Role of ßB2-Crystallin in Fertility

Abstract

Abstract: : Purpose: It is well established that α-crystallins are expressed in nonlens tissue and function as molecular chaperones. However, while the ß/γ crystallins are present in nonlens tissues, their non-refractive functions are unidentified. ßB2-crystallin is a major water-soluble protein found in the adult ocular lens and the mutation of this gene results in autosomal dominant cataract. While investigating mice homozygous for the Crybb2^Phil mutation, we observed that they produce infrequent, small litters, in contrast to the background strain. Methods: Quantitative fertility tests and sperm function assays were performed to calculate differences between litter sizes, fecundity, sperm count and sperm motility of Swiss-Webster and Crybb2^Phil homozygous mice. Furthermore, light microscopy and SEM were used to study morphological differences in sperm, testis and ovary. RT-PCR and western analysis were performed to determine the expression of ßB2-crystallin in reproductive tissues. Results: Swiss-Webster matings produced litters of 12.7 + 2.5 pups, and had a fecundity of 12.8 + 4.0 pups per 30 day period. However, Crybb2^Phil homozygous males mated with Swiss-Webster females produced litters of 9.5 + 3.4 pups, and had a fecundity of 5.4 + 4.2 pups per 30 day period. Additionally, Crybb2^Phil homozygous females mated w­­­­ith Swiss-Webster males resulted in litters of 7.9 + 2.0 pups, and had a fecundity of 4.4 + 4.0 pups per 30 day period. Preliminary sperm function assays suggest significant differences in sperm count and motility. However, SEM did not show any morphological differences in sperm structure. The ßB2-crystallin protein was detected in the ovaries of mice and sperm of mice, bulls and humans. The ßB2-crystallin mRNA was expressed in the ovary and testis of mice. Developmental RT-PCR of the testis reveals the presence of ßB2-crystallin mRNA at day 1 before spermatogenesis begins, with a large upregulation of expression between day 15 and 17 corresponding to the onset of meiosis. Conclusion: Both male and female Crybb2^Phil homozygous mice are subfertile; and this subfertility is autosomal recessive. Thus, ßB2-crystallin is likely to be important for male and female fertility, and may play a role in sperm function.

Keywords: crystallins • protein structure/function • mutations