Coordinately and Differentially Mutable Activities of Torpedo, the Drosophila Melanogaster Homolog of the Vertebrate Egf Receptor Gene

The torpedo (top) locus of Drosophila encodes the fruitfly homolog of the vertebrate epidermal growth factor receptor gene and the neu proto-oncogene. We have isolated 13 top alleles in a screen for mutations failing to complement the female sterility of top, a recessive maternal effect allele that disrupts the establishment of the dorsoventral pattern of the egg shell and embryo. Several alleles recovered in this screen are zygotic lethal mutations; genetic analysis of these alleles has demonstrated that top is allelic to the embryonic lethal locus faint little ball. The 13 mutations recovered in our screens and 19 previously isolated top alleles have been genetically characterized through complementation tests with a series of hypomorphic and amorphic alleles. Nearly every top allele fails to complement the maternal effect sterility of top. Complementation tests show that the gene is required not only for oogenesis and embryogenesis, but also for pupal viability, for the growth of certain imaginal discs and for the patterning of specific ectodermal derivatives of the imaginal discs. Complementation analysis further demonstrates that the top lesions can be divided into general phenotypic categories: alleles affecting all gene activities in a coordinate manner, alleles preferentially affecting embryogenesis, alleles preferentially retaining oogenesis activity and alleles differentially affecting the development of specific imaginal disc derivatives. Correlations observed between the various developmental defects produced by top lesions suggest that the gene possesses several differentially, though not independently, mutable activities.     

Regulation of Stem Cell Proliferation and Cell Fate Specification by Wingless/Wnt Signaling Gradients Enriched at Adult Intestinal Compartment Boundaries

Intestinal stem cell (ISC) self-renewal and proliferation are directed by Wnt/β-catenin signaling in mammals, whereas aberrant Wnt pathway activation in ISCs triggers the development of human colorectal carcinoma. Herein, we have utilized the Drosophila midgut, a powerful model for ISC regulation, to elucidate the mechanisms by which Wingless (Wg)/Wnt regulates intestinal homeostasis and development. We provide evidence that the Wg signaling pathway, activation of which peaks at each of the major compartment boundaries of the adult intestine, has essential functions. Wg pathway activation in the intestinal epithelium is required not only to specify cell fate near compartment boundaries during development, but also to control ISC proliferation within compartments during homeostasis. Further, in contrast with the previous focus on Wg pathway activation within ISCs, we demonstrate that the primary mechanism by which Wg signaling regulates ISC proliferation during homeostasis is non-autonomous. Activation of the Wg pathway in absorptive enterocytes is required to suppress JAK-STAT signaling in neighboring ISCs, and thereby their proliferation. We conclude that Wg signaling gradients have essential roles during homeostasis and development of the adult intestine, non-autonomously controlling stem cell proliferation inside compartments, and autonomously specifying cell fate near compartment boundaries.     

Based on Molecular Profiling of Gene Expression,Palmoplantar Pustulosis and Palmoplantar Pustular Psoriasis Are Highly Related Diseases that Appear to Be Distinct from Psoriasis Vulgaris

IntroductionThere is a controversy surrounding the existence of palmoplantar pustulosis (PPP) and palmoplantar pustular psoriasis (PPPP) as separate clinical entities or as variants of the same clinical entity. We used gene expression microarray to compare gene expression in PPP and PPPP.

Methodology/Principal findings

Skin biopsies from subjects with PPP (3), PPPP (6), psoriasis vulgaris (10) and acral skin from normal subjects (7) were analyzed using gene expression microarray. Principal component analysis showed that PPP and PPPP were different from psoriasis vulgaris and normal acral skin. However gene expression of PPP and PPPP clustered together and could not be used to differentiate PPP from PPPP. Gene-wise comparison between PPP and PPPP found no gene to be differentially expressed at a false discovery rate lower than 0.05. Surprisingly we found a higher expression of several genes involved in neural pathways (e.g. GPRIN and ADAM23) in PPP/PPPP as compared to psoriasis vulgaris and normal acral skin. Immunohistochemistry confirmed those findings and showed a keratinocyte localization for those proteins.

Conclusion significance

PPP and PPPP could not be differentiated using gene expression microarray suggesting that they are not distinct clinical entities. Increased expression of GPRIN1, and ADAM23 in keratinocytes suggests that these proteins could be new therapeutic targets for PPP/PPPP.     

Signalling at a distance: transport of Wingless in the embryonic epidermis of Drosophila.

