What's new in edition 47 part 3/5 September 2006 F-M

Updates at previously included gene sites:

genes F-M listed below

Fat Fear of intimacy Flamingo Frizzled Fused Gcn5/Pcaf Grunge H15 and Midline

Hairless Hedgehog Hemipterous HNF4 Huckebein Hunchback Jing Lethal of Scute

What's new in edition 47:
part 1/5 new genes | updates: part 2/5 genes A-E | part 4/5 genes N-R | part 5/5 genes S-Z

Fat: Fat and Wingless signaling oppositely regulate epithelial cell-cell adhesion and distal wing development

Development of organ-specific size and shape demands tight coordination between tissue growth and cell-cell adhesion. Dynamic regulation of cell adhesion proteins thus plays an important role during organogenesis. In Drosophila, the homophilic cell adhesion protein DE-Cadherin regulates epithelial cell-cell adhesion at adherens junctions (AJs). This study shows that along the proximodistal (PD) axis of the developing wing epithelium, apical cell shapes and expression of DE-Cad are graded in response to Wingless, a morphogen secreted from the dorsoventral (DV) organizer in distal wing, suggesting a PD gradient of cell-cell adhesion. The Fat (Ft) tumor suppressor, by contrast, represses DE-Cad expression. In genetic tests, ft behaves as a suppressor of Wg signaling. Cytoplasmic pool of ß-catenin/Arm, the intracellular transducer of Wg signaling, is negatively correlated with the activity of Ft. Moreover, unlike that of Wg, signaling by Ft negatively regulates the expression of Distalless (Dll) and Vestigial (Vg). Finally, Ft is shown to intersect Wnt/Wg signaling, downstream of the Wg ligand. Fat and Wg signaling thus exert opposing regulation to coordinate cell-cell adhesion and patterning along the PD axis of Drosophila wing (Jaiswal, 2006).

Fear of intimacy: Zinc transport activity of Fear of Intimacy is essential for proper gonad morphogenesis and DE-cadherin expression

Embryonic gonad formation involves intimate contact between germ cells and specialized somatic cells along with the complex morphogenetic movements necessary to create proper gonad architecture. Gonad formation in Drosophila requires the homophilic cell-adhesion molecule Drosophila E-cadherin (DE-cadherin), and also Fear of Intimacy (FOI), which is required for stable accumulation of DE-cadherin protein in the gonad. In vivo structure-function analysis is presented of FOI that strongly indicates that zinc transport activity of FOI is essential for gonad development. Mutant forms of FOI that are defective for zinc transport also fail to rescue morphogenesis and DE-cadherin expression in the gonad. Expression of DE-cadherin in the gonad is regulated post-transcriptionally and foi affects this post-transcriptional control. Expression of DE-cadherin from a ubiquitous (tubulin) promoter still results in gonad-specific accumulation of DE-cadherin, which is strongly reduced in foi mutants. This work indicates that zinc is a crucial regulator of developmental processes and can affect DE-cadherin expression on multiple levels (Mathews, 2006).

Flamingo: Potential dual molecular interaction of the Drosophila 7-pass transmembrane cadherin Flamingo in dendritic morphogenesis

Seven-pass transmembrane cadherins (7-TM cadherins) play pleiotropic roles in epithelial planar cell polarity, shaping dendritic arbors and in axonal outgrowth. In contrast to their role in planar polarity, how 7-TM cadherins control dendritic and axonal outgrowth at the molecular level is largely unknown. Therefore, extensive structure-function analysis was performed of the Drosophila 7-TM cadherin Flamingo (Fmi), and the activities of individual mutant forms were investigated mostly in dendritogenesis of dendritic arborization (da) neurons. One of the fmi-mutant phenotypes was overgrowth of branches in the early stage of dendrite development. In da neurons but not in their adjacent non-neuronal cells, expression of a truncated form (DeltaN) that lacks the entire cadherin repeat sequence, rescues flies (at least partially) from this phenotype. The truncated form still retains HRM (hormone-receptor domain), a motif of about 60 amino acids long conserved in the subfamily of G-protein coupled receptors (GPCRs); conserved cysteine residues in HRM have been implicated in transmitting signals of ligand binding to intracellular components. The HRM of the truncated protein might still be able to interact with a yet-to-be-identified ligand and therefore be able to limit branch elongation (Kimura, 2006).

