ABSTRACT
The patterning function of Hox proteins relies on assembling protein complexes with PBC proteins, which often involves a protein motif found in most Hox proteins, the so-called Hexapeptide (HX). Hox/PBC complexes likely gained functional diversity by acquiring additional modes of interaction. Here, we structurally characterize the first HX alternative interaction mode based on the paralogue-specific UbdA motif and further functionally validate structure-based predictions. The UbdA motif folds as a flexible extension of the homeodomain recognition helix and defines Hox/PBC contacts that occur, compared with those mediated by the HX motif, on the opposing side of the DNA double helix. This provides a new molecular facet to Hox/PBC complex assembly and suggests possible mechanisms for the diversification of Hox protein function.
Subject(s)
DNA/metabolism , Drosophila Proteins/chemistry , Drosophila Proteins/metabolism , Drosophila/chemistry , Homeodomain Proteins/chemistry , Homeodomain Proteins/metabolism , Macromolecular Substances/metabolism , Models, Molecular , Transcription Factors/chemistry , Transcription Factors/metabolism , Amino Acid Sequence , Animals , Crystallization , Electrophoretic Mobility Shift Assay , Molecular Probes/genetics , Molecular Sequence Data , Protein Folding , Protein Structure, TertiaryABSTRACT
BACKGROUND: Hox genes encode transcription factors playing important role in segment specific morphogenesis along the anterior posterior axis. Most work in the Hox field aimed at understanding the basis for specialised Hox functions, while little attention was given to Hox common function. In Drosophila, genes of the Bithorax complex [Ultrabithorax (Ubx), abdominalA (abdA), and AbdominalB (AbdB)] all promote abdominal identity. While Ubx and AbdA share extensive sequence conservation, AbdB is highly divergent, questioning how it can perform similar functions as Ubx and AbdA. RESULTS: In this study, we investigate the genetic requirement for the specification of abdominal-type denticles by Ubx, AbdA, and AbdB. The impact of ectopic expression of Hox proteins in embryos mutant for Exd as well as of Wingless or Hedgehog signaling involved in intrasegmental patterning was analyzed. Results indicated that Ubx and AbdA do not require Exd, Wg, and Hh activity for specifying abdominal-type denticles, while AbdB does. CONCLUSIONS: Our results support that distinct regulatory mechanisms underlie Ubx/AbdA- and AbdB-mediated specification of abdominal-type denticles, highlighting distinct strategies for achieving a similar biological output. This suggests that common function performed by distinct paralogue Hox proteins may also rely on newly acquired property, instead of conserved/ancestral properties.
Subject(s)
Drosophila Proteins/metabolism , Embryo, Nonmammalian/metabolism , Animals , Drosophila/enzymology , Drosophila/genetics , Drosophila Proteins/genetics , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Transcription Factors/genetics , Transcription Factors/metabolismABSTRACT
The adult thorax of Drosophila melanogaster is covered by a stereotyped pattern of mechanosensory bristles called macrochaetes. Here, we report that the MYST containing protein Chameau (Chm) contributes to the establishment of this pattern in the most dorsal part of the thorax. Chm mutant pupae present extra-dorsocentral (DC) and scutellar (SC) macrochaetes, but a normal number of the other macrochaetes. We provide evidences that chm restricts the singling out of sensory organ precursors from proneural clusters and genetically interacts with transcriptional regulators involved in the regulation of achaete and scute in the DC and SC proneural cluster. This function of chm likely relies on chromatin structure regulation since a protein with a mutation in the conserved catalytic site fails to rescue the formation of supernumerary DC and SC bristles in chm mutant flies. This is further supported by the finding that mutations in genes encoding chromatin modifiers and remodeling factors, including Polycomb group (PcG) and Trithorax group (TrxG) members, dominantly modulate the penetrance of chm extra bristle phenotype. These data support a critical role for chromatin structure modulation in the establishment of the stereotyped sensory bristle pattern in the fly thorax.
