The balance between germ-line stem cell (GSC) self-renewal and differentiation in Drosophila ovaries is mediated by the antagonistic relationship between the Nanos (Nos)-Pumilio translational repressor complex, which promotes GSC self-renewal, and expression of Bam, a key differentiation factor. Here, we find that Bam and Nos proteins are expressed in reciprocal patterns in young germ cells. Repression of Nos in Bam-expressing cells depends on sequences in the nos 3-UTR, suggesting that Nos is regulated by translational repression. Ectopic Bam causes differentiation of GSCs, and this activity depends on the endogenous nos 3-UTR sequence. Previous evidence showed that Bgcn is an obligate factor for the ability of Bam to drive differentiation, and we now report that Bam forms a complex with Bgcn, a protein related to the RNA-interacting DExH-box polypeptides. Together, these observations suggest that Bam-Bgcn act together to antagonize Nos expression; thus, derepressing cystoblast-promoting factors. These findings emphasize the importance of translational repression in balancing stem cell self-renewal and differentiation.Drosophila ͉ germ cell ͉ oogenesis

The ␥ subunit of the Na,K-ATPase is a hydrophobic protein of approximately 10 kDa. The ␥ subunit was expressed in Sf-9 insect cells and Xenopus oocytes to ascertain its role in Na,K-ATPase function. Immunoblotting has shown that the ␥ subunit is expressed in Sf-9 cells infected with recombinant baculovirus containing the cDNA for the human ␥ subunit. Confocal microscopy demonstrates that the ␥ subunit can be delivered to the plasma membrane of Sf-9 cells independently of the other Na,K-ATPase subunits and that ␥ colocalizes with ␣1 when these proteins are coexpressed. When Sf-9 cells were coinfected with ␣1 and ␥, antibodies to the ␥ subunit were able to coimmunoprecipitate the ␣1 subunit, suggesting that ␥ is able to associate with ␣1. The ␥ subunit is a member of a family of single-pass transmembrane proteins that induces ion f luxes in Xenopus oocytes. Evidence that the ␥ subunit is a functional component was supported by experiments showing ␥-induced cation channel activity when expressed in oocytes and increases in Na ؉ and K ؉ uptake when expressed in Sf-9 cells.

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