Secreted signalling molecules affect the behavior of cells at a distance. Here we discuss how the Wnt family member Wingless reaches distant cells within the embryonic epidermis of Drosophila.We consider three possible mechanisms: free diffusion, restricted diffusion and active transport. We argue that free diffusion is unlikely to occur. However, a variant of restricted diffusion may account for Wingless transport. It may be that Wingless is carried from one side of a cell to the other by a drifting transmembrane protein such as a specific receptor or a glycosaminoglycan. Transfer from cell-to-cell would involve release from the donor cell and recapture in an adjacent cell. Alternatively, Wingless might be transported by a mechanism akin to transcytosis. This would involve the packaging of Wingless in specialized vesicles at one end of a cell, active transport across the cell, and vesicle fusion and Wingless release on the other side. We describe the evidence in favor and against these two alternatives.     

Obstructor A Organizes Matrix Assembly at the Apical Cell Surface to Promote Enzymatic Cuticle Maturation in Drosophila

Assembly and maturation of the apical extracellular matrix (aECM) is crucial for protecting organisms, but underlying molecular mechanisms remain poorly understood. Epidermal cells secrete proteins and enzymes that assemble at the apical cell surface to provide epithelial integrity and stability during developmental growth and upon tissue damage. We analyzed molecular mechanisms of aECM assembly and identified the conserved chitin-binding protein Obst-A (Obstructor A) as an essential regulator. We show in Drosophila that Obst-A is required to coordinate protein and chitin matrix packaging at the apical cell surface during development. Secreted by epidermal cells, the Obst-A protein is specifically enriched in the apical assembly zone where matrix components are packaged into their highly ordered architecture. In obst-A null mutant larvae, the assembly zone is strongly diminished, resulting in severe disturbance of matrix scaffold organization and impaired aECM integrity. Furthermore, enzymes that support aECM stability are mislocalized. As a biological consequence, cuticle architecture, integrity, and function are disturbed in obst-A mutants, finally resulting in immediate lethality upon wounding. Our studies identify a new core organizing center, the assembly zone that controls aECM assembly at the apical cell surface. We propose a genetically conserved molecular mechanism by which Obst-A forms a matrix scaffold to coordinate trafficking and localization of proteins and enzymes in the newly deposited aECM. This mechanism is essential for maturation and stabilization of the aECM in a growing and remodeling epithelial tissue as an outermost barrier.     

Notch and Wingless modulate the response of cells to Hedgehog signalling in the Drosophila wing

During Drosophila wing development, Hedgehog (Hh) signalling is required to pattern the imaginal disc epithelium along the anterior-posterior (AP) axis. The Notch (N) and Wingless (Wg) signalling pathways organise the dorsal-ventral (DV) axis, including patterning along the presumptive wing margin. Here, we describe a functional hierarchy of these signalling pathways that highlights the importance of competing influences of Hh, N, and Wg in establishing gene expression domains. Investigation of the modulation of Hh target gene expression along the DV axis of the wing disc revealed that collier/knot (col/kn), patched (ptc), and decapentaplegic (dpp) are repressed at the DV boundary by N signalling. Attenuation of Hh signalling activity caused by loss of fused function results in a striking down-regulation of col, ptc, and engrailed (en) symmetrically about the DV boundary. We show that this down-regulation depends on activity of the canonical Wg signalling pathway. We propose that modulation of the response of cells to Hh along the future proximodistal (PD) axis is necessary for generation of the correctly patterned three-dimensional adult wing. Our findings suggest a paradigm of repression of the Hh response by N and/or Wnt signalling that may be applicable to signal integration in vertebrate appendages.     

EGFR Signaling Stimulates Autophagy to Regulate Stem Cell Maintenance and Lipid Homeostasis in the Drosophila Testis

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Wingless transduction by the Frizzled and Frizzled2 proteins of Drosophila.

Wingless (Wg) protein is a founding member of the Wnt family of secreted proteins which have profound organizing roles in animal development. Two members of the Frizzled (Fz) family of seven-pass transmembrane proteins, Drosophila Fz and Fz2, can bind Wg and are candidate Wg receptors. However, null mutations of the fz gene have little effect on Wg signal transduction and the lack of mutations in the fz2 gene has thus far prevented a rigorous examination of its role in vivo. Here we describe the isolation of an amber mutation of fz2 which truncates the coding sequence just after the amino-terminal extracellular domain and behaves genetically as a loss-of-function allele. Using this mutation, we show that Wg signal transduction is abolished in virtually all cells lacking both Fz and Fz2 activity in embryos as well as in the wing imaginal disc. We also show that Fz and Fz2 are functionally redundant: the presence of either protein is sufficient to confer Wg transducing activity on most or all cells throughout development. These results extend prior evidence of a ligand-receptor relationship between Wnt and Frizzled proteins and suggest that Fz and Fz2 are the primary receptors for Wg in Drosophila.     

