Chigno/CG11180 and SUMO are Chinmo-Interacting Proteins with a Role in Drosophila Testes Stem Cells

Maintenance of sexual identity on the cellular level ensures the proper function of sexually dimorphic genes expressed in the brain and gonads. Disruption of genes that regulate sex maintenance alters the cellular structure of these tissues and leads to infertility and diseases, such as diabetes, obesity, and gonadal cancers. Sex maintenance in the testis of Drosophila melanogaster depends on the previously identified gene chinmo (Chronologically inappropriate morphogenesis). Chinmo’s effect on testis differentiation has been investigated in detail, but there is still much to be elucidated about its structure, function, and interactions with other proteins. Using a two-hybrid screen, we find that Chinmo interacts with itself, the small ubiquitin-like modifier SUMO, the novel protein CG11180, and four other proteins (CG4318, Ova (Ovaries absent), Taf3 (TBP-associated factor 3), and CG18269). Since both Chinmo and CG11180 contain sumoylation sites and SUMO-interacting motifs (SIMs), we analyzed their interaction in more detail. Using site-directed mutagenesis of a unique SIM in CG11180, we demonstrate that Chinmo’s interaction with CG11180 is SUMOdependent. Furthermore, to assess the functional relevance of both SUMO and CG11180, we performed RNAi-mediated knockdown of both proteins in somatic cells of the Drosophila testis. Using this approach, we find that CG11180 and SUMO are required in somatic cells of adult testes, and that reduction of either protein causes formation of germ cell tumors. Overall, our work indicates that SUMO functionally links Chinmo and CG11180 in somatic cells of the adult Drosophila testis. Consistent with the CG11180 knockdown phenotype in male testes, and to underscore its connection to Chinmo, we propose the name Childless Gambino (Chigno) for CG11180.