rasiRNAs, DNA Damage, and Embryonic Axis Specification

Abstract

Drosophila repeat-associated small interfering RNAs (rasiRNAs) have been implicated in retrotransposon and stellate locussilencing. However, mutations in the rasiRNA pathway genes armitage, spindle-E, and aubergine disrupt embryonic axisspecification, triggering defects in microtubule organization and localization of osk and grk mRNAs during oogenesis. Weshow that mutations in mei-41 and mnk, which encode ATR and Chk2 kinases that function in DNA damage signal transduction,dramatically suppress the cytoskeletal and RNA localization defects associated with rasiRNA mutations. In contrast, stellateand retrotransposon silencing are not restored in mei-41 and mnk double mutants. We also find that armitage, aubergine,and spindle-E mutations lead to germ-line-specific accumulation of γ-H2Av foci, which form at DNA double-strand breaks,and that mutations in armi lead to Chk2-dependent phosphorylation of Vasa, an RNA helicase required for axis specification.The Drosophila rasiRNA pathway thus appears to suppress DNA damage in the germ line, and mutations in this pathwayblock axis specification by activating an ATR/Chk2-dependent DNA damage response that disrupts microtubule polarizationand RNA localization.