Subject(s)
Acetyltransferases/metabolism , Drosophila Proteins/metabolism , Drosophila melanogaster/embryology , Drosophila melanogaster/genetics , Morphogenesis/genetics , Sense Organs/embryology , Acetyltransferases/genetics , Animals , Drosophila Proteins/genetics , Drosophila melanogaster/metabolism , Epistasis, Genetic , Gene Expression Regulation, Developmental , Genotype , Mutation , Organ Specificity/genetics , Phenotype , Sense Organs/metabolism , Thorax/embryology , Transcription Factors/geneticsABSTRACT
Protein function is encoded within protein sequence and protein domains. However, how protein domains cooperate within a protein to modulate overall activity and how this impacts functional diversification at the molecular and organism levels remains largely unaddressed. Focusing on three domains of the central class Drosophila Hox transcription factor AbdominalA (AbdA), we used combinatorial domain mutations and most known AbdA developmental functions as biological readouts to investigate how protein domains collectively shape protein activity. The results uncover redundancy, interactivity, and multifunctionality of protein domains as salient features underlying overall AbdA protein activity, providing means to apprehend functional diversity and accounting for the robustness of Hox-controlled developmental programs. Importantly, the results highlight context-dependency in protein domain usage and interaction, allowing major modifications in domains to be tolerated without general functional loss. The non-pleoitropic effect of domain mutation suggests that protein modification may contribute more broadly to molecular changes underlying morphological diversification during evolution, so far thought to rely largely on modification in gene cis-regulatory sequences.
Subject(s)
Body Patterning/genetics , Central Nervous System/embryology , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila melanogaster/genetics , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , Animals , Cell Lineage/genetics , Central Nervous System/growth & development , DNA-Binding Proteins/genetics , Drosophila Proteins/chemistry , Drosophila melanogaster/embryology , Drosophila melanogaster/growth & development , Gene Expression Regulation, Developmental , Genetic Association Studies , Mutation , Nuclear Proteins/chemistry , Protein Structure, Tertiary/genetics , Transcription Factors/chemistry , Wnt1 Protein/genetics , Wnt1 Protein/metabolismABSTRACT
Hox genes encode transcription factors widely used for diversifying animal body plans in development and evolution. To achieve functional specificity, Hox proteins associate with PBC class proteins, Pre-B cell leukemia homeobox (Pbx) in vertebrates, and Extradenticle (Exd) in Drosophila, and were thought to use a unique hexapeptide-dependent generic mode of interaction. Recent findings, however, revealed the existence of an alternative, UbdA-dependent paralog-specific interaction mode providing diversity in Hox-PBC interactions. In this study, we investigated the basis for the selection of one of these two Hox-PBC interaction modes. Using naturally occurring variations and mutations in the Drosophila Ultrabithorax protein, we found that the linker region, a short domain separating the hexapeptide from the homeodomain, promotes an interaction mediated by the UbdA domain in a context-dependent manner. While using a UbdA-dependent interaction for the repression of the limb-promoting gene Distalless, interaction with Exd during segment-identity specification still relies on the hexapeptide motif. We further show that distinctly assembled Hox-PBC complexes display subtle but distinct repressive activities. These findings identify Hox-PBC interaction as a template for subtle regulation of Hox protein activity that may have played a major role in the diversification of Hox protein function in development and evolution.
Subject(s)
Drosophila Proteins/metabolism , Evolution, Molecular , Homeodomain Proteins/metabolism , Transcription Factors/metabolism , Amino Acid Motifs , Animals , Drosophila Proteins/genetics , Drosophila melanogaster , Homeodomain Proteins/genetics , Protein Structure, Tertiary , Transcription Factors/geneticsABSTRACT
Deciphering the molecular bases of animal body plan construction is a central question in developmental and evolutionary biology. Genome analyses of a number of metazoans indicate that widely conserved regulatory molecules underlie the amazing diversity of animal body plans, suggesting that these molecules are reiteratively used for multiple purposes. Hox proteins constitute a good example of such molecules and provide the framework to address the mechanisms underlying transcriptional specificity and diversity in development and evolution. Here we examine the current knowledge of the molecular bases of Hox-mediated transcriptional control, focusing on how this control is encoded within protein sequences and structures. The survey suggests that the homeodomain is part of an extended multifunctional unit coordinating DNA binding and activity regulation and highlights the need for further advances in our understanding of Hox protein activity.
