Subfertility in mice harboring a mutation in βB2-crystallin

PURPOSE: βB2-crystallin is one of the most abundant proteins of the adult ocular lens of mammals although it is expressed at lower levels in several extralenticular locations. While mutations in βB2-crystallin are known to result in lens opacities, alterations in tissues besides the lens have not been previously investigated in these mutants. Since we found mice harboring the Crybb2(Phil) mutation bred poorly, here we assess the contribution of βB2-crystallin to mouse fertility and determine the expression pattern of βB2-crystallin in the testis. METHODS: The expression pattern of βB2-crystallin in the testis was analyzed by rt-PCR, western blotting, and immunohistochemistry. The fecundity of wildtype and Crybb2(Phil) mice was analyzed by quantitative fertility testing. The morphology of testes and ovaries was assessed by hematoxylin and eosin staining. RESULTS: In the mouse testis, βB2-crystallin mRNA is found at low levels at birth, but its expression upregulates in this tissue as the testis is primed to initiate spermatogenesis. Western blotting detected βB2-crystallin protein in sperm obtained from mice, cattle, and humans while immunolocalization detected this protein in developing sperm from the spermatocyte stage onward. Male and female mice homozygous for a 12 nucleotide inframe deletion mutation in βB2-crystallin are subfertile when analyzed on a Swiss Webster derived background due to defects in egg and sperm production. However, mice harboring the same mutation on the C57Bl/6 genetic background did not exhibit any defects in reproductive function. CONCLUSIONS: βB2-crystallin is expressed in developing and mature sperm and mice of both sexes harboring the Philly mutation in the βB2-crystallin gene are subfertile when analyzed on a Swiss Webster genetic background. While these data are suggestive of a role for βB2-crystallin in fertility, definitive determination of this will await the creation of a βB2-crystallin null mouse.