A MASSIVE NEW POSTTRANSLATIONAL MODIFICATION OCCURS ON AXONEMAL TUBULIN AT THE FINAL STEP OF SPERMATOGENESIS IN DROSOPHILA

Using two antibodies raised against Paramecium axonemal tubulin, a mon oclonal antibody, AXO 49 (Callen et al., Biol, Cell 81, 95-119 (1994)) , and a polyclonal antibody PAT (Cohen et al., Biol, Cell 44, 35-44 (1 982)), which have been shown elsewhere to detect a new posttranslation al modification of tubulin presumably corresponding to polyglycylation , we have analyzed the occurrence of this modification during spermato genesis in Drosophila. Results obtained by immunofluorescence on cysts isolated by laceration of testes showed that the antibodies reacted o n axonemal microtubules of several species within the genus, Observati on of different stages of differentiation of D. obscura sperm cells in dicated, first, that the epitopes reactive with both antibodies appear ed at late stages, and secondly, that they were detected simultaneousl y along all axonemes within a cyst, Immunofluorescence on semithin sec tions and electron microscopic immunocytochemistry on ultrathin sectio ns confirmed that the appearance of the epitope recognized by the mono clonal antibody occurred at the time of the individualization process of spermatids in D, melanogaster, These results indicate that the post translational modification occurs as a very late event, after complete assembly of axonemal microtubules, and that the axonemal tubulin beco mes modified when axonemal microtubules become coupled with the membra ne, suggesting that the modification may in some way be induced by the microtubule-membrane interaction.