Regulation of Drosophila Vasa In Vivo through Paralogous Cullin-RING E3 Ligase Specificity Receptors

Abstract

In Drosophila species, molecular asymmetries guiding embryonic development are established maternally. Vasa, a DEAD-box RNA helicase, accumulates in the posterior pole plasm, where it is required for embryonic germ cell specification. Maintenance of Vasa at the posterior pole requires the deubiquitinating enzyme Fat facets, which protects Vasa from degradation. Here, we found that Gustavus (Gus) and Fsn, two ubiquitin Cullin-RING E3 ligase specificity receptors, bind to the same motif on Vasa through their paralogous B30.2/SPRY domains. Both Gus and Fsn accumulate in the pole plasm in a Vasa-dependent manner. Posterior Vasa accumulation is precocious in Fsn mutant oocytes; Fsn overexpression reduces ovarian Vasa levels, and embryos from Fsn-overexpressing females form fewer primordial germ cells (PGCs); thus, Fsn destabilizes Vasa. In contrast, endogenous Gus may promote Vasa activity in the pole plasm, as gus females produce embryos with fewer PGCs, and posterior accumulation of Vas is delayed in gus mutant oocytes that also lack one copy of cullin-5. We propose that Fsn- and Gus-containing E3 ligase complexes contribute to establishing a fine-tuned steady state of Vasa ubiquitination that influences the kinetics of posterior Vasa deployment.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank Bob Duronio, Niankun Liu, and Hong Han for antibodies, Beili Hu for the transgene injections, Maria Kilfoil for help with statistical analyses, the Murphy lab for the Drosophila gateway collection, and Chris Bazinet, Niankun Liu, and Paul MacDonald for sharing results prior to publication.

This work was supported by NICHD (R01HD036631) to P.L. and by the GRL Program (K20815000001) of KICOS/KMEST to B.-H.O.