Abstract
In Drosophila melanogaster, primordial germ cells are specified at the posterior pole of the very early embryo. This process is regulated by the posterior localized germ plasm that contains a large number of RNAs of maternal origin. Transcription in the primordial germ cells is actively down-regulated until germ cell fate is established. Bulk expression of the zygotic genes commences concomitantly with the degradation of the maternal transcripts. Thus, during embryogenesis, maternally provided and zygotically transcribed mRNAs determine germ cell development collectively. In an effort to identify novel genes involved in the regulation of germ cell behavior, we carried out a large-scale RNAi screen targeting both maternal and zygotic components of the embryonic germ line transcriptome. We identified 48 genes necessary for distinct stages in germ cell development. We found pebble and fascetto to be essential for germ cell migration and germ cell division, respectively. Our data uncover a previously unanticipated role of mei-P26 in maintenance of embryonic germ cell fate. We also performed systematic co-RNAi experiments, through which we found a low rate of functional redundancy among homologous gene pairs. As our data indicate a high degree of evolutionary conservation in genetic regulation of germ cell development, they are likely to provide valuable insights into the biology of the germ line in general.
Highlights
The fruit fly, Drosophila melanogaster, provides a powerful experimental model system for the genetic dissection and in vivo analysis of germ cell totipotency
We used the in situ hybridization data of the BDGP and fly-FISH databases and microarray data on separated germ cells to assemble a list of genes expressed in the germ-line at any stage of embryonic development [16,17,18]
Germ cell development in dsRNA-treated embryos was recorded throughout embryogenesis and the movies were analyzed by visual inspection (Figure 1A–D, Movie S1)
Summary
The fruit fly, Drosophila melanogaster, provides a powerful experimental model system for the genetic dissection and in vivo analysis of germ cell totipotency. At the onset of Drosophila embryogenesis, primordial germ cells (PGCs) bud at the posterior pole of the syncytial embryo. By their formation, PGCs incorporate a specialized cytoplasm, the so-called germ plasm, which contains maternally provided transcripts and proteins [1]. PGC-enriched maternal transcripts and proteins involve stem cell proliferation regulators, such as mei-P26, reflecting the importance of proliferation control in PGC development [2]. After their formation, PGCs attach to the underlying midgut anlage and are passively transported into the midgut primordium. Sexual identity of the germ cells is determined, and embryonic testes and ovaries are established [4]
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