VCP acts downstream of tTAFs to downregulate mono-ubiquitinated H2A and promote spermatocyte differentiation in Drosophila

Valosin-containing protein (VCP) binds and extracts ubiquitinated cargo to regulate protein homeostasis. While VCP has been studied primarily in aging and disease contexts, it also affects germline development. However, the precise molecular functions of VCP in the germline, particularly in males, are poorly understood. Using the Drosophila male germline as a model system, we find that VCP translocates from the cytosol to the nucleus as germ cells transition into the meiotic spermatocyte stage. Importantly, nuclear translocation of VCP appears to be one critical event stimulated by testis-specific TBP-associated factors (tTAFs) to drive spermatocyte differentiation. Like tTAF mutants, spermatocyte gene expression fails to properly activate in VCP-RNAi testes, and germ cells arrest in early meiosis. At a molecular level, VCP activity supports spermatocyte gene expression by downregulating a repressive histone modification, mono-ubiquitinated H2A (H2Aub), at this developmental transition. Remarkably, experimentally blocking H2Aub in VCP-RNAi testes is sufficient to overcome the meiotic-arrest phenotype and to promote development through meiosis. Collectively, our data highlight VCP as a novel downstream effector of tTAFs that downregulates H2Aub to facilitate meiotic progression. SUMMARY STATEMENT VCP promotes the downregulation of mono-ubiquitinated H2A (H2Aub), potentially by driving H2A turnover. VCP-dependent downregulation of H2Aub occurs downstream of testis-specific TBP-associated factors and supports spermatocyte gene expression and differentiation.