Mice that are homozygous for the targeted mutation are viable, normal in size and do not display any gross physical or behavioral abnormalities. Homozygous male mice are sterile due to arrested spermatogenesis at the late meiosis, primary spermatocyte stage. Female homozygotes are fertile. No gene product (mRNA) was detectable by semiquantitative RT-PCR analysis of peripheral nerve. Embryonic testis development is impaired. By six weeks of age, the mass of testes from homozygous males is 90% smaller than testes from heterozygous males. Histological examination reveals a diminished number of germ cells and no mature sperm in the testis or epididymis. Peripheral nerves from mutant mice appear flattened with structurally disorganized protective sheaths. The perineural cells, glia and mesenchymal cells, develop defective tight junctions, causing the perineurium to be permeable. This mutant mouse strain may be useful in studies related to male sterility and regulation of peripheral nerve development. The Jackson Laboratory 2024, used with permission.