Gametogenesis is normal through meiosis and the earliest phases of spermiogenesis in male-sterile mice homozygous for the recessive, pleiotropic, mutationhpy(hydrocephalic-polydactyl). However, structurally complete sperm flagella were not encountered. Instead, partially assembled axonemal structures and/or poorly organized aggregates of other tail components (mitochondria, outer coarse fibers) were seen at the posterior poles of nuclei in older spermatids. The ultrastructure of centrioles in spermatids was normal, but that of axonemes associated with them was not. These findings suggest that the observed flagella dysgenesis results from defects in assembly rather than from defective intiation centers. Released “gametes” usually consisted of distorted nuclei and associated acrosome enclosed in a relatively close fitting plasma membrane. Perturbations of sperm head development were also encountered; they included extreme nuclear elongation, and distortion of the acrosome and underlying nuclear material by inpushings of finger-like processes of Sertoli cells. It is believed that sperm head anomalies are secondary consequences of the mutant condition. The findings support the view that thehpylocus represents one of a number of genes primarily involved in the mediation of flagella developm
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