Extracellular domain of V-set and immunoglobulin domain containing 1 (VSIG1) interacts with sertoli cell membrane protein, while its PDZ-binding motif forms a complex with ZO-1.

V-set and immunoglobulin domain containing 1 (VSIG1) is a newly discovered member of the junctional adhesion molecule (JAM) family; it is encoded by a gene located on human chromosome X and preferentially expressed in a variety of cancers in humans. Little is known about its physiological function. To determine the role(s) of VSIG1 in mammalian spermatogenesis, we first generated a specific antibody against mouse VSIG1 and examined the presence and localization of the protein in tissues. RTRCR and Western blot analysis of the mouse tissues indicated that VSIG1 was specifically expressed in the testis. Furthermore, the results of our trypsinization and biotinylation assays strongly support the assumption that VSIG1 is localized on the testicular germ cell surface. In order to determine whether VSIG1 is capable of participation in homotypic interactions, we performed a GST-pull down assay by using recombinant GST-fusion and Histagging proteins. The pull-down assay revealed that each GST-fusion Ig-like domain shows homotypic binding. We further show that mVSIG1 can adhere to the Sertoli cells through its first Ig-like domain. To identify the protein that interacted with cytoplasmic domain, we next performed co-immunoprecipitation analysis. This analysis showed that ZO-1, which is the central structural protein of the tight junction, is the binding partner of the cytoplasmic domain of mouse VSIG1. Our findings suggest that mouse VSIG1 interacts with Sertoli cells by heterophilic adhesion via its first Ig-like domain. In addition, its cytoplasmic domain is critical for binding to ZO-1.