Testis-specic protein that plays an important role in fusion of proacrosomal vesicles and perinuclear theca formation. Interacts with ACTL7A. Localizes predominantly in the equatorial segment of the sperm head and neck regions, with some localization in the acrosomal segment of the head. Colocalizes in the acrosomal and equatorial segments of sperm with ACTL7A. Colocalizes with PLCZ1 in the equatorial segment of the head of capacitated sperm. Belongs to the actin family.