Kulkarni Arpita, 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.
Stem Cell Res. 2017 Oct;24:188-194. doi: 10.1016/j.scr.2017.07.018. Epub 2017 Jul 19.
Germ cells have been considered "the ultimate stem cell" because they alone, during normal development of sexually reproducing organisms, are able to give rise to all organismal cell types. Morphological descriptions of a specialized cytoplasm termed 'germ plasm' and associated electron dense ribonucleoprotein (RNP) structures called 'germ granules' within germ cells date back as early as the 1800s. Both germ plasm and germ granules are implicated in germ line specification across metazoans. However, at a molecular level, little is currently understood about the molecular mechanisms that assemble these entities in germ cells. The discovery that in some animals, the gene products of a small number of lineage-specific genes initiate the assembly (also termed nucleation) of germ granules and/or germ plasm is the first step towards facilitating a better understanding of these complex biological processes. Here, we draw on research spanning over 100years that supports the hypothesis that these nucleator genes may have evolved convergently, allowing them to perform analogous roles across animal lineages.
生殖细胞被认为是“终极干细胞”，因为在有性生殖生物的正常发育过程中，只有它们能够产生所有的机体细胞类型。早在19世纪，人们就对生殖细胞内一种称为“生殖质”的特殊细胞质以及相关的电子致密核糖核蛋白（RNP）结构“生殖颗粒”进行了形态学描述。生殖质和生殖颗粒都与后生动物的生殖系特化有关。然而，目前在分子水平上，对于在生殖细胞中组装这些实体的分子机制了解甚少。在一些动物中发现少数谱系特异性基因的基因产物启动了生殖颗粒和/或生殖质的组装（也称为成核），这是朝着更好地理解这些复杂生物过程迈出的第一步。在这里，我们借鉴了100多年来的研究，这些研究支持这样一种假说，即这些成核基因可能是趋同进化的，从而使它们能够在动物谱系中发挥类似的作用。