Frizzled: Polarized transport of Frizzled along the planar microtubule arrays in Drosophila wing epithelium

Cells in a variety of developmental contexts sense extracellular cues that are given locally on their surfaces, and subsequently amplify the initial signal to achieve cell polarization. Drosophila wing cells acquire planar polarity along the proximal-distal (P-D) axis, in which the amplification of the presumptive cue involves assembly of a multiprotein complex that spans distal and proximal boundaries of adjacent cells. This study pursues the mechanisms that place one of the components, Frizzled (Fz), at the distal side. Intracellular particles of GFP-tagged Fz move preferentially toward distal boundaries before Fz::GFP and other components are tightly localized at the P/D cortex. Arrays of microtubules (MTs) are approximately oriented along the P-D axis and these MTs contribute to the formation of the cortical complex. Furthermore, there appears to be a bias in the P-D MTs, with slightly more plus ends oriented distally. The hypothesis of polarized vesicular trafficking of Fz is discussed (Shimada, 2006).

Fused: fused regulates germline cyst mitosis and differentiation during Drosophila oogenesis

The fused gene encodes a serine-threonine kinase that functions as a positive regulator of Hedgehog signal transduction in Drosophila embryogenesis, wing morphogenesis, and somatic cell development during oogenesis. This study characterizes the germline ovarian tumors present in adult ovaries of fused mutant females, a phenotype not observed upon deregulation of any other component of Hedgehog signaling. In the strongest fused mutant contexts, tumorous ovarian follicles accumulate early spectrosome-containing germ cells corresponding to germline stem cells and/or early cystoblasts as evidenced by activated Dpp signal transduction and transcriptional repression of bag-of-marbles, encoding the cystoblast determination factor. These early germ cells are maintained far from their usual position in a specialized niche of somatic cells in the apical part of the germarium, which appears normal in size in fused mutant ovarioles. Therefore, these results indicate a novel function for fused in downregulation of Dpp signaling; this is necessary for de-repression of bag-of-marbles and consequent cystoblast determination. The abnormal accumulation of these early germ cells seems to be due primarily to defects in differentiation, since germline stem cell proliferation in the germarium is not affected. A later block in germline development, at the 16-cell cyst stage before significant nurse cell and oocyte differentiation, is also observed in tumorous follicles when fused function is only partially lowered. Finally, fused mutant ovaries exhibit some germline cysts having undergone a supernumerary fifth mitotic division. Through clonal analysis, evidence is provided that fused regulates these cystocyte divisions cell autonomously, while the tumorous phenotype probably reflects both a somatic and germline requirement of fused for cyst and follicle development (Narbonne-Reveau, 2006).

Gcn5/Pcaf: Host cell factor and an uncharacterized SANT domain protein are stable components of ATAC, a novel dAda2A/dGcn5-containing histone acetyltransferase complex in Drosophila

Gcn5 is a conserved histone acetyltransferase (HAT) found in a number of multisubunit complexes from Saccharomyces cerevisiae, mammals, and flies. Drosophila melanogaster homologues of the yeast proteins Ada2, Ada3, Spt3, and Tra1 have been identified and they have been shown to associate with dGcn5 to form at least two distinct HAT complexes. There are two different Ada2 homologues in Drosophila named dAda2A and dAda2B. dAda2B functions within the Drosophila version of the SAGA complex (dSAGA). To gain insight into dAda2A function, novel components have been sought of the complex containing this protein, ATAC (Ada two A containing) complex. Affinity purification and mass spectrometry revealed that, in addition to dAda3 and dGcn5, host cell factor (dHCF) and a novel SANT domain protein, named Atac1 (ATAC component 1), copurify with this complex. Coimmunoprecipitation experiments confirmed that these proteins associate with dGcn5 and dAda2A, but not with dSAGA-specific components such as dAda2B and dSpt3. Biochemical fractionation revealed that ATAC has an apparent molecular mass of 700 kDa and contains dAda2A, dGcn5, dAda3, dHCF, and Atac1 as stable subunits. Thus, ATAC represents a novel histone acetyltransferase complex that is distinct from previously purified Gcn5/Pcaf-containing complexes from yeast and mammalian cells (Guelman, 2006).

