Expression of Dazl and Vasa in turtle embryos and ovaries: evidence for inductive specification of germ cells
Expression of Dazl and Vasa in turtle embryos and ovaries: evidence for inductive specification of germ cells
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DOI：
10.1111/j.1525-142x.2009.00360.x
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发表时间：
2009-09-01
影响因子：
2.9
通讯作者：
Johnson, Andrew D.
中科院分区：
文献类型：
--
作者：
Bachvarova, Rosemary F.;Crother, Brian I.;Johnson, Andrew D.
在双侧性动物中，生殖细胞由诱导/调节模式或预定（生殖质）模式指定。在四足动物中，哺乳动物和有尾目动物使用感应模式，而鸟类和无尾类动物使用预定模式。根据组织学数据，已经预测包括海龟在内的一些爬行动物使用感应模式。检查海龟卵母细胞，我们发现Dazl RNA，Vasa RNA和Vasa蛋白没有定位，表明种质不存在。如前所述，在体节阶段的海龟胚胎中，表达Dazl的原始生殖细胞（PGCs）位于从外侧后胚外内胚层通过肠道到性腺的路径上。在原肠胚中，表达Dazl的细胞出现在囊胚口板中，随后出现在囊胚口板下方，这表明PGCs是在相当于哺乳动物早期后原条的位置产生的。Vasa RNA在原肠胚至体节早期的体细胞中表达，Vasa RNA和蛋白质在后期胚胎的PGCs中表达。综上所述，证据有力地表明，海龟和其他爬行动物（蜥蜴）在胚胎中具有相同的PGCs位置，使用生殖细胞特化的诱导模式。现有证据的系统发育分析支持以下假设：（1）在爬行动物中，诱导模式是基础的，这表明这种模式在基础四足动物进化为四足动物时得到了维持;（2）预定模式在爬行动物中出现了两次;（3）诱导模式可能在几种鳞蜥类中使用，它们的PGC以一种不寻常的模式分布在胚胎周围。
In bilaterian animals, germ cells are specified by the inductive/regulative mode or the predetermined (germ plasm) mode. Among tetrapods, mammals and urodeles use the inductive mode, whereas birds and anurans use the predetermined mode. From histological data it has been predicted that some reptiles including turtles use the inductive mode. Examining turtle oocytes, we find that Dazl RNA, Vasa RNA, and Vasa protein are not localized, suggesting that germ plasm is not present. In turtle embryos at somite stages, primordial germ cells (PGCs) expressing Dazl lie on a path from the lateral posterior extraembryonic endoderm through the gut to the gonad as previously described. In gastrulating embryos, cells expressing Dazl are found in the blastoporal plate and subsequently below the blastoporal plate, indicating that PGCs are generated at the equivalent of the early posterior primitive streak of mammals. Vasa RNA is expressed in somatic cells of gastrula to early somite stages, and Vasa RNA and protein are expressed in PGCs of later embryos. Taken together the evidence strongly suggests that turtles, and other reptiles (lacertoid lizards) with the same location of PGCs in embryos, use the inductive mode of germ cell specification. Phylogenetic analysis of the available evidence supports the following hypotheses: (1) the inductive mode is basal among reptiles, indicating that this mode was maintained as basal tetrapods evolved to amniotes, (2) the predetermined mode arose twice within reptiles, and (3) the induced mode may be used in several lepidosaurs whose PGCs are located in an unusual pattern distributed around the embryo.