Tracheal development in Drosophila melanogaster as a model system for studying the development of a branched organ

Emerging roles of MT-MMPs in embryonic development

Membrane-type matrix metalloproteinases (MT-MMPs) are cell membrane-tethered proteinases that belong to the family of the MMPs. Apart from their roles in degradation of the extracellular milieu, MT-MMPs are able to activate through proteolytic processing at the cell surface distinct molecules such as receptors, growth factors, cytokines, adhesion molecules, and other pericellular proteins. Although most of the information regarding these enzymes comes from cancer studies, our current knowledge about their contribution in distinct developmental processes occurring in the embryo is limited. In this review, we want to summarize the involvement of MT-MMPs in distinct processes during embryonic morphogenesis, including cell migration and proliferation, epithelial-mesenchymal transition, cell polarity and branching, axon growth and navigation, synapse formation, and angiogenesis. We also considered information about MT-MMP functions from studies assessed in pathological conditions and compared these data with those relevant for embryonic development.

Single-cell branching morphogenesis in the Drosophila trachea

The terminal cells of the tracheal epithelium in Drosophila melanogaster are one of the few known cell types that undergo subcellular morphogenesis to achieve a stable, branched shape. During the animal's larval stages, the cells repeatedly sprout new cytoplasmic processes. These grow very long, wrapping around target tissues to which the terminal cells adhere, and are hollowed by a gas-filled subcellular tube for oxygen delivery. Our understanding of this ramification process remains rudimentary. This review aims to provide a comprehensive summary of studies on terminal cells to date, and attempts to extrapolate how terminal branches might be formed based on the known genetic and molecular components. Next to this cell-intrinsic branching mechanism, we examine the extrinsic regulation of terminal branching by the target tissue and the animal's environment. Finally, we assess the degree of similarity between the patterns established by the branching programs of terminal cells and other branched cells and tissues from a mathematical and conceptual point of view.

Drosophila as a model for epithelial tube formation

Epithelial tubular organs are essential for life in higher organisms and include the pancreas and other secretory organs that function as biological factories for the synthesis and delivery of secreted enzymes, hormones, and nutrients essential for tissue homeostasis and viability. The lungs, which are necessary for gas exchange, vocalization, and maintaining blood pH, are organized as highly branched tubular epithelia. Tubular organs include arteries, veins, and lymphatics, high-speed passageways for delivery and uptake of nutrients, liquids, gases, and immune cells. The kidneys and components of the reproductive system are also epithelial tubes. Both the heart and central nervous system of many vertebrates begin as epithelial tubes. Thus, it is not surprising that defects in tube formation and maintenance underlie many human diseases. Accordingly, a thorough understanding how tubes form and are maintained is essential to developing better diagnostics and therapeutics. Among the best-characterized tubular organs are the Drosophila salivary gland and trachea, organs whose relative simplicity have allowed for in depth analysis of gene function, yielding key mechanistic insight into tube initiation, remodeling and maintenance. Here, we review our current understanding of salivary gland and trachea formation - highlighting recent discoveries into how these organs attain their final form and function.

Orthodenticle and empty spiracles genes are expressed in a segmental pattern in chelicerates

Members of the orthodenticle (otd/Otx) and empty spiracles (ems/Emx) gene families are head gap genes that encode homeodomain-containing DNA-binding proteins. Although numerous studies show their central role in developmental processes in brain specification, a surprisingly high number of other developmental processes have been shown to involve their expression. In this paper, we report the identification and expression of ems and otd in two chelicerate species: a scorpion, Euscorpius flavicaudis (Chactidae, Scorpiona, Arachnida, Euchelicerata) and a spider, Tegenaria saeva (Aranea, Arachnida, Euchelicerata). We show that both ems and otd are expressed not only in an anterior head domain but also along the entire anterior-posterior axis during embryonic development. The expression patterns for both genes are typically segmental and concern neurectodermal territories. During patterning of the opisthosoma, ems and otd are expressed in the lateral ectoderm just anterior to the limb bud primordia giving rise to respiratory organs and spinnerets (spider). This common pattern found in two divergent species thus appears to be a conserved character of chelicerates. These results are discussed in terms of evolutionary origin of respiratory organs and/or functional pathway recruitment.

Are Drosophila a useful model for understanding the toxicity of inhaled oxidative pollutants: a review

