Regulating gene expression in the Drosophila germ line.

Germ cells are the ultimate stem cells because they have the potential to give rise to a new organism. Specified during early embryogenesis in most species, germ cells evade somatic differentiation by using mechanisms such as transcriptional silencing and translational control (Seydoux and Braun 2006; Cinalli et al. 2008). To identify germ-line targets of translational regulation and to understand their mechanism of regulation, we used publicly available databases to identify RNAs localized to germ plasm. Using a transgenic reporter assay, we find that these germ-line RNAs are both spatially and temporally regulated during both oogenesis and embryogenesis by their 3'-untranslated regions (3'UTRs) (Rangan et al. 2008). We find that many RNAs that are spatially and temporally regulated in the early embryo are also translationally regulated during oogenesis. However, RNAs that are similarly regulated during oogenesis are no longer coregulated during embryogenesis, demonstrating that cis-acting sequences within a single RNA are used differentially during the life cycle of the germ line. Our study emphasizes a multifaceted role of translational regulation in germ cells. Many aspects of cellular behavior are shared between germ cells and other stem cells; thus, analysis of the translational regulatory networks controlling translation during the germ-line life cycle may reveal important general features of RNA regulation in stem cells.