Splice variants of the SWR1-type nucleosome remodeling factor Domino have distinct functions during Drosophila melanogaster oogenesis
SWR1-type nucleosome remodeling factors replace histone H2A by variants to endow chromatin locally with specialized functionality. In Drosophila melanogaster a single H2A variant, H2A.V, combines functions of mammalian H2A.Z and H2A.X in transcription regulation and the DNA damage response. A major role in H2A.V incorporation for the only SWR1-like enzyme in flies, Domino, is assumed but not well documented in vivo. It is also unclear whether the two alternatively spliced isoforms, DOM-A and DOM-B, have redundant or specialized functions. Loss of both DOM isoforms compromises oogenesis, causing female sterility. We systematically explored roles of the two DOM isoforms during oogenesis using a cell type-specific knockdown approach. Despite their ubiquitous expression, DOM-A and DOM-B have non-redundant functions in germline and soma for egg formation. We show that chromatin incorporation of H2A.V in germline and somatic cells depends on DOM-B, whereas global incorporation in endoreplicating germline nurse cells appears to be independent of DOM. By contrast, DOM-A promotes the removal of H2A.V from stage 5 nurse cells. Remarkably, therefore, the two DOM isoforms have distinct functions in cell type-specific development and H2A.V exchange.