Grunge: Atrophin contributes to the negative regulation of epidermal growth factor receptor signaling in Drosophila

Dentato-rubral and pallido-luysian atrophy (DRPLA) is a dominant, progressive neurodegenerative disease caused by the expansion of polyglutamine repeats within the human Atrophin-1 protein. Drosophila Atrophin and its human orthologue are thought to function as transcriptional co-repressors. Drosophila Atrophin participates in the negative regulation of Epidermal Growth Factor Receptor (EGFR) signaling both in the wing and the eye imaginal discs. In the wing pouch, Atrophin loss of function clones induces cell autonomous expression of the EGFR target gene Delta, and the formation of extra vein tissue, while overexpression of Atrophin inhibits EGFR-dependent vein formation. In the eye, Atrophin cooperates with other negative regulators of the EGFR signaling to prevent the differentiation of surplus photoreceptor cells and to repress Delta expression. Overexpression of Atrophin in the eye reduces the EGFR-dependent recruitment of cone cells. In both the eye and wing, epistasis tests show that Atrophin acts downstream or in parallel to the MAP kinase rolled to modulate EGFR signaling outputs. Atrophin genetically cooperates with the nuclear repressor Yan to inhibit the EGFR signaling activity. Finally, it was found that expression of pathogenic or normal forms of human Atrophin-1 in the wing promotes wing vein differentiation and these forms act as dominant negative proteins inhibiting endogenous fly Atrophin activity (Charroux, 2006).

H15 and Midline: Functions of the segment polarity genes midline and H15 in Drosophila melanogaster neurogenesis

The Drosophila ventral nerve cord derives from neural progenitor cells called neuroblasts. Individual neuroblasts have unique gene expression profiles and give rise to distinct clones of neurons and glia. The specification of neuroblast identity provides a cell intrinsic mechanism that ultimately results in the generation of progeny which are different from one another. Segment polarity genes have a dual function in early neurogenesis: within distinct regions of the neuroectoderm, they are required both for neuroblast formation and for the specification of neuroblast identity. Previous studies of segment polarity gene function largely focused on neuroblasts that arise within the posterior part of the segment. This study shows that the segment polarity gene midline is required for neuroblast formation in the anterior-most part of the segment. Moreover, midline contributes to the specification of anterior neuroblast identity by negatively regulating the expression of Wingless and positively regulating the expression of Mirror. In the posterior-most part of the segment, midline and its paralog, H15, have partially redundant functions in the regulation of the NB marker Eagle. Hence, the segment polarity genes midline and H15 play an important role in the development of the ventral nerve cord in the anterior- and posterior-most part of the segment (Buescher, 2006).

Hairless: A molecular link between Hairless and Pros26.4, a member of the AAA-ATPase subunits of the proteasome 19S regulatory particle in Drosophila

The proteasome is the major degradation machinery of the cell that regulates multiple cellular processes as diverse as cell cycle, signal transduction and gene expression. Recognition and unfolding of target proteins involves the regulatory cap whose base contains six AAA-ATPases that display reverse chaperone activity. One of them, Rpt2 (also known as S4), has an essential role in gating the degradative central core. The orthologous gene Pros26.4 has been isolated from Drosophila melanogaster as a molecular interaction partner of Hairless. Hairless plays a major role as antagonist of Notch signalling in Drosophila, prompting an interest in the Hairless-Pros26.4 interaction. Pros26.4 negatively regulates Hairless at the genetic and molecular level. Depletion of Pros26.4 by using tissue-specific RNA interference (RNAi) results in a specific stabilization of the Hairless protein, but not in stabilization of the intracellular domain of Notch or the effector protein Suppressor of Hairless. Thus, the Hairless-Pros26.4 interaction provides a novel mechanism of positive regulation of Notch signalling (Muller, 2006).

