Rhophilin, a small GTPase Rho-binding protein, is abundantly expressed in the mouse testis and localized in the principal piece of the sperm tail.

Tissue distribution and cellular localization of rhophilin, a 71 kDa Rho-binding protein, were examined in mice. Rhophilin mRNA was highly expressed in adult testis, but was absent in the testis of W/WV mice deficient in germ cells. An anti-rhophilin antibody detected a band of an expected size in sperm extracts, which was enriched in the tail fraction. Immunofluorescence analysis revealed two lines of striated staining running in parallel in the principal piece of the sperm tail. These results suggest that rhophilin is expressed in germ cells and localized in the fibrous sheath of the sperm tail.