Inadequate function of sterile tw5/tw32 spermatozoa overcome by intracytoplasmic sperm injection

Mice carrying two t complementary haplotypes (tw5/tw32) are totally sterile. Their spermatozoa have poor motility and fertilize neither zone‐intact nor zona‐free oocytes, even though they are structurally indistinguishable from control (wild‐type) spermatozoa. However, when injected directly into oocytes, these infertile spermatozoa are able to participate in normal development. This suggests that infertility of tw5/tw32 male (spermatozoa) is more likely to be due to poor sperm‐oocyte interaction than to genetic incompetence of sperm nuclei. © 1996 Wiley‐Liss, Inc.