Calcium Binding Protein, Spermatid Specific 1 (CABS1)

CABS1 is a novel calcium-binding protein specifically expressed in elongate spermatids of mice. The changes of the protein contents in testis during these processes were analyzed by two-dimensional gel electrophoresis in order to identify the proteins expressed at the specific stages of spermatogenesis. An acidic protein that disappeared and recovered in the same time course as spermatids after the busulfan treatment was identified as CABS1 by mass spectrometry. It was found that CABS1 was specifically expressed in the elongate spermatids at steps 13 to 16 in stages I to VIII of the seminiferous epithelium cycle of the mouse, and then it localized to the principal piece of flagellum of the mature sperm in the cauda epididymis. CABS1 is a calcium-binding protein that binds calcium during the maturation in the epididymis.