Conserved RNA helicase Vasa regulates ribonucleoprotein condensate dynamics and mRNA localization.

Germ granules are germline ribonucleoprotein condensates that concentrate proteins and mRNAs essential for animal development. Although the DEAD-box RNA helicase Vasa is a conserved core germ granule component, its role within these condensates remains poorly understood. Using Drosophila and human cell systems, we showed that condensation of Oskar (Osk), the fly germ granule nucleator, occurred independently of Vasa. However, in late oocytes lacking Vasa, Osk-eGFP formed aggregates and exhibited markedly reduced exchange with the aggregate surroundings. Consistently, Vasa increased Osk-eGFP condensate recovery in cells. Additionally, mRNA localization to germ granules was not persistent in oocytes lacking Vasa, while in cells, co-expression of Vasa and Osk was necessary and sufficient for mRNA localization to condensates. Notably, localization of nanos messenger ribonucleoprotein (mRNP) to condensates reduced Vasa-dependent enhancement of Osk-eGFP exchange. Together, our study reveals the DEAD-box RNA helicase Vasa as a central regulator of condensate dynamics and mRNP localization in vivo and in cellulo.