Subject(s)
Genes, Homeobox , Homeodomain Proteins , Amino Acid Motifs , Animals , Body Patterning/genetics , DNA/metabolism , Gene Expression Regulation , Genome , Homeodomain Proteins/chemistry , Homeodomain Proteins/classification , Homeodomain Proteins/physiology , Models, Molecular , Nucleic Acid Conformation , Phylogeny , Protein Binding , Protein ConformationABSTRACT
Organogenesis proceeds in multiple steps and events that need to be coordinated in time and space. Yet the genetic and molecular control of such coordination remains poorly understood. In this study we have investigated the contribution of three signalling pathways, Wnt/Wingless (Wg), Hedgehog (Hh), and epidermal growth factor receptor (EGFR), to posterior spiracle morphogenesis, an organ that forms under Abdominal-B (AbdB) control in the eighth abdominal segment. Using targeted signalling inactivation, we show that these pathways are reiteratively used to control multiple cellular events during posterior spiracle organogenesis, including cell survival and maintenance of cell polarity and adhesion required for tissue integrity. We propose that the reiterative use of the Wg, Hh, and EGFR signalling pathways serves to coordinate in time and space the sequential deployment of events that collectively allow proper organogenesis.
Subject(s)
Drosophila/embryology , Embryo, Nonmammalian/metabolism , Signal Transduction , Animals , Body Patterning , Drosophila/metabolism , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , ErbB Receptors/genetics , ErbB Receptors/metabolism , Hedgehog Proteins/genetics , Hedgehog Proteins/metabolism , Organogenesis , Wnt Proteins/genetics , Wnt Proteins/metabolismABSTRACT
Ectopic repression of retinoic acid (RA) receptor target genes by PML/RARA and PLZF/RARA fusion proteins through aberrant recruitment of nuclear corepressor complexes drives cellular transformation and acute promyelocytic leukemia (APL) development. In the case of PML/RARA, this repression can be reversed through treatment with all-trans RA (ATRA), leading to leukemic remission. However, PLZF/RARA ectopic repression is insensitive to ATRA, resulting in persistence of the leukemic diseased state after treatment, a phenomenon that is still poorly understood. Here we show that, like PML/RARA, PLZF/RARA expression leads to recruitment of the Polycomb-repressive complex 2 (PRC2) Polycomb group (PcG) complex to RA response elements. However, unlike PML/RARA, PLZF/RARA directly interacts with the PcG protein Bmi-1 and forms a stable component of the PRC1 PcG complex, resulting in PLZF/RARA-dependent ectopic recruitment of PRC1 to RA response elements. Upon treatment with ATRA, ectopic recruitment of PRC2 by either PML/RARA or PLZF/RARA is lost, whereas PRC1 recruited by PLZF/RARA remains, resulting in persistent RA-insensitive gene repression. We further show that Bmi-1 is essential for the PLZF/RARA cellular transformation property and implicates a central role for PRC1 in PLZF/RARA-mediated myeloid leukemic development.
