Temperature-sensitive mutations in Drosophila melanogaster: XI. Male sterile mutants of the Y chromosome

Abstract

Eight temperature-sensitive ( ts) male sterile mutations have been induced by ethyl methanesulfonate treatment of Y chromosomes derived from a selected temperature-resistant Amherst wild-type stock of Drosophila melanogaster. Males carrying such mutated Y chromosomes (Y ts ) are sterile when raised at 29°C but fertile when reared at 22°C. Complementation tests of the mutants with Y chromosome fragments, deletions, and inter se localized all eight to the long arm of the chromosome in four different complementation groups. When Y ts -bearing males, reared to adulthood at 22°C, were subjected to a 48-hr regimen at 29°C and mated to fresh virgin females daily, a significant reduction in fertility resulted 5 days after initiation of 29°C treatments. This period of sterility was transient (48–72-hr duration) and corresponded to a temperature-sensitive period (TSP) of spermatogenesis during the primary spermatocyte stage. A more precise definition of the TSP utilized exposure of subadult males to 29°C at selected developmental periods during which only certain germ cell stages are present. Upon eclosion adult males were subjected to a similar schedule of consecutive matings of 12-hr duration in order to detect any delay in the appearance of fertility. Different ts males could be distinguished by the resultant pattern of sterility, and the TSP of different mutations thus localized to either primary spermatocyte or immediately post-meiotic stage. Associated with Y ts -mediated sterility, spermiogenesis is defective at restrictive temperature as evidenced by the production of nonmotile sperm and a failure to transfer such sperm to the female during copulation. In addition, electron microscopy detected a variety of ultrastructural abnormalities, including defects of axoneme formation, irregularities of Nebenkern derivative development, and failures of separation from the syncitial state or mature cyst with subsequent degeneration.