The testis-specific beta-tubulin subunit in Drosophila melanogaster has multiple functions in spermatogenesis.

We have isolated four recessive male sterile mutations in the structural gene for the testis-specific Drosophila beta 2-tubulin. Each of these mutations encodes a variant beta 2-tubulin subunit synthesized at normal levels, but which is subsequently unstable and rapidly degraded within the testis. In such testes, the normal alpha tubulins are also synthesized at normal levels and then degraded. Thus in mutant males the testis tubulin pool is drastically reduced relative to wild-type. In males homozygous for any of the recessive beta 2-tubulin mutations, the early mitotic divisions, which are completed before the time of synthesis of beta 2-tubulin, are normal. Thereafter, however, all microtubule-mediated events subsequent to the expression of the altered subunit are defective: meiosis, nuclear shaping and assembly of the axoneme all fail to occur. We thus conclude that the beta 2-tubulin subunit that forms the Drosophila sperm axoneme is not functionally restricted but serves multiple functions in spermatogenesis, including the assembly of both singlet and doublet tubules.