Polyhomeotic: A gene of Drosophila melanogaster required for correct expression of segmental identity

Abstract

A new locus in Drosophila melanogaster that is required for the correct expression of segmental identity has been discovered. The new locus, termed polyhomeotic (ph), is X-linked and maps cytologically to bands 2D2-3. Homozygous ph flies have homeotic transformations similar to those of known dominant gain of function mutants in the Antennapedia and bithorax complexes (ANT-C, BX-C), and in addition show loss of the humerus. ph interacts with three other similar mutations: Polycomb (Pc), Polycomblike (Pcl), and extra sex comb (esc), and acts as a dominant enhancer of Pc. The expression of ph depends on the ANT-C and BX-C dosage. ph has no embryonic phenotype, but temperature shift studies on ph2 show that the ph+ product is required during embryogenesis and larval development. We propose that ph mutants in some way disrupt the normal expression of the ANT-C and BX-C, and, therefore, that ph+ is needed for maintenance of segmental identity.

polyhomeoticis required for somatic cell proliferation and differentiation during ovarian follicle formation inDrosophila

“…This was substantiated by the fact that 4061/w; da-GAL4/+ females showed a partial homeotic haltere-to-wing transformation and abnormal expression of the vestigial QElacZ transgene in haltere imaginal discs (data not shown) (Kim et al, 1996;Weatherbee et al, 1998). Indeed, the opposite homeotic transformation, from wing to haltere, is obtained in flies carrying homozygous/hemizygous loss-of-function ph alleles, which corresponds to the phenotype associated with dominant gain-of-function mutations in genes of the Antennapedia and bithorax complexes (Dura et al, 1985).…”

polyhomeotic regulatory sequences induce developmental regulator-dependent variegation and targeted P-element insertions in Drosophila.

“…The maintenance of this specific pattern depends on two groups of transregulator genes: the trithorax group (trx-G) and the Polycomb group (Pc-G) (Lewis 1978;Struhl 1981;Duncan 1982;J~rgens 1985;Kennison and Tamkun 1988;for reviews, see Ingham 1985;Paro 1990;Kennison and Tamkun 1992), which maintain the active and inactive state, respectively, of homeotic gene transcription during the rest of development (Struhl and Akam 1985;Wedeen et al 1986;Dura and Ingham 1988;Huang and Dawid 1990;Jones and Gelbart 1990;Mazo et al 1990;McKeon and Brock 1991;Simon et al 1992;Tamkun et al 1992). The polyhomeotic (ph) locus h~s been defined as a member of the Pc-G because it exhibits the posteriorly homeotic transformations characteristic of Pc-G mutant phenotypes (Dura et al 1985(Dura et al , 1987. Members of the Pc-G act synergistically on homeotic gene transcription--double or triple mutant combinations showing more dramatic homeotic transformations than the simple addition of each mutant effect (J/irgens 1985).…”

The polyhomeotic gene of Drosophila encodes a chromatin protein that shares polytene chromosome-binding sites with Polycomb.

“…ph is genetically complex (Dura et al 1987), and ph mutants exhibit pleiotropic phenotypes (Dura et al 1985(Dura et al , 1987Smouse et al 1988;Santamaria et al 1989;Smouse and Perrimon 1990). Two genetic lesions are required on the same chromosome to create null or strong hypomorophic alleles, whereas weak hypomorphs result from any single-lesion alleles.…”