Abnormal Spermiogenesis in Quaking, a Myelin-Deficient Mutant Mouse1

Quaking (qk), an autosomal recessive mutation previously reported to cause deficient myelination in the central nervous system, is now shown to cause virtual azoöspermia in homozygous male mice. Kinetic analysis of spermatogenesis indicates that the defect is one of spermatid differentiation, not of production. Electron microscopic examination of spermiogenesis in the mutant demonstrates two principal morphogenetic defects. (1) As chromatin condenses the nucleus and structures surrounding it assume abnormal shapes. Extensions of the adjacent Sertoli cell indent the nuclear space of the spermatid. (2) The axoneme of the flagellum becomes disorganized. Many normal features of spermatid ultrastructure, including some that have not previously been described in the mouse, e.g., the mortise and a substructure of the acrosome’s equatorial segment, differentiate normally in affected spermatids. The multiple effects of the qk mutation may be mediated by a single biochemical abnormality, perhaps of lipid metabolism, but the qk locus is near a complex region, T, known to carry other genes influencing sperm morphogenesis and motility; the possibility is raised that qk is interacting with neighboring loci and may exert its pleiotropic effects by more than one mechanism.