Hedgehog: Cholesterol modification is necessary for controlled planar long-range activity of Hedgehog in Drosophila epithelia

The Hedgehog morphogen is a major developmental regulator that acts at short and long range to direct cell fate decisions in invertebrate and vertebrate tissues. Hedgehog is the only known metazoan protein to possess a covalently linked cholesterol moiety. Although the role of the cholesterol group of Hedgehog remains unclear, it has been suggested to be dispensable for the its long-range activity in Drosophila. This study provides data in three different epithelia -- ventral and dorsal embryonic ectoderm, and larval imaginal disc tissue -- showing that cholesterol modification is in fact necessary for the controlled long-range activity of Drosophila Hedgehog. An explanation is provided for the discrepancy between the current results and previous reports by showing that unmodified Hh can act at long range, albeit in an uncontrolled manner, only when expressed in squamous cells. These data show that cholesterol modification controls long-range Hh activity at multiple levels. Initially, cholesterol increases the affinity of Hh for the plasma membrane, and consequently enhances its apparent intrinsic activity, both in vitro and in vivo. In addition, multimerisation of active Hh requires the presence of cholesterol. These multimers are correlated with the assembly of Hh into apically located, large punctate structures present in active Hh gradients in vivo. By comparing the activity of cholesterol-modified Hh in columnar epithelial cells and peripodial squamous cells, this study shows that epithelial cells provide the machinery necessary for the controlled planar movement of Hh, thereby preventing the unrestricted spreading of the protein within the three-dimensional space of the epithelium. It is concluded that, as in vertebrates, cholesterol modification is essential for controlled long-range Hh signalling in Drosophila (Gallet, 2006).

Hedgehog: Hedgehog lipid modifications are required for Hedgehog stabilization in the extracellular matrix

The Hedgehog (Hh) family of morphogenetic proteins has important instructional roles in metazoan development. Despite Hh being modified by Ct-cholesterol and Nt-palmitate adducts, Hh migrates far from its site of synthesis and programs cellular outcomes, depending on its local concentrations. In the receiving cells of the Drosophila wing imaginal disc, lipid-unmodified Hh spreads across many more cell diameters than the wild type and this spreading leads to the activation of low but not high threshold responses. Unlipidated Hh forms become internalized through the apical plasma membrane, while wild-type Hh enters through the basolateral cell surface -- in all cases via a dynamin-dependent mechanism. Full activation of the Hh pathway and the spread of Hh throughout the extracellular matrix depend on the ability of lipid-modified Hh to interact with heparan sulfate proteoglycans (HSPG). However, neither Hh-lipid modifications nor HSPG function are required to activate the targets that respond to low levels of Hh. All these data show that the interaction of lipid-modified Hh with HSPG is important both for precise Hh spreading through the epithelium surface and for correct Hh reception (Callejo, 2006).

Hemipterous: Protein Interactions

Many bacterial toxins act on conserved components of essential host-signaling pathways. One consequence of this conservation is that genetic model organisms such as Drosophila can be used for analyzing the mechanism of toxin action. In this study, the activities of two anthrax virulence factors, lethal factor (LF) and edema factor, were characterized in transgenic Drosophila. LF is a zinc metalloprotease that cleaves and inactivates most human mitogen-activated protein kinase (MAPK) kinases (MAPKKs). LF similarly cleaves the Drosophila MAPK kinases Hemipterous (Hep) and Licorne in vitro. Consistent with these observations, expression of LF in Drosophila inhibited the Hep/c-Jun N-terminal kinase pathway during embryonic dorsal closure and the related process of adult thoracic closure. Epistasis experiments confirmed that LF acts at the level of Hep. It was also found that LF inhibits Ras/MAPK signaling during wing development and that LF acts upstream of MAPK and downstream of Raf, consistent with LF acting at the level of Dsor. In addition, edema factor, a potent adenylate cyclase, inhibits the hh pathway during wing development, consistent with the known role of cAMP-dependent PKA in suppressing the Hedgehog response. These results demonstrate that anthrax toxins function in Drosophila as they do in mammalian cells and open the way to using Drosophila as a multicellular host system for studying the in vivo function of diverse toxins and virulence factors (Guichard, 2006).

