Occurrence of Small, Round Vesicles in the Acrosome of Elongating Spermatids from a Mouse Mutant Line with Partial Deletion of the Y Chromosome

To elucidate abnormality of acrosome formation in germ cells of the B10.BR-Ydel (Ydel) mutant mouse, male mouse lines were produced by crossing the Ydel males with females from a transgenic mouse line, Acr-EGFP, carrying a transgene encoding a fusion protein of mouse pre-proacrosin and jellyfish enhanced green fluorescence protein (EGFP) under the control of the promoter of the mouse acrosin gene. Morphological analysis indicated that green fluorescence due to EGFP was non-uniformly localized in the acrosomal cap regions of cauda epididymal sperm in Ydel/Acr-EGFP mouse sperm. When spermatogenic cells at twelve stages of the seminiferous epithelial cycle were examined, no significant difference of the acrosome formation was observed between the wild-type and Ydel/Acr-EGFP mice, except that small, round vesicles without green fluorescence were frequently found in the acrosome of elongating spermatids at stage IX and later stages only in the mutant mouse. Some fluorescence-less vesicles were eliminated from the acrosome of elongating spermatids during late spermiogenesis. However, most of the fluorescence-less vesicles were retained in the acrosome. These results suggest that the occurrence of the small, round vesicles within the acrosome may correlate with the production of abnormal sperm with flat heads in the Ydel mutant mouse.