ABSTRACT
The Drosophila Homothorax (HTH) and Extradenticle (EXD) are two homeoproteins required in a number of developmental processes. EXD can function as a cofactor to Hox proteins. Its nuclear localization is dependent on HTH. In this study we present evidence of in vivo physical interaction between HTH and EXD, mediated primarily through an evolutionarily conserved MH domain in HTH. This interaction is essential for the mutual stabilization of both proteins, for EXD nuclear localization, and for the cooperative DNA binding of the EXD-HTH heterodimer. Some in vivo functions require both EXD and HTH in the nucleus, suggesting that the EXD-HTH complex may function as a transcriptional regulator.
Subject(s)
Drosophila Proteins , Homeodomain Proteins/metabolism , Transcription Factors/metabolism , Amino Acid Sequence , Animals , Binding Sites , Cell Nucleus/metabolism , Conserved Sequence , DNA/metabolism , Drosophila/genetics , Drosophila/metabolism , Drosophila/physiology , Homeodomain Proteins/genetics , Homeodomain Proteins/physiology , Humans , Mice , Molecular Sequence Data , Transcription Factors/genetics , Transcription Factors/physiologyABSTRACT
The Extradenticle (Exd) protein in Drosophila acts as a cofactor to homeotic proteins. Its nuclear localization is regulated. We report the cloning of the Drosophila homothorax (hth) gene, a homolog of the mouse Meis1 proto-oncogene that has a homeobox related to that of exd. Comparison with Meis1 finds two regions of high homology: a novel MH domain and the homeodomain. In imaginal discs, hth expression coincides with nuclear Exd. hth and exd also have virtually identical, mutant clonal phenotypes in adults. These results suggest that hth and exd function in the same pathway. We show that hth acts upstream of exd and is required and sufficient for Exd protein nuclear localization. We also show that hth and exd are both negative regulators of eye development; their mutant clones caused ectopic eye formation. Targeted expression of hth, but not of exd, in the eye disc abolished eye development completely. We suggest that hth acts with exd to delimit the eye field and prevent inappropriate eye development.
Subject(s)
DNA-Binding Proteins/physiology , Drosophila Proteins , Drosophila/growth & development , Eye/growth & development , Homeodomain Proteins/genetics , Homeodomain Proteins/physiology , Transcription Factors/physiology , Amino Acid Sequence , Animals , Cell Nucleus/chemistry , Cloning, Molecular , DNA-Binding Proteins/analysis , DNA-Binding Proteins/genetics , Drosophila/chemistry , Drosophila/genetics , Gene Expression/genetics , Gene Expression/physiology , Gene Expression Regulation, Developmental , Genes, Insect/genetics , Homeodomain Proteins/analysis , Molecular Sequence Data , Mutation/genetics , Myeloid Ecotropic Viral Integration Site 1 Protein , Neoplasm Proteins/genetics , Phenotype , Sequence Alignment , Sequence Homology, Amino Acid , Tissue Distribution , Transcription Factors/analysis , Transcription Factors/geneticsABSTRACT
The white+ gene was used as a reporter to detect transcriptional silencer activity in the Drosophila genome. Changes in the spatial expression pattern of white were scored in the adult eye as nonuniform patterns of pigmentation. Thirty-six independent P[lacW] transposant lines were collected. These represent 12 distinct pigmentation patterns and probably 21 loci. The spatial pigmentation pattern is due to cis-acting suppression of white+ expression, and the suppression probably depends on cell position rather than cell type. The mechanism of suppression differs from inactivation by heterochromatin. In addition, activation of lacZ in P[lacW] occurs also in specific patterns in imaginal discs and embryos in many of the lines. The expression patterns of white+ and lacZ may reflect the activity of regulatory elements belonging to an endogenous gene near each P[lacW] insertion site. We speculate that these putative POSE (position-specific expression) genes may have a role in pattern formation of the eye as well as other imaginal structures. Three of the loci identified are optomotor-blind, engrailed and invected. teashirt is also implicated as a candidate gene. We propose that this "silencer trap"' may be an efficient way of identifying genes involved in imaginal pattern formation.