Testis-Specific Cytochrome c-Null Mice Produce Functional Sperm but Undergo Early Testicular Atrophy

Abstract

Differentiating male germ cells express a testis-specific form of cytochrome c (Cyt c _T) that is distinct from the cytochrome c expressed in somatic cells (Cyt c _S). To examine the role of Cyt c _T in germ cells, we generated mice null for Cyt c _T. Homozygous Cyt c _T ^−/− pups were statistically underrepresented (21%) but developed normally and were fertile. However, spermatozoa isolated from the cauda epididymis of Cyt c _T-null animals were less effective in fertilizing oocytes in vitro and contain reduced levels of ATP compared to wild-type sperm. Sperm from Cyt c _T-null mice contained a greater number of immotile spermatozoa than did samples from control mice, i.e., 53.1% ± 13.7% versus 33.2% ± 10.3% (P < 0.0001) for vas deferens sperm and 40.1% ± 9.6% versus 33.2% ± 7.5% (P = 0.0104) for epididymal sperm. Cyt c _T-null mice often exhibit early atrophy of the testes after 4 months of age, losing germ cells as a result of increased apoptosis. However, no difference in the activation of caspase-3, -8, or -9 was detected between the Cyt c _T ^−/− testes and controls. Our data indicate that the Cyt c _T-null testes undergo early atrophy equivalent to that which occurs during aging as a consequence of a reduction in oxidative phosphorylation.

This work was supported in part by grants CA 42595 and HD 05863 from the National Institutes of Health.

We thank the Animal Facility at the Burnham Institute for mouse husbandry and Ling Wang of the Mouse Genetics Laboratory for IVF experiments.