Identification of genes expressed in Drosophila germline

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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.