Subject(s)
Cell Transformation, Neoplastic , Leukemia/physiopathology , Oncogene Proteins, Fusion/metabolism , Repressor Proteins/metabolism , Antineoplastic Agents/pharmacology , Chromatin/metabolism , Humans , Nuclear Proteins/metabolism , Polycomb Repressive Complex 1 , Polycomb-Group Proteins , Protein Binding/drug effects , Protein Structure, Tertiary , Proto-Oncogene Proteins/metabolism , Tretinoin/pharmacology , U937 CellsABSTRACT
Pontin (Pont) and Reptin (Rept) are paralogous ATPases that are evolutionarily conserved from yeast to human. They are recruited in multiprotein complexes that function in various aspects of DNA metabolism. They are essential for viability and have antagonistic roles in tissue growth, cell signalling and regulation of the tumour metastasis suppressor gene, KAI1, indicating that the balance of Pont and Rept regulates epigenetic programmes critical for development and cancer progression. Here, we describe Pont and Rept as antagonistic mediators of Drosophila Hox gene transcription, functioning with Polycomb group (PcG) and Trithorax group proteins to maintain correct patterns of expression. We show that Rept is a component of the PRC1 PcG complex, whereas Pont purifies with the Brahma complex. Furthermore, the enzymatic functions of Rept and Pont are indispensable for maintaining Hox gene expression states, highlighting the importance of these two antagonistic factors in transcriptional output.
Subject(s)
Carrier Proteins/metabolism , Chromosomal Proteins, Non-Histone/metabolism , DNA Helicases/metabolism , Drosophila Proteins/metabolism , Drosophila melanogaster/genetics , Gene Expression Regulation , Homeodomain Proteins/genetics , Repressor Proteins/metabolism , Animals , Cell Cycle Proteins/isolation & purification , Cell Cycle Proteins/metabolism , DNA Helicases/isolation & purification , Drosophila Proteins/isolation & purification , Drosophila melanogaster/cytology , Gene Silencing , Mutation/genetics , Polycomb-Group Proteins , Protein Binding , Trans-Activators/isolation & purification , Trans-Activators/metabolismABSTRACT
Hox transcription factors are essential for shaping body morphology in development and evolution. The control of Hox protein activity in part arises from interaction with the PBC class of partners, pre-B cell transcription factor (Pbx) proteins in vertebrates and Extradenticle (Exd) in Drosophila. Characterized interactions occur through a single mode, involving a short hexapeptide motif in the Hox protein. This apparent uniqueness in Hox-PBC interaction provides little mechanistic insight in how the same cofactors endow Hox proteins with specific and diverse activities. Here, we identify in the Drosophila Ultrabithorax (Ubx) protein a short motif responsible for an alternative mode of Exd recruitment. Together with previous reports, this finding highlights that the Hox protein Ubx has multiple ways to interact with the Exd cofactor and suggests that flexibility in Hox-PBC contacts contributes to specify and diversify Hox protein function.
Subject(s)
Drosophila Proteins/metabolism , Drosophila melanogaster/metabolism , Homeodomain Proteins/metabolism , Transcription Factors/metabolism , Amino Acid Motifs , Amino Acid Sequence , Animals , Antennapedia Homeodomain Protein/chemistry , Antennapedia Homeodomain Protein/metabolism , Drosophila Proteins/chemistry , Drosophila melanogaster/cytology , Drosophila melanogaster/embryology , Drosophila melanogaster/genetics , Embryo, Nonmammalian/cytology , Embryo, Nonmammalian/metabolism , Gene Expression Regulation, Developmental , Homeodomain Proteins/chemistry , Models, Biological , Molecular Sequence Data , Protein Transport , Regulatory Sequences, Nucleic Acid , Repressor Proteins/metabolism , Sequence Deletion , Transcription Factors/chemistryABSTRACT
Gene regulation by AP-1 transcription factors in response to Jun N-terminal kinase (JNK) signaling controls essential cellular processes during development and in pathological situations. Here, we report genetic and molecular evidence that the histone acetyltransferase (HAT) Chameau and the histone deacetylase DRpd3 act as antagonistic cofactors of DJun and DFos to modulate JNK-dependent transcription during thorax metamorphosis and JNK-induced apoptosis in Drosophila. We demonstrate in cultured cells that DFos phosphorylation mediated by JNK signaling plays a central role in coordinating the dynamics of Chameau and DRpd3 recruitment and function at AP-1-responsive promoters. Activating the pathway stimulates the HAT function of Chameau, promoting histone H4 acetylation and target gene transcription. Conversely, in response to JNK signaling inactivation, DRpd3 is recruited and suppresses histone acetylation and transcription. This study establishes a direct link among JNK signaling, DFos phosphorylation, chromatin modification, and AP-1-dependent transcription and its importance in a developing organism.
