Mutations in a Novel Locus on Mouse Chromosome 11 Resulting in Male Infertility Associated with Defects in Microtubule Assembly and Sperm Tail Function1

Traditional gene knock-out approaches using homologous re-combination in embryonic stem cells are routinely used to pro-vide functional information about genes involved in reproduc-tion. In the present study, we examined a novel approach using N-ethyl-N-nitrosourea (ENU) together with a balancer chro-mosome mating strategy to identify new loci with functional roles in male fertility. Our genetic strategy is a forward-genetic approach; thus, our phenotypic investigation begins with the discovery of an abnormal phenotype without previous knowl-edge of the mutant locus. We isolated eight recessive mutations on chromosome 11 that resulted in male or female infertility from a screen of 184 founder pedigrees from ENU-treated males. After testing the six male infertile and two female infertile mutations for their ability to complement, we found that three independent recessive male infertile mutations failed to comple-ment each other. The male infertility was associated with re-duced epididymal sperm count, a block in late-spermatid differ-entiation, and increased apoptosis. Furthermore, the three male infertile mutants had severe defects in epididymal sperm mor-phology associated with incorrect microtubule assembly. Elec-tron microscopy revealed unique defects in sperm head and tail morphology for each of the three alleles. One allele had an ab-normal manchette assembly of the sperm head. The other two alleles had different abnormalities in the 912 patterning of the microtubules in the sperm tail axoneme, with one containing only five of the microtubule doublets and the other containing an extra doublet. The isolation of this allelic series identifies a new locus on mouse chromosome 11 that is required for sper-miogenesis and male fertility. male reproductive tract, sperm, sperm maturation, sperm motility and transport, testi