Identification of genes expressed in Drosophila germline

在许多动物群体中，形成生殖系所需的因子定位于卵细胞质中一个组织学上显著的区域，称为种质。在果蝇胚胎中，种质定位于后极区，并在极细胞中遗传，极细胞是这种动物的生殖系祖细胞。移植实验证明，种质中含有足以形成种系的因子。生殖质还包含第二种局部活动，指导腹部的形成。遗传分析揭示了一种共同的机制，即将腹部和胚系形成因素的定位定向到后极。腹部形成的关键因素是纳米(Nos)基因的产物。在这项研究中，我们证明了nos对果蝇生殖系的形成也是必不可少的。缺乏一氧化氮合酶活性的极细胞无法成为有功能的生殖细胞，因为它们无法迁移到性腺中。在这种极细胞中，通常在性腺内启动的增强子激活在极细胞迁移过程中过早地开始。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，我们还发现了一种定位于种质中的不可翻译的RNA，称为PGC。在表达反义PGC RNA的雌性胚胎中，大多数极细胞无法完成迁移并填充到胚胎性腺中，从这些胚胎发育而来的雌性通常具有无融合生殖的卵巢。我们的结果支持PGC RNA在生殖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.