Range of potential functions of the Drosophila melanogaster hdc gene

The Drosophila melanogaster hdc gene controls trachea branching, which starts during embryo development. Expression in imaginal disks and reproductive organs suggests additional functions for the hdc gene. The gene was demonstrated to have a maternal effect, which was denied previously. Analysis of cell proliferation in imaginal disks with hdc mutations showed that the gene does not possess tumor suppressor properties at the levels of mosaic cuticle clones of adults and transplanted imaginal disks. Transplanted imaginal disks homozygous, but not heterozygous, for an hdc mutation were found to affect oogenesis in the recipient females, implicating the hdc activity in exchanging signals between different organs. Amino acid sequence analysis of the Hdc protein revealed a region homologous to the human HRS proteins, which directly interact with the NF2 tumor suppressor on experimental evidence.     

The Levels of the bancal Product, a Drosophila Homologue of Vertebrate hnRNP K Protein, Affect Cell Proliferation and Apoptosis in Imaginal Disc Cells

We have characterized the Drosophila bancal gene, which encodes a Drosophila homologue of the vertebrate hnRNP K protein. The bancal gene is essential for the correct size of adult appendages. Reduction of appendage size in bancal mutant flies appears to be due mainly to a reduction in the number of cell divisions in the imaginal discs. Transgenes expressing Drosophila or human hnRNP K are able to rescue weak bancal phenotype, showing the functional similarity of these proteins in vivo. High levels of either human or Drosophila hnRNP K protein in imaginal discs induces programmed cell death. Expression of the antiapoptotic P35 protein suppresses this phenotype in the eye, suggesting that apoptosis is the major cellular defect caused by overexpression of K protein. Finally, the human K protein acts as a negative regulator of bancal gene expression. We propose that negative autoregulation limits the level of Bancal protein produced in vivo.     

Expanded functions in the apical cell domain to regulate the growth rate of imaginal discs

The Drosophila expanded (ex) gene encodes a product (Ex) that shares homology with the Protein 4.1 family of proteins, many of which are enriched at specific lateral cell junctions and the apical cellular domain. Ex colocalizes with actin in the apical domain of imaginal disc epithelial cells, where it partially overlaps the distribution of phosphotyrosine (PY)-containing proteins. This suggests that Ex is present in or associated with adherens junctions. Genetic studies show that Ex is necessary for proper regulation of final cell number in adult wings and for the formation of eyes, distal leg, and distal antennal segments. We have generated mitotic clones that lack Ex using the twin spot technique, and demonstrated that the primary function of Ex is to regulate cell proliferation. Overexpressing Ex protein results in a decrease in final cell number in wings, suggesting a direct relationship between Ex function and proliferation rate. Dev. Genet. 20:103–110, 1997. © 1997 Wiley-Liss, Inc.     

Ecdysteroid action in imaginal discs of Drosophila melanogaster does not involve cyclic AMP

A possible role for cAMP in the mechanism of ecdysteroid induction of morphogenesis in imaginal discs of Drosophila melanogaster was explored in a variety of experiments. Neither cAMP, supplied externally, nor theophylline at concentrations which increase internal cAMP levels 2–3 fold will substitute for the hormone in the induction of morphogenesis. Hormone action in imaginal discs is neither enhanced nor repressed by externally supplied cAMP or theophylline. Internal cAMP levels in discs, determined by kinase binding assays, are not altered by juvenile hormone or 20-hydroxy-ecdysone under incubation conditions which permit ecdysteroid stimulation of RNA synthesis and induction of morphogenesis. Adenylate cyclase activity in disc extracts is not stimulated or depressed by 20-hydroxy-ecdysone or juvenile hormone, but is stimulated by NaF. These findings suggest that ecdysteroid action in imaginal discs does not involve changes in the internal concentration or metabolism of cAMP.