Drosophila Tel2 Is Expressed as a Translational Fusion with EpsinR and Is a Regulator of Wingless Signaling

Tel2, a protein conserved from yeast to vertebrates, is an essential regulator of diverse cellular processes including telomere maintenance, DNA damage checkpoints, DNA repair, biological clocks, and cell signaling. The Drosophila Tel2 protein is produced as a translational fusion with EpsinR, a Clathrin adapter that facilitates vesicle trafficking between the Golgi and endosomes. EpsinR and Tel2 are encoded by a Drosophila gene called lqfR. lqfR is required for viability, and its specific roles include cell growth, proliferation, and planar cell polarity. We find that all of these functions of lqfR are attributed entirely to Tel2, not EpsinR. In addition, we find that Drosophila LqfR/Tel2 is a component of one or more protein complexes that contain E-cadherin and Armadillo. Moreover, Tel2 modulates E-cadherin and Armadillo cellular dynamics. We propose that at least one of the functions of Drosophila Tel2 is regulation of Wingless signaling.     

IgLON Cell Adhesion Molecules Are Shed from the Cell Surface of Cortical Neurons to Promote Neuronal Growth

Matrix metalloproteinases and a disintegrin and metalloproteinases are members of the zinc endopeptidases, which cleave components of the extracellular matrix as well as cell surface proteins resulting in degradation or release of biologically active fragments. Surface ectodomain shedding affects numerous biological processes, including survival, axon outgrowth, axon guidance, and synaptogenesis. In this study, we evaluated the role of metalloproteinases in regulating cortical neurite growth. We found that treatment of mature cortical neurons with pan-metalloproteinase inhibitors or with tissue inhibitors of metalloproteinase-3 reduced neurite outgrowth. Through mass spectrometry, we characterized the metalloproteinase-sensitive cell surface proteome of mature cortical neurons. Members of the IgLON family of glycosylphosphatidylinositol-anchored neural cell adhesion molecules were identified and validated as proteins that were shed from the surface of mature cortical neurons in a metalloproteinase-dependent manner. Introduction of two members of the IgLON family, neurotrimin and NEGR1, in early embryonic neurons was sufficient to confer sensitivity to metalloproteinase inhibitors in neurite outgrowth assays. Outgrowth experiments on immobilized IgLON proteins revealed a role for all IgLON family members in promoting neurite extension from cortical neurons. Together, our findings support a role for metalloproteinase-dependent shedding of IgLON family members in regulating neurite outgrowth from mature cortical neurons.     

Transvection at the Eyes Absent Gene of Drosophila

The Drosophila eyes absent (eya) gene is required for survival and differentiation of eye progenitor cells. Loss of gene function in the eye results in reduction or absence of the adult compound eye. Certain combinations of eya alleles undergo partial complementation, with dramatic restoration of eye size. This interaction is sensitive to the relative positions of the two alleles in the genome; rearrangements predicted to disrupt pairing of chromosomal homologs in the eya region disrupt complementation. Ten X-ray-induced rearrangements that suppress the interaction obey the same general rules as those tha disrupt transvection at the bithorax complex and the decapentaplegic gene. Moreover, like transvection in those cases, the interaction at eya depends on the presence of normal zeste function. The discovery of transvection at eya suggests that transvection interactions of this type may be more prevalent than generally thought.     

Control of Drosophila Blood Cell Activation via Toll Signaling in the Fat Body

The Toll signaling pathway, first discovered in Drosophila, has a well-established role in immune responses in insects as well as in mammals. In Drosophila, the Toll-dependent induction of antimicrobial peptide production has been intensely studied as a model for innate immune responses in general. Besides this humoral immune response, Toll signaling is also known to activate blood cells in a reaction that is similar to the cellular immune response to parasite infections, but the mechanisms of this response are poorly understood. Here we have studied this response in detail, and found that Toll signaling in several different tissues can activate a cellular immune defense, and that this response does not require Toll signaling in the blood cells themselves. Like in the humoral immune response, we show that Toll signaling in the fat body (analogous to the liver in vertebrates) is of major importance in the Toll-dependent activation of blood cells. However, this Toll-dependent mechanism of blood cell activation contributes very little to the immune response against the parasitoid wasp, Leptopilina boulardi, probably because the wasp is able to suppress Toll induction. Other redundant pathways may be more important in the defense against this pathogen.     

Copies of a Stellate Gene Variant Are Located in the X Heterochromatin of Drosophila Melanogaster and Are Probably Expressed

Two variants of X chromosome Stellate genes responsible for crystal formation in XO male primary spermatocytes occupy different genome positions. The majority if not all of the 1250-bp Stellate genes are located at the 12E site where the Ste locus has been mapped and almost all of the 1150-bp Stellate repeats are concentrated in the distal X heterochromatin. Sequencing of Stellate genes derived from X heterochromatin reveals the preservation of their open reading frames and precise matching with some Stellate cDNAs reported earlier. At least some heterochromatic Stellate genes are suggested to be expressed and, therefore, involved in the interaction with the Y chromosome locus Su(Ste), as are the Stellate genes from 12E.