Rat hdMutation Reveals an Essential Role of Centrobin in Spermatid Head Shaping and Assembly of the Head-Tail Coupling Apparatus1

The hypodactylous (hd) locus impairs limb development and spermatogenesis, leading to male infertility in rats. We show that the hdmutation is caused by an insertion of an endogenous retrovirus into intron 10 of the Cntrobgene. The retroviral insertion in hdmutant rats disrupts the normal splicing of Cntrobtranscripts and results in the expression of a truncated protein. During the final phase of spermiogenesis, centrobin localizes to the manchette, centrosome, and the marginal ring of the spermatid acroplaxome, where it interacts with keratin 5-containing intermediate filaments. Mutant spermatids show a defective acroplaxome marginal ring and separation of the centrosome from its normal attachment site of the nucleus. This separation correlates with a disruption of head-tail coupling apparatus, leading to spermatid decapitation during the final step of spermiogenesis and the absence of sperm in the epididymis. Cntrobmay represent a novel candidate gene for presently unexplained hereditary forms of teratozoospermia and the “easily decapitated sperm syndrome” in humans.