Failure of acrosome assembly in a male sterile mouse mutant

Blind-sterile (bs) is a new autosomal recessive mutation of the mouse that causes sterility in males and bilenticular cataracts in both sexes. Sterile bs/bs males exhibited normal copulatory behavior, reduced testis weights, and few or no epididymal sperm. The effects of the bs mutation on spermatogenesis were examined by light and electron microscopy. All sperm present were morphologically abnormal with aberrant head shape. Adult bs/bs testes were characterized by germ cell depletion that resulted in profound alterations of the typical germ cell associations. Only 30% of the tubules contained relatively normal germ cell associations while 39% were extensively depleted, showing only Sertoli cells or Sertoli cells and spermatogonia. The most striking effect of the bs mutation on spermiogenesis was the failure of acrosome formation. Disorganized proacrosomic granules were detected up to step 3 of spermiogenesis by both periodic acid-Schiff staining and ultrastructural analysis. In over 3500 spermatids scored past steps 3-4 of spermiogenesis not a single acrosomal cap or fully developed acrosome was detected. Electron microscopy revealed a thickening of the nuclear envelope of elongating spermatids in the region where the acrosome should have been located; however, no acrosome was present. Chromatin condensation and nuclear elongation did occur in these acrosomeless spermatids, suggesting that caudal growth of the acrosome is not a mechanistic factor in these events.