Subject(s)
Acetyltransferases/physiology , Drosophila Proteins/physiology , Drosophila/physiology , Histone Deacetylases/physiology , MAP Kinase Kinase 4/physiology , Repressor Proteins/physiology , Transcription Factor AP-1/physiology , Transcription Factors/physiology , Acetylation , Acetyltransferases/metabolism , Animals , Apoptosis , Cells, Cultured , Chromatin Assembly and Disassembly , Drosophila/genetics , Drosophila Proteins/metabolism , Histone Deacetylase 1 , Histone Deacetylases/metabolism , Histones/metabolism , Humans , Metamorphosis, Biological , Phosphorylation , Promoter Regions, Genetic , Repressor Proteins/metabolism , Signal Transduction , Transcription Factors/metabolism , Transcription, GeneticABSTRACT
The transcription factor dMyc is the sole Drosophila ortholog of the vertebrate c-myc protooncogenes and a central regulator of growth and cell-cycle progression during normal development. We have investigated the molecular basis of dMyc function by analyzing its interaction with the putative transcriptional cofactors Tip48/Reptin (Rept) and Tip49/Pontin (Pont). We demonstrate that Rept and Pont have conserved their ability to bind to Myc during evolution. All three proteins are required for tissue growth in vivo, because mitotic clones mutant for either dmyc, pont,or rept suffer from cell competition. Most importantly, pont shows a strong dominant genetic interaction with dmyc that is manifested in the duration of development, rates of survival and size of the adult animal and, in particular, of the eye. The molecular basis for these effects may be found in the repression of certain target genes, such as mfas, by dMyc:Pont complexes. These findings indicate that dMyc:Pont complexes play an essential role in the control of cellular growth and proliferation during normal development.
Subject(s)
Carrier Proteins/genetics , DNA Helicases/genetics , DNA Helicases/physiology , Drosophila Proteins/genetics , Drosophila melanogaster/growth & development , Drosophila melanogaster/genetics , Proto-Oncogene Proteins c-myc/genetics , Animals , Animals, Genetically Modified , Carrier Proteins/metabolism , Cell Line , Cell Proliferation , DNA Helicases/deficiency , DNA Helicases/metabolism , Drosophila Proteins/deficiency , Drosophila Proteins/metabolism , Drosophila Proteins/physiology , Drosophila melanogaster/cytology , Drosophila melanogaster/metabolism , Eye/growth & development , Eye/metabolism , Mutation/genetics , Phenotype , Protein Binding , Proto-Oncogene Proteins c-myc/metabolismABSTRACT
Hox genes encode evolutionarily conserved transcription factors with key functions in development and evolution. Although the multitude of processes individually controlled by Hox proteins highlights the importance of contextual information in setting their diverse activities, the underlying molecular mechanisms still remain elusive. A recent study identified novel Hox molecular partners, whose properties set a conceptual framework to understand how Hox proteins use and integrate contextual information.
