Sperm abnormalities in the PL/J mouse strain: A description and proposed mechanism for malformation

A high frequency (42%) of sperm from the inbred homozygous mouse strain PL/J are abnormal. Head shape abnormalities occur in 15% of the total sperm; and 27% of the sperm are headless, with the mitochondria condensed into a mass at the caudal end of the midpiece region. The sperm without heads exhibit relatively normal motility. Electron microscopy of the testes indicates that some of the abnormal sperm in PL/J males result from a failure of the paired centrioles to attain a normal position on the nucleus opposite the acrosome prior to implantation, or to attach at all. The centrioles that are not attached to the nuclear envelope can differentiate to form the principal piece and midpiece region. The frequency of headless variants in heterozygous F₁ indicates that the trait is mainly recessive. The offspring from the backcross of the F₁ to homozygous PL/J parents did not give a clear-cut segregation pattern. The frequency of abnormal sperm in the F₁ and the backcross is higher when the female parent is a PL/J.