Oxidative atmospheric pollutants represent a significant stress and cause injury to both vertebrate and invertebrate species. In both, the biosurfaces of their respiratory apparatus are directly exposed to oxidizing pollutant-induced stresses. Respiratory-tract surfaces contain integrated antioxidant systems that appear to provide a primary defense against environmental insults caused by inhaled atmospheric reactive oxygen species (ROS) and reactive nitrogen species (RNS), whether gaseous or particulate. When the biosurface antioxidant defenses are overwhelmed, oxidative and nitrosative stress to the acellular and cellular components of the exposed biosurfaces can ensue via direct chemical reactions that lead to the induction of inflammatory, adaptive, injurious, and reparative processes. The study of model invertebrates (e.g., Drosophila) has a long history of yielding valuable insights into both fundamental biology and pathobiology. Mutants and/or transgenic insects, with specific alterations in key components of innate and/or adaptive antioxidant defense systems and immune genes, offer opportunities to dissect the complex systems that maintain respiratory tract surface defenses against environmental oxidants and the ensuing host responses. In this article, we use a comparative absfont approach to consider interactions of atmospheric oxidant pollutants with selected biosystems. We focused primarily on ozone (O(3)) as the pollutant, vertebrate and invertebrate respiratory tracts as the exposed biosystems, and nonenzymatic micronutrient antioxidants as significant contributors to overall antioxidant defense strategies. We present parallels among these diverse organisms with regard to their protective strategies against environmental atmospheric oxidants, with particular focus given to using the invertebrate Drosophila as a potentially useful model for vertebrate respiratory-tract responses to inhaled oxidants specifically and pollutants in general. We conclude that the insect respiratory system has considerable promise toward understanding novel aspects of vertebrate respiratory tract responses to inhaled oxidative environmental challenges.

Heparan sulphate proteoglycans: the sweet side of development

Pattern formation during development is controlled to a great extent by a small number of conserved signal transduction pathways that are activated by extracellular ligands such as Hedgehog, Wingless or Decapentaplegic. Genetic experiments have identified heparan sulphate proteoglycans (HSPGs) as important regulators of the tissue distribution of these extracellular signalling molecules. Several recent reports provide important new insights into the mechanisms by which HSPGs function during development.

Hairy transcriptional repression targets and cofactor recruitment in Drosophila

Members of the widely conserved Hairy/Enhancer of split family of basic Helix-Loop-Helix repressors are essential for proper Drosophila and vertebrate development and are misregulated in many cancers. While a major step forward in understanding the molecular mechanism(s) surrounding Hairy-mediated repression was made with the identification of Groucho, Drosophila C-terminal binding protein (dCtBP), and Drosophila silent information regulator 2 (dSir2) as Hairy transcriptional cofactors, the identity of Hairy target genes and the rules governing cofactor recruitment are relatively unknown. We have used the chromatin profiling method DamID to perform a global and systematic search for direct transcriptional targets for Drosophila Hairy and the genomic recruitment sites for three of its cofactors: Groucho, dCtBP, and dSir2. Each of the proteins was tethered to Escherichia coli DNA adenine methyltransferase, permitting methylation proximal to in vivo binding sites in both Drosophila Kc cells and early embryos. This approach identified 40 novel genomic targets for Hairy in Kc cells, as well as 155 loci recruiting Groucho, 107 loci recruiting dSir2, and wide genomic binding of dCtBP to 496 loci. We also adapted DamID profiling such that we could use tightly gated collections of embryos (2-6 h) and found 20 Hairy targets related to early embryogenesis. As expected of direct targets, all of the putative Hairy target genes tested show Hairy-dependent expression and have conserved consensus C-box-containing sequences that are directly bound by Hairy in vitro. The distribution of Hairy targets in both the Kc cell and embryo DamID experiments corresponds to Hairy binding sites in vivo on polytene chromosomes. Similarly, the distributions of loci recruiting each of Hairy's cofactors are detected as cofactor binding sites in vivo on polytene chromosomes. We have identified 59 putative transcriptional targets of Hairy. In addition to finding putative targets for Hairy in segmentation, we find groups of targets suggesting roles for Hairy in cell cycle, cell growth, and morphogenesis, processes that must be coordinately regulated with pattern formation. Examining the recruitment of Hairy's three characterized cofactors to their putative target genes revealed that cofactor recruitment is context-dependent. While Groucho is frequently considered to be the primary Hairy cofactor, we find here that it is associated with only a minority of Hairy targets. The majority of Hairy targets are associated with the presence of a combination of dCtBP and dSir2. Thus, the DamID chromatin profiling technique provides a systematic means of identifying transcriptional target genes and of obtaining a global view of cofactor recruitment requirements during development.

Functional characterization of Drosophila melanogaster peptide O-xylosyltransferase, the key enzyme for proteoglycan chain initiation and member of the core 2/I N-acetylglucosaminyltransferase family

Chondroitin and heparan sulfates are essential players in animal development and are synthesized by a series of glycosyltransferases, the first of which is UDP-alpha-D-xylose:proteoglycan core protein beta-D-xylosyltransferase (EC ). In the present study, a Drosophila melanogaster gene (CG17771), previously designated as a homologue of core 2 and I beta1,6-N-acetylglucosaminyltransferases, was shown to encode an active peptide O-xylosyltransferase. A novel coupled assay using matrix-assisted laser desorption ionization time-of-flight mass spectrometry demonstrated transfer of xylose to the peptide DDDSIEGSGGR. Analysis of sequences of various peptide O-xylosyltransferase and beta1,6-N-acetylglucosaminyltransferase sequences indicates that they are members of a large multifunctional protein family with a range of roles in beta-glycosylation of either peptide or glycan substrates. Because in contrast to mammals, there is only one fly peptide O-xylosyltransferase gene, it is anticipated that, given the key roles of proteoglycans, the hereby designated oxt gene is essential for viability.