MUTATIONS IN SOME POLYCOMB GROUP GENES OF DROSOPHILA INTERFERE WITH REGULATION OF SEGMENTATION GENES

Mutations in several Polycomb (Pc) group genes cause maternal-effect o r zygotic segmentation defects, suggesting that Pc group genes may reg ulate the segmentation genes of Drosophila. We show that individuals d oubly heterozygous for mutations in polyhomeotic and six other Pc grou p genes show gap, pair rule, and segment polarity segmentation defects . We examined double heterozygous combinations of Pc group and segment ation mutations for enhancement of adult and embryonic segmentation de fects. Posterior sex combs and polyhomeotic interact with Kruppel(2) a nd enhance embryonic phenotypes of hunchback and knirps, and polyhomeo tic enhances even-skipped. Surprisingly, flies carrying duplications o f extra sex combs (esc), that were heterozygous for mutations of even- skipped (eve), were extremely subvital. Embryos and surviving adults o f this genotype showed strong segmentation defects in even-numbered se gments. Antibody studies confirm that expression of eve is suppressed by duplications of esc. However, esc duplications have no effect on ot her gap or pair rule genes tested. To our knowledge, this is only the second triplo-abnormal phenotype associated with Pc group genes. Dupli cations of nine other Pc group genes have no detectable effect on eve. Expression of engrailed (en) was abnormal in the central nervous syst ems of most Pc group mutants. These results support a role for Pc gene s in regulation of some segmentation genes, and suggest that esc may a ct differently from other Pc group genes.