HNF4: A modified tandem affinity purification strategy identifies cofactors of the Drosophila nuclear receptor dHNF4

With the completion of numerous genome projects, new high-throughput methods are required to ascribe gene function and interactions. A method proven successful in yeast for protein interaction studies is tandem affinity purification (TAP) of native protein complexes followed by MS. TAP, using Protein A and CBP tags, is not generally suitable for the purification and identification of proteins from tissues. A head-to-head comparison of tags shows that two others, FLAG and His, provide protein yields from Drosophila tissues that are an order of magnitude higher than Protein A and CBP. FLAG-His purification works sufficiently well so that two cofactors of the Drosophila nuclear receptor protein dHNF4 could be purified from whole animals. These proteins, Hsc70 and Hsp83, are important chaperones and cofactors of other nuclear receptor proteins. However, this is the first time that they have been shown to interact with a non-steroid binding nuclear receptor. The two proteins increase the ability of dHNF4 to bind DNA in vitro and to function in vivo. The tags and approaches developed here will help facilitate the routine purification of proteins from complex cells, tissues and whole organisms (Yang, 2006).

Huckebein: Huckebein-mediated autoregulation of Glide/Gcm triggers glia specification

Cell specification in the nervous system requires patterning genes dictating spatio-temporal coordinates as well as fate determinants. In the case of neurons, which are controlled by the family of proneural transcription factors, binding specificity and patterned expression trigger both differentiation and specification. In contrast, a single gene, glial cell missing (gcm), is sufficient for all fly lateral glial differentiation. How can different types of cells develop in the presence of a single fate determinant? That is, how do differentiation and specification pathways integrate and produce distinct glial populations? By following an identified lineage, this study shows that glia specification is triggered by gcm expression levels, mediated by cell-specific protein-protein interactions. Huckebein (Hkb), a lineage-specific factor, provides a molecular link between gcm and positional cues. Importantly, Hkb does not activate transcription; rather, it physically interacts with Gcm thereby triggering its autoregulation. These data emphasize the importance of fate determinant cell-specific quantitative regulation in the establishment of cell diversity (De Iaco, 2006).

Hunchback: Regulation of neuroblast competence: multiple temporal identity factors specify distinct neuronal fates within a single early competence window

Cellular competence is an essential but poorly understood aspect of development. Is competence a general property that affects multiple signaling pathways (e.g., chromatin state), or is competence specific for each signaling pathway (e.g., availability of cofactors)? This study has found that (1) Drosophila neuroblast 7-1 (NB7-1) has a single early window of competence to respond to four different temporal identity genes (Hunchback, Krüppel, Pdm, and Castor); (2) each of these factors specifies distinct motor neuron identities within this competence window but not outside it, and (3) progressive restriction to respond to Hunchback and Krüppel occurs within this window. This work raises the possibility that multiple competence windows may allow the same factors to generate different cell types within the same lineage (Cleary, 2006).

Hunchback: Timing of identity: spatiotemporal regulation of hunchback in neuroblast lineages of Drosophila by Seven-up and Prospero

Neural stem cells often generate different cell types in a fixed birth order as a result of temporal specification of the progenitors. In Drosophila, the first temporal identity of most neural stem cells (neuroblasts) in the embryonic ventral nerve cord is specified by the transient expression of the transcription factor Hunchback. When reaching the next temporal identity, this expression is switched off in the neuroblasts by seven up (svp) in a mitosis-dependent manner, but is maintained in their progeny (ganglion mother cells). svp mRNA is already expressed in the neuroblasts before this division. After mitosis, Svp protein accumulates in both cells, but the downregulation of hunchback (hb) occurs only in the neuroblast. In the ganglion mother cell, svp is repressed by Prospero, a transcription factor asymmetrically localised to this cell during mitosis. Thus, the differential regulation of hb between the neuroblasts and the ganglion mother cells is achieved by a mechanism that integrates information created by the asymmetric distribution of a cell-fate determinant upon mitosis (Prospero) and a transcriptional repressor present in both cells (Seven-up). Strikingly, although the complete downregulation of hb is mitosis dependent, the lineage-specific timing of svp upregulation is not (Mettler, 2006).

