AUTHOR=Adashev Vladimir E. , Kotov Alexei A. , Bazylev Sergei S. , Kombarov Ilia A. , Olenkina Oxana M. , Shatskikh Aleksei S. , Olenina Ludmila V. 

TITLE=Essential functions of RNA helicase Vasa in maintaining germline stem cells and piRNA-guided Stellate silencing in Drosophila spermatogenesis

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2024.1450227

DOI=10.3389/fcell.2024.1450227

ISSN=2296-634X

ABSTRACT=<p>DEAD-box RNA helicase Vasa is required for gonad development and fertility in multiple animals. Vasa is implicated in many crucial aspects of <italic>Drosophila</italic> oogenesis, including translation regulation, primordial germ cell specification, piRNA silencing of transposable elements, and maintenance of germline stem cells (GSCs). However, data about Vasa functions in <italic>Drosophila</italic> spermatogenesis remain controversial. Here we showed that loss-of-function <italic>vasa</italic> mutations led to failures of GSC maintenance in the testes, a severe loss of total germ cell content, and a cessation of male fertility over time. Defects in GSC maintenance in <italic>vasa</italic> mutant testes were not associated with an increasing frequency of programmed cell death, indicating that a premature loss of GSCs occurred <italic>via</italic> entering differentiation. We found that Vasa is implicated in the positive regulation of <italic>rhino</italic> expression both in the testes and ovaries. The introduction of a transgene copy of <italic>rhino</italic>, encoding a nuclear component of piRNA pathway machinery, in <italic>vasa</italic> mutant background allowed us to restore premeiotic stages of spermatogenesis, including the maintenance of GSCs and the development of spermatogonia and spermatocytes. However, piRNA-guided repression of <italic>Stellate</italic> genes in spermatocytes of <italic>vasa</italic> mutant testes with additional <italic>rhino</italic> copy was not restored, and male fertility was disrupted. Our study uncovered a novel mechanistic link involving Vasa and Rhino in a regulatory network that mediates GSC maintenance but is dispensable for the perfect biogenesis of <italic>Su(Ste)</italic> piRNAs in testes. Thus, we have shown that Vasa functions in spermatogenesis are essential at two distinct developmental stages: in GSCs for their maintenance and in spermatocytes for piRNA-mediated silencing of <italic>Stellate</italic> genes.</p>