[Molecular and genetic description of a new hypomorphic mutation of Trithorax-like gene and analysis of its effect on Drosophila melanogaster oogenesis].

The Trithorax-like (Trl) gene of Drosophila melanogaster encodes the multifunctional protein GAGA involved in many cellular processes. We have isolated and described a new hypomorphic mutation of the Trl gene--Trl(en82). The mutation is the insertion of a 1.4 kb P-element into the 5' untranslated region. Trl expression decreased in the ovaries of mutant flies by about 30%; however, it caused abnormalities. The Trl(en82) mutation combined with the null allele of Trl caused female sterility: the females laid a few small eggs with abnormal shape. Many egg chambers demonstrated abnormalities in the Trl(en82) mutants: the oocyte had a regular shape and intruded into the egg chamber region with nurse cells; the rapid transport of nurse cell cytoplasm into the oocyte was disturbed, which resulted in the "dumpless" phenotype of the chambers in mutants; follicular cells often did not completely cover the oocyte and concentrated on its posterior end; and the migration of centripetal cells was affected. We propose that the sterility of the Trl(en82) females is due to the abnormal functioning of follicular cells resulting from low Trl expression. This proposal is confirmed by normalizing the mutant phenotype of Trl(en82) females after the transfection of Trl cDNA. Note that even an insignificant decrease in Trl expression in such females seriously affected the somatic cell functioning, while a significant decrease in its expression in strong hypomorphic mutants affected both somatic and germline cells in the egg chambers.