Jing: Protein Interactions

Neuronal-glial communication is essential for constructing the orthogonal axon scaffold in the developing Drosophila central nervous system (CNS). Longitudinal glia (LG) guide extending commissural and longitudinal axons while pioneer and commissural neurons maintain glial survival and positioning. However, the transcriptional regulatory mechanisms controlling these processes are not known. The midline function of the jing C2H2-type zinc finger transcription factor has been shown to be only partially required for axon scaffold formation in the Drosophila CNS. A screen was performed for gain-of-function enhancers of jing gain-of-function in the eye; the Drosophila homolog DATR-X (also termed XNP) of the disease gene of human alpha-thalassemia/mental retardation X-linked (ATR-X) was identified, as well as other genes with potential roles in gene expression, translation, synaptic transmission and cell cycle. jing and DATR-X reporter genes are expressed in both CNS neurons and glia including the longitudinal glia. Co-expression of jing and DATR-X in embryonic neurons synergistically affects longitudinal connective formation. During embryogenesis, jing and DATR-X have autonomous and non-autonomous roles in the lateral positioning of LG, neurons and longitudinal axons as shown by cell-specific knock-down of gene expression. jing and DATR-X are also required autonomously for glial survival. jing and DATR-X mutations show synergistic effects during longitudinal axon formation, suggesting they are functionally related. These observations support a model in which downstream gene expression (controlled by a potential DATR-X-Jing complex) facilitates cellular positioning and axon guidance, ultimately allowing for proper connectivity in the developing Drosophila CNS (Sun, 2006).

Jing: jing is required for wing development and to establish the proximo-distal axis of the leg in Drosophila

The establishment of the proximo-distal (PD) axis in the legs of Drosophila melanogaster requires the expression of a nested set of transcription factors that are activated in discreet domains by secreted signaling molecules. The precise regulation of these transcription factor domains is critical for generating the stereotyped morphological characteristics that exist along the PD axis, such as the positioning of specific bristle types and leg joints. Evidence is provided that the Zn-finger protein encoded by the gene jing is critical for PD axis formation in the Drosophila leg. The data suggest that jing represses transcription and that it is necessary to keep the proximal gene homothorax (hth) repressed in the medial domain of the PD axis. jing is also required for alula and vein development in the adult wing. In the wing, Jing is required to repress another proximal gene, teashirt (tsh), in a small domain that will give rise to the alula. Interestingly, two other genes affecting alula development, Alula and elbow, also exhibit tsh derepression in the same region of the wing disc as jing^- clones. Finally, jing is shown to genetically interact with several members of the Polycomb (Pc) group of genes during development. Together, these data suggest that jing encodes a transcriptional repressor that may participate in a subset of Pc-dependent activities during Drosophila appendage development (Culi, 2006).

Lethal of Scute: Determination of cell fate along the anteroposterior axis of the Drosophila ventral midline

The Drosophila ventral midline has proven to be a useful model for understanding the function of central organizers during neurogenesis. The midline is similar to the vertebrate floor plate, in that it plays an essential role in cell fate determination in the lateral CNS and also, later, in axon pathfinding. Despite the importance of the midline, the specification of midline cell fates is still not well understood. This study shows that most midline cells are determined not at the precursor cell stage, but as daughter cells. After the precursors divide, a combination of repression by Wingless and activation by Hedgehog induces expression of the proneural gene lethal of scute in the most anterior midline daughter cells of the neighbouring posterior segment. Hedgehog and Lethal of scute activate Engrailed in these anterior cells. Engrailed-positive midline cells develop into ventral unpaired median (VUM) neurons and the median neuroblast (MNB). Engrailed-negative midline cells develop into unpaired median interneurons (UMI), MP1 interneurons and midline glia (Bossing, 2006).

What's new in edition 47 of the Interactive Fly :

part 1/5 new genes | updates: part 2/5 genes A-E | part 4/5 genes N-R | part 5/5 genes S-Z

Home page: The Interactive Fly © 1995, 1996 Thomas B. Brody, Ph.D.