COMPARISON OF GERMLINE MOSAICS OF GENES IN THE POLYCOMB GROUP OF DROSOPHILA-MELANOGASTER

The genes of the Polycomb group (PcG) repress the genes of the bithora x and Antennapedia complexes, among others. To observe a null phenotyp e for a PcG gene, one must remove its maternal as well as zygotic cont ribution to the embryo. Five members of the PcG group are compared her e: Enhancer of Polycomb [E(Pc)], Additional sex combs (Asx), Posterior sex combs (Psc), Suppressor of zeste 2 [Su(z)2] and Polycomblike (Pcl ). The yeast recombinase (FLP) system was used to induce mitotic recom bination in the maternal germline. Mutant embryos were analyzed by sta ining with antibodies against six target genes of the PcG. The loss of the maternal component leads to enhanced homeotic phenotypes and to u nique patterns of misexpression. E(Pc) and Su(z)2 mutations had only s ubtle effects on the target genes, even when the maternal contribution s were removed. Asx and Pcl mutants show derepression of the targets o nly in specific cell types. Pse shows unusual effects on two of the ta rgets, Ultrabithorax and abdominal-A. These results show that the PcG genes do not act only in a common complex or pathway; they must have s ome independent functions.