Identification of KIAA1210 as a novel X-chromosome-linked protein that localizes to the acrosome and associates with the ectoplasmic specialization in testes

Cell junctions are necessary for spermatogenesis, and there are numerous types of junctions intestis, such as blood-testis barrier, intercellular bridge, and ectoplasmic specialization (ES). Thedetails of their functions and construction are still unknown. To identify a novel protein essentialto the function of a cell junction, we enriched testis membrane protein and analyzed it using aproteomics approach. Here, we report a novel ES protein, which is encoded on the X chromosomeand an ortholog of hypothetical human protein KIAA1210. KIAA1210 is expressed in testis predominantly,localized to the sex body in spermatocyte, acrosome, and near ES. Moreover, KIAA1210possesses a topoisomerase 2 (TOP2)-associated protein PAT1 domain, a herpes simplex virus 1(HSV-1) large tegument protein UL36 hypothetical domain, and a provisional DNA translocase FtsKdomain. Using IP-proteomics with specific antibody to KIAA1210, we identified proteins includingTOP2 isoforms as components of a complex with KIAA1210, in cell junctions in testis. Theinteraction between KIAA1210 and TOP2 was confirmed by two different proteomic analyses. Furthermore,immunofluorescence showed that KIAA1210 and TOP2B co-localize around the sex bodyin spermatocyte, apical ES, and residual bodies in elongated spermatids. Our findings suggest that KIAA1210 may be essential cell junction protein that interacts with TOP2B to regulate the dynamicchange of chromatin structures during spermiogenesis.