Male hybrid sterility of mice with the genomic region of the Kit(W) mutation and the Kit(S) allele from Mus spretus

Two congenic strains, C57BL-Kit(w) and C57BL-Kit(s), were generated. The Ki t(w) allele originated from strain WB-Kit(w) and the Kit(s) allele from Mus spretus. The Kit(w)/Kit(s) males showed hybrid sterility with small testes , but the females were fertile. The development of the seminiferous tubules of Kit(W)/Kit(s) males stopped before the spermatocyte stage and they were almost free of sperm. The Kit gene is located at position 42 on chromosome 5. We investigated in the C57BL-Kits congenic strain which part of the chr omosomal region adjacent to the Kits allele is introduced from SPR into a C 57BL background. The region between positions 42 and 44 was derived from SP R. Eleven amino acid substitutions of the Kit(s) cDNA were detected by comp arison with the sequence data of the +(Kit) cDNA from C57BL; seven were in the extracellular domain, one in the transmembrane domain, two in the kinas e I domain, and one in the carboxy-terminal tail. The Kit mRNA derived from both Kit(w) and Kit(s) alleles was expressed in the sterile testes of Kit( w)/Kit(s) males.