Subject(s)
Genes, Homeobox , Homeodomain Proteins/physiology , Animals , Body Patterning/physiology , Drosophila/embryology , Drosophila/physiology , Drosophila Proteins/genetics , Drosophila Proteins/physiology , Gene Expression Regulation, Developmental , Homeodomain Proteins/genetics , Protein Binding , Transcription Factors/genetics , Transcription Factors/physiologyABSTRACT
Evolutionarily conserved from yeast to human, the paralogous DNA helicases Pontin (Pont) and Reptin (Rept) are simultaneously recruited in multi-protein chromatin complexes that function in different aspects of DNA metabolism (transcription, replication and repair). When assayed, the two proteins were found to be essential for viability and to play antagonistic roles, suggesting that the balance of Pont/Rept regulates epigenetic programmes critical for development. Consistent with this, the two helicases are provided in the same embryonic territories during Drosophila development. In Xenopus, while transcribed in the same regions early in embryogenesis, pont and rept adopt significantly different patterns afterwards. Here we report that the two genes follow highly resembling transcription patterns in mouse embryos, with prominent expression in limb buds and branchial arches, organs undergoing mesenchymal-epithelial interactions and in motoneurones from cranial and spinal regions. Thus, simultaneous expression during development appears to constitute another feature of the evolutionary conservation of pont and rept genes.
Subject(s)
DNA Helicases/genetics , Gene Expression Regulation, Developmental/physiology , Animals , DNA Helicases/biosynthesis , In Situ Hybridization , Mice , Organ Specificity/geneticsABSTRACT
Hox proteins provide axial positional information and control segment morphology in development and evolution. Yet how they specify morphological traits that confer segment identity and how axial positional information interferes with intrasegmental patterning cues during organogenesis remain poorly understood. We have investigated the control of Drosophila posterior spiracle morphogenesis, a segment-specific structure that forms under Abdominal-B (AbdB) Hox control in the eighth abdominal segment (A8). We show that the Hedgehog (Hh), Wingless (Wg) and Epidermal Growth Factor Receptor (Egfr) pathways provide specific inputs for posterior spiracle morphogenesis and act in a genetic network made of multiple and rapidly evolving Hox/signalling interplays. A major function of AbdB during posterior spiracle organogenesis is to reset A8 intrasegmental patterning cues, first by reshaping wg and rhomboid expression patterns, then by reallocating the Hh signal and later by initiating de novo expression of the posterior compartment gene engrailed in anterior compartment cells. These changes in expression patterns confer axial specificity to otherwise reiteratively used segmental patterning cues, linking intrasegmental polarity and acquisition of segment identity.
Subject(s)
Body Patterning/physiology , Drosophila melanogaster/embryology , Homeodomain Proteins/physiology , Organogenesis/genetics , Animals , Body Patterning/genetics , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila melanogaster/genetics , Ectoderm/physiology , ErbB Receptors/metabolism , Gene Expression Regulation, Developmental/physiology , Hedgehog Proteins , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Membrane Proteins/genetics , Membrane Proteins/metabolism , Organogenesis/physiology , Protein Kinases/metabolism , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Receptors, Invertebrate Peptide/metabolism , Signal Transduction/physiology , Transcription Factors/genetics , Transcription Factors/metabolism , Wnt1 ProteinABSTRACT
Hox proteins play fundamental roles in generating pattern diversity during development and evolution, acting in broad domains but controlling localized cell diversification and pattern. Much remains to be learned about how Hox selector proteins generate cell-type diversity. In this study, regulatory specificity was investigated by dissecting the genetic and molecular requirements that allow the Hox protein Abdominal A to activate wingless in only a few cells of its broad expression domain in the Drosophila visceral mesoderm. We show that the Dpp/Tgfbeta signal controls Abdominal A function, and that Hox protein and signal-activated regulators converge on a wingless enhancer. The signal, acting through Mad and Creb, provides spatial information that subdivides the domain of Abdominal A function through direct combinatorial action, conferring specificity and diversity upon Abdominal A activity.
