exception of PGC specification in species that do not use inductive signaling to induce germ cell formation. The current evidence is consistent with the hypothesis that BMP signaling is ancestral in bilaterian inductive PGC specification. While BMP4 appears to be the most broadly employed ligand for the reproductive processes considered herein, we also noted evidence for sex-specific usage of different BMP ligands. In gametogenesis, BMP6 and BMP15 seem to have roles restricted to oogenesis, while BMP8 is restricted to spermatogenesis. We hypothesize that a BMP-based mechanism may have been recruited early in metazoan evolution to specify the germ line, and was subsequently co-opted for use in other germ line-specific and somatic reproductive processes. We suggest that if future studies assessing the function of the BMP pathway across extant species were to include a reproductive focus, that we would be likely to find continued evidence in favor of an ancient association between BMP signaling and the reproductive cell lineage in animals.
在多细胞生物中，生殖细胞谱系向后代的特化、维持和传递是确保物种生存的关键过程。多项研究表明，骨形态发生蛋白（BMP）信号通路在这一细胞谱系中发挥多种作用。我们希望利用一个比较框架来研究BMP信号在调节这些过程中的作用，以确定是否会出现一些模式，从而揭示可能在物种间发挥生殖细胞特异性或其他生殖作用的分子机制的进化。为此，我们在此回顾了迄今为止文献中支持BMP信号在后生动物生殖过程中发挥作用的证据。我们专注于生殖系特异性过程，并分别考虑体细胞生殖过程。我们发现，从原始生殖细胞（PGC）诱导到PGC身份的维持以及配子发生，BMP信号在多个后口动物和原口动物分支的整个胚胎发育和成年期调节这些过程。在经过充分研究的模式生物中，功能遗传学证据表明，除了那些不使用诱导信号来诱导生殖细胞形成的物种中的PGC特化外，BMP信号在所有生命阶段的生殖系中都是必需的。目前的证据与BMP信号在两侧对称动物诱导性PGC特化中是祖先特征这一假设一致。虽然BMP4似乎是本文所考虑的生殖过程中使用最广泛的配体，但我们也注意到不同BMP配体存在性别特异性使用的证据。在配子发生中，BMP6和BMP15似乎仅在卵子发生中起作用，而BMP8仅在精子发生中起作用。我们假设基于BMP的机制可能在动物进化早期就被用于特化生殖系，随后被用于其他生殖系特异性和体细胞生殖过程。我们认为，如果未来评估现存物种中BMP信号通路功能的研究以生殖为重点，我们很可能会继续发现支持BMP信号与动物生殖细胞谱系之间古老关联的证据。
