Offspring from normal mouse oocytes injected with sperm heads from the azh/azh mouse display more severe sperm tail abnormalities than the original mutant

Sperm with abnormalities in the position and shape of the head were obtaine d from the azh/azh mutant and injected into the cytoplasm of mature mouse o ocytes to determine whether sperm from the offspring display both head (clu b shape) and tail (looping, folding, and fusion) abnormalities observed in the mutant donor. Although quantitative differences were observed among the three examined offspring, we found that abnormalities in sperm head shape were less frequent than in the donor mutant, but that tail malformations pr edominated. In addition, we found that the frequency of tail abnormalities increased during sperm epididymal transit. A typical defect was the multipl e folding of the sperm tail and eventual fusion of closely apposed plasma m embranes. As a consequence, sperm forward motility and natural fertility we re compromised. Results of this study indicate that the azh/azh mutant and offspring generated by intracytoplasmic sperm injection provide a valuable model for determining the role of the manchette and keratin-containing oute r dense fibers and fibrous sheath during spermiogenesis. Furthermore, our f indings stress the risk of enhancing a phenotypic abnormality caused by mut ant male genotypes introduced through bypassing the biologic mechanisms of natural sperm selection during fertilization.