EXPRESSION OF THE POLYHOMEOTIC LOCUS IN DEVELOPMENT OF DROSOPHILA-MELANOGASTER

The polyhomeotic (ph) gene of Drosophila melanogaster encodes a chroma tin protein required for negative regulation of homeotic genes, and is a member of the Polycomb group of genes. The distribution of ph mRNA and protein was determined in embryos, imaginal discs, and ovaries. Di stribution of ph protein and mRNA coincided, except in early embryogog enesis. During blastoderm, ph mRNA is present in anterior and posterio r domains that are themselves subdivided into stripes. During germ ban d extension, a segmentally repeated striped pattern of mRNA expression is seen. ph protein is first detected as a nuclear protein during cel l cycle 10, and is ubiquitously expressed. ph protein stains more heav ily in the ectodermal mitotic domains de scribed by Foe (1989). Later, ph mRNA and protein expression is concentrated in the neuronal cell b odies of the central nervous system, and can also be detected in the p eripheral nervous system. In imaginal discs, ph expression is non-unif orm in metathoracic discs, but appears more regular in other imaginal discs. The ph mRNA is found in the germarium and in stages 1-10 in nur se cells and follicle cells, but we do not detect it in oocytes. These results are discussed with respect to the expression of Polycomb, and with respect to the function of the Polycomb group.