Histone acetyltransferase Enok regulates oocyte polarization by promoting expression of the actin nucleation factor spire

KAT6 histone acetyltransferases (HATs) are highly conserved in eukaryotes and have been shown to play important roles in transcriptional regulation. Here, we demonstrate that the Drosophila KAT6 Enok acetylates histone H3 Lys 23 (H3K23) in vitro and in vivo. Mutants lacking functional Enok exhibited defects in the localization of Oskar (Osk) to the posterior end of the oocyte, resulting in loss of germline formation and abdominal segments in the embryo. RNA sequencing (RNA-seq) analysis revealed that spire (spir) and maelstrom (mael), both required for the posterior localization of Osk in the oocyte, were down-regulated in enok mutants. Chromatin immunoprecipitation showed that Enok is localized to and acetylates H3K23 at the spir and mael genes. Furthermore, Gal4-driven expression of spir in the germline can largely rescue the defective Osk localization in enok mutant ovaries. Our results suggest that the Enok-mediated H3K23 acetylation (H3K23Ac) promotes the expression of spir, providing a specific mechanism linking oocyte polarization to histone modification.