TSARG4 (testis and spermatogenesis-related gene 4 protein), also known as SPAG4L (sperm-associated antigen 4-like protein) or SRG4 (spermatogenesis-related gene 4) in mice, is a ubiquitously expressed protein in humans but, in mice, it is specifically expressed in the testis. TSARG4 belongs to the spindle pole body family of proteins and contains one Unc84/SUN domain and a potential transmembrane region. The human TSARG4 protein shares 74% amino acid identity with its mouse counterpart. In mice, TSARG4 is found in round spermatids and spermatocytes and may participate in mitosis. It has been hypothesized that TSARG4 localizes to the nuclear envelope.