Subject(s)
DNA-Binding Proteins , Drosophila Proteins/metabolism , Drosophila/embryology , Homeodomain Proteins/metabolism , Nuclear Proteins , Signal Transduction/physiology , Transforming Growth Factor beta/metabolism , Activating Transcription Factor 1 , Animals , Drosophila Proteins/biosynthesis , Drosophila Proteins/genetics , Enhancer Elements, Genetic , Gene Expression Regulation, Developmental , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Proto-Oncogene Proteins/biosynthesis , Proto-Oncogene Proteins/genetics , Transcription Factors/metabolism , Wnt1 ProteinABSTRACT
In Drosophila, the homologue of the proto-oncogene Myc is a key regulator of both cell size and cell growth. The identities and roles of dMyc target genes in these processes, however, remain largely unexplored. Here, we investigate the function of the modulo (mod) gene, which encodes a nucleolus localized protein. In gain of function or loss of function experiments, we demonstrate that mod is directly controlled by dMyc. Strikingly, in proliferative imaginal cells, mod loss-of-function impairs both cell growth and cell size, whereas larval endoreplicative tissues grow normally. In contrast to dMyc, over-expressing Mod in wing imaginal discs is not sufficient to induce cell growth. Taken together, our results indicate that mod does not possess the full spectrum of dMyc activities, but is required selectively in proliferative cells to sustain their growth and to maintain their specific size.
Subject(s)
Cell Division/physiology , DNA-Binding Proteins/metabolism , Drosophila Proteins/metabolism , Drosophila/metabolism , Proto-Oncogene Proteins c-myc/metabolism , RNA-Binding Proteins/metabolism , Animals , Base Sequence , Cell Nucleolus/metabolism , DNA-Binding Proteins/genetics , Drosophila/growth & development , Drosophila Proteins/genetics , E-Box Elements , Gene Expression Regulation , Larva/growth & development , Larva/metabolism , Molecular Sequence Data , Promoter Regions, Genetic , RNA-Binding Proteins/geneticsABSTRACT
The Hox family transcription factors control diversified morphogenesis during development and evolution. They function in concert with Pbc cofactor proteins. Pbc proteins bind the Hox hexapeptide (HX) motif and are thereby thought to confer DNA binding specificity. Here we report that mutation of the AbdA HX motif does not alter its binding site selection but does modify its transregulatory properties in a gene-specific manner in vivo. We also show that a short, evolutionarily conserved motif, PFER, in the homeodomain-HX linker region acts together with the HX to control an AbdA activation/repression switch. Our in vivo data thus reveal functions not previously anticipated from in vitro analyses for the hexapeptide motif in the regulation of Hox activity.
Subject(s)
Drosophila Proteins/chemistry , Drosophila Proteins/metabolism , Drosophila melanogaster/embryology , Drosophila melanogaster/metabolism , Gene Expression Regulation, Developmental , Homeodomain Proteins/chemistry , Homeodomain Proteins/metabolism , Nerve Tissue Proteins/chemistry , Nerve Tissue Proteins/metabolism , Nuclear Proteins , Amino Acid Motifs , Amino Acid Sequence , Animals , Conserved Sequence , DNA Footprinting , Drosophila melanogaster/genetics , Electrophoretic Mobility Shift Assay , In Situ Hybridization , Mesoderm/metabolism , Molecular Sequence Data , Sequence Homology, Amino Acid , Transcription Factors/metabolismABSTRACT
Hox genes encode evolutionarily conserved transcription factors that play fundamental roles in the organization of the animal body plan. Molecular studies emphasize that unidentified genes contribute to the control of Hox activity. In this study, we describe a genetic screen designed to identify functions required for the control of the wingless (wg) and empty spiracles (ems) target genes by the Hox Abdominal-A and Abdominal-B proteins. A collection of chromosomal deficiencies were screened for their ability to modify GFP fluorescence patterns driven by Hox response elements (HREs) from wg and ems. We found 15 deficiencies that modify the activity of the ems HRE and 18 that modify the activity of the wg HRE. Many deficiencies cause ectopic activity of the HREs, suggesting that spatial restriction of transcriptional activity is an important level in the control of Hox gene function. Further analysis identified eight loci involved in the homeotic regulation of wg or ems. A majority of these modifier genes correspond to previously characterized genes, although not for their roles in the regulation of Hox targets. Five of them encode products acting in or in connection with signal transduction pathways, which suggests an extensive use of signaling in the control of Hox gene function.