Genetic Analysis of the Enhancer of Zeste Locus and Its Role in Gene Regulation in Drosophila Melanogaster

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The Enhancer of zeste [E(z)] locus of Drosophila melanogaster is implicated in multiple examples of gene regulation during development. First identified as dominant gain-of-function modifiers of the zeste(1)-white (z-w) interaction, mutant E(z) alleles also produce homeotic transformations. Reduction of E(z)(+) activity leads to both suppression of the z-w interaction and ectopic expression of segment identity genes of the Antennapedia and bithorax gene complexes. This latter effect defines E(z) as a member of the Polycomb-group of genes. Analysis of E(z)(s2), a temperature-sensitive E(z) allele, reveals that both maternally and zygotically produced E(z)(+) activity is required to correctly regulate the segment identity genes during embryonic and imaginal development. As has been shown for other Polycomb-group genes, E(z)(+) is required not to initiate the pattern of these genes, but rather to maintain their repressed state. We propose that the E(z) loss-of-function eye color and homeotic phenotypes may both be due to gene derepression, and that the E(z)(+) product may be a general repressing factor required for both examples of negative gene regulation.

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