Wake-up-call, a lin-52 paralogue, and Always early, a lin-9 homologue physically interact, but have opposing functions in regulating testis-specific gene expression

A conserved multi-subunit complex (MybMuvB, MMB), regulates transcriptional activity of many different target genes in Drosophila somatic cells. A paralogous complex, tMAC, controls expression of at least 1500 genes in the male germline, and is essential for sperm production. The roles of specific subunits of tMAC, MMB or orthologous complexes in regulating target gene expression are not understood. MMB and orthologous complexes have Lin-52 as a subunit, but Lin-52 did not co-purify with tMAC. We identified wake-up-call (wuc), a lin-52 paralogue, via a physical interaction with the tMAC lin-9-related subunit Aly, and find that Wuc co-localises with known tMAC subunits. We show that wuc, like aly, is required for spermatogenesis. However, despite phenotypic similarities, the role of wuc is very different from that of previously characterised tMAC mutants. Unlike aly, loss of wuc results in only relatively mild defects in testis-specific gene expression. Strikingly, wuc loss of function partially rescues expression of target genes in aly mutant testes. We propose that wuc represses testis-specific gene expression, that this repression is counteracted by aly, and that aly and a testis-specific TF(II)D complex work together to promote high transcriptional activity of spermiogenic genes specifically in primary spermatocytes.