Spermiogenesis and Spermatozoa in Sterile Mice Carrying Different Lethal T/t Locus Haplotypes: A Transmission and Scanning Electron Microscopic Study

Abstract

Spermiogenesis and the morphology of spermatozoa in sterile mice carrying 2 different lethal t-haplotypes (T/t-locus) has been studied by transmission and scanning electron microscopy. In mice heterozygous for the haplotype t⁰ and t^w32 (genotype t⁰/t^w32) nuclei of late spermatids fail to elongate normally. Also, derrangements of the microtubules produce abnormal indentations of the nucleus. Likewise acrosomes develop irregularities of shape which persist in spermatozoa. Spermatozoa acquire additional abnormalities while they mature in the excurrent ducts. Acrosomes frequently show extensive areas of separation from the nuclear membrane. In thin sections, about 10 percent of spermatozoa from the vas deferens exhibit missing or misplaced microtubules within the axoneme, defects that are absent in testicular and caput epididymal spermatozoa. By SEM 60-75 percent of spermatozoa show abnormally short, angular or amorphous heads. The irregularities of the shape of the acrosome can frequently be clearly viewed as well as prominent bulges and ridges, probably reflecting areas of dehiscence of acrosome from the nucleus. Defective chromosomal condensation may explain the abnormality of nuclear elongation. Membrane defects may be responsible for the disorganized microtubules of the manchette and for the failure of the acrosome to maintain a normal attachment to the nucleus.