RESUMEN
The polyhomeotic (ph) gene of Drosophila melanogaster encodes a chromatin 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. Distribution of ph protein and mRNA coincided, except in early embryogogenesis. During blastoderm, ph mRNA is present in anterior and posterior domains that are themselves subdivided into stripes. During germ band extension, a segmentally repeated striped pattern of mRNA expression is seen. ph protein is first detected as a nuclear protein during cell cycle 10, and is ubiquitously expressed. ph protein stains more heavily in the ectodermal mitotic domains described by Foe (1989). Later, ph mRNA and protein expression is concentrated in the neuronal cell bodies of the central nervous system, and can also be detected in the peripheral nervous system. In imaginal discs, ph expression is non-uniform 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 nurse 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.
RESUMEN
Members of thePolycomb (Pc) group of genes are required for the correct determination of segment identity, and are thought to be negative regulators of thebithorax andAntennapedia complexes. This hypothesis has been tested molecularly for only some members of thePc group. Here, we examine the distribution ofUltrabithorax (Ubx),Antennapedia (Antp), andSex combs reduced (Scr) proteins in the epidermis, central nervous system, and midgut of embryos homozygous for mutations in tenPc group genes. We show that zygotic loss of mostPc group genes causes ectopic expression ofUbx andAntp, but that there are differences in time and tissue-specificity. FivePc group mutations lack midgut constrictions and also exhibit ectopic or suppressedUbx expression and suppression ofAntp expression. Distribution ofAntp is upset earlier than distribution ofUbx in the central nervous system of everyPc group mutant affecting both genes. Loss of the zygotic products ofPolycomb, extra sex combs, andAdditional sex combs cause ectopic expression ofScr in epidermis, and allPc group genes exceptPsc have suppressedScr expression in the nervous system. These results are discussed with respect to the function of thePc group.