Identification of genes expressed in Drosophila germline

在许多动物群体中，生殖系形成所需的因子定位于卵细胞浆中一个组织学上显著的区域，称为种质。在果蝇胚胎中，胚质位于后极区，并在极细胞中遗传，极细胞是这种动物的种系祖细胞。移植实验证明，胚质中含有足够形成种系能力的因子。胚质还含有指导腹部形成的第二局部活动。遗传分析揭示了一种共同的机制，指导腹部和种系形成因子的定位到后极。腹部形成的关键因素是纳米（nos）基因的产物。在这项研究中，我们发现nos在果蝇的种系形成中也是必不可少的。缺乏nos活性的极细胞不能成为功能性生殖细胞，因为它们不能迁移到性腺。在这些极细胞中，通常在性腺内启动的增强子激活在极细胞迁移期间过早开始。种系前体基因的过早激活可能导致这些细胞不能遵循正常的种系发育程序。此外，我们还发现了一种不可翻译的RNA，称为Pgc，它定位于种质中。大多数由表达反义Pgc RNA的雌性产生的胚胎中的极细胞不能完全迁移和填充胚胎性腺，并且从这些胚胎发育的雌性通常具有无配子卵巢。我们的结果支持Pgc RNA在种系发育中的重要作用。

In many animal groups, factors required for germline formation are localized in a histologically remarkable region in egg cytoplasm, called germ plasm. In Drosophila embryos, germ plasm is localized in the posterior pole region and is inherited in pole cells, the germ-line progenitors in this animal. Transplantation experiments have demonstrated that germ plasm contains factors with sufficient ability to form germ line. Germ plasm also contains a second localized activity that directs the formation of abdomen. Genetic analysis has revealed that a common mechanism directs the localization of the abdomen and germ-line forming factors to the posterior pole. The critical factor for abdomen formation is the product of the nanos (nos) gene.In this study, we show that nos is also esential for germ-line formation in Drosophila. Pole cells lacking nos activity are incapable of becoming functional germ cells because they fail to migrate into the gonads. In such pole cells, enhancer activation which normally initiates within the gonad begins prematurely during pole cell migration. Premature activation of genes in germline precursors may cause these cells to be incapable of following the normal germline developmental program.Furthermore, we have identified an untranslatable RNA,called Pgc, which is localized in germ plasm. Most pole cells in embryos produced by females expressing anti-sense Pgc RNA fail to complete migration and to populate the embryonic gonads, and females which develop from these embryos often have agametic ovaries. Our results support an essential role for Pgc RNA in germ line development.