Drosophila Eggshell Production: Identification of New Genes and Coordination by Pxt

Drosophila ovarian follicles complete development using a spatially and temporally controlled maturation process in which they resume meiosis and secrete a multi-layered, protective eggshell before undergoing arrest and/or ovulation. Microarray analysis revealed more than 150 genes that are expressed in a stage-specific manner during the last 24 hours of follicle development. These include all 30 previously known eggshell genes, as well as 19 new candidate chorion genes and 100 other genes likely to participate in maturation. Mutations in pxt, encoding a putative Drosophila cyclooxygenase, cause many transcripts to begin expression prematurely, and are associated with eggshell defects. Somatic activity of Pxt is required, as RNAi knockdown of pxt in the follicle cells recapitulates both the temporal expression and eggshell defects. One of the temporally regulated genes, cyp18a1, which encodes a cytochromome P450 protein mediating ecdysone turnover, is downregulated in pxt mutant follicles, and cyp18a1 mutation itself alters eggshell gene expression. These studies further define the molecular program of Drosophila follicle maturation and support the idea that it is coordinated by lipid and steroid hormonal signals

Identification of actinomycetes from plant rhizospheric soils with inhibitory activity against Colletotrichum spp., the causative agent of anthracnose disease

<p>Abstract</p> <p>Background</p> <p><it>Colletotrichum </it>is one of the most widespread and important genus of plant pathogenic fungi worldwide. Various species of <it>Colletotrichum </it>are the causative agents of anthracnose disease in plants, which is a severe problem to agricultural crops particularly in Thailand. These phytopathogens are usually controlled using chemicals; however, the use of these agents can lead to environmental pollution. Potential non-chemical control strategies for anthracnose disease include the use of bacteria capable of producing anti-fungal compounds such as actinomycetes spp., that comprise a large group of filamentous, Gram positive bacteria from soil. The aim of this study was to isolate actinomycetes capable of inhibiting the growth of <it>Colletotrichum </it>spp, and to analyze the diversity of actinomycetes from plant rhizospheric soil.</p> <p>Results</p> <p>A total of 304 actinomycetes were isolated and tested for their inhibitory activity against <it>Colletotrichum gloeosporioides </it>strains DoA d0762 and DoA c1060 and <it>Colletotrichum capsici </it>strain DoA c1511 which cause anthracnose disease as well as the non-pathogenic <it>Saccharomyces cerevisiae </it>strain IFO 10217. Most isolates (222 out of 304, 73.0%) were active against at least one indicator fungus or yeast. Fifty four (17.8%) were active against three anthracnose fungi and 17 (5.6%) could inhibit the growth of all three fungi and <it>S. cerevisiae </it>used in the test. Detailed analysis on 30 selected isolates from an orchard at Chanthaburi using the comparison of 16S rRNA gene sequences revealed that most of the isolates (87%) belong to the genus <it>Streptomyces </it>sp., while one each belongs to <it>Saccharopolyspora </it>(strain SB-2) and <it>Nocardiopsis </it>(strain CM-2) and two to <it>Nocardia </it>(strains BP-3 and LK-1). Strains LC-1, LC-4, JF-1, SC-1 and MG-1 exerted high inhibitory activity against all three anthracnose fungi and yeast. In addition, the organic solvent extracts prepared from these five strains inhibited conidial growth of the three indicator fungi. Preliminary analysis of crude extracts by high performance liquid chromatography (HPLC) indicated that the sample from strain JF-1 may contain a novel compound. Phylogenetic analysis revealed that this strain is closely related to <it>Streptomyces cavurensis </it>NRRL 2740 with 99.8% DNA homology of 16S rRNA gene (500 bp).</p> <p>Conclusion</p> <p>The present study suggests that rhizospheric soil is an attractive source for the discovery of a large number of actinomycetes with activity against <it>Colletotrichum </it>spp. An interesting strain (JF-1) with high inhibitory activity has the potential to produce a new compound that may be useful in the control of <it>Colletotrichum </it>spp.</p

Drosophila Lipophorin Receptors Mediate the Uptake of Neutral Lipids in Oocytes and Imaginal Disc Cells by an Endocytosis-Independent Mechanism

Lipids are constantly shuttled through the body to redistribute energy and metabolites between sites of absorption, storage, and catabolism in a complex homeostatic equilibrium. In Drosophila, lipids are transported through the hemolymph in the form of lipoprotein particles, known as lipophorins. The mechanisms by which cells interact with circulating lipophorins and acquire their lipidic cargo are poorly understood. We have found that lipophorin receptor 1 and 2 (lpr1 and lpr2), two partially redundant genes belonging to the Low Density Lipoprotein Receptor (LDLR) family, are essential for the efficient uptake and accumulation of neutral lipids by oocytes and cells of the imaginal discs. Females lacking the lpr2 gene lay eggs with low lipid content and have reduced fertility, revealing a central role for lpr2 in mediating Drosophila vitellogenesis. lpr1 and lpr2 are transcribed into multiple isoforms. Interestingly, only a subset of these isoforms containing a particular LDLR type A module mediate neutral lipid uptake. Expression of these isoforms induces the extracellular stabilization of lipophorins. Furthermore, our data indicate that endocytosis of the lipophorin receptors is not required to mediate the uptake of neutral lipids. These findings suggest a model where lipophorin receptors promote the extracellular lipolysis of lipophorins. This model is reminiscent of the lipolytic processing of triglyceride-rich lipoproteins that occurs at the mammalian capillary endothelium, suggesting an ancient role for LDLR–like proteins in this process

Molecular mechanisms of EGF signaling-dependent regulation of pipe, a gene crucial for dorsoventral axis formation in Drosophila

During Drosophila oogenesis the expression of the sulfotransferase Pipe in ventral follicle cells is crucial for dorsoventral axis formation. Pipe modifies proteins that are incorporated in the ventral eggshell and activate Toll signaling which in turn initiates embryonic dorsoventral patterning. Ventral pipe expression is the result of an oocyte-derived EGF signal which down-regulates pipe in dorsal follicle cells. The analysis of mutant follicle cell clones reveals that none of the transcription factors known to act downstream of EGF signaling in Drosophila is required or sufficient for pipe regulation. However, the pipe cis-regulatory region harbors a 31-bp element which is essential for pipe repression, and ovarian extracts contain a protein that binds this element. Thus, EGF signaling does not act by down-regulating an activator of pipe as previously suggested but rather by activating a repressor. Surprisingly, this repressor acts independent of the common co-repressors Groucho or CtBP

Cad74A is regulated by BR and is required for robust dorsal appendage formation in Drosophila oogenesis

Drosophila egg development is an established model for studying epithelial patterning and morphogenesis, but the connection between signaling pathways and egg morphology is still incompletely understood. We have identified a non-classical cadherin, Cad74A, as a putative adhesion gene that bridges epithelial patterning and morphogenesis in the follicle cells. Starting in mid-oogenesis, Cad74A is expressed in the follicle cells that contact the oocyte, including the border cells and most of the columnar follicle cells. However, Cad74A is repressed in two dorsolateral patches of follicle cells, which participate in the formation of tubular respiratory appendages. We show genetically that Cad74A is downstream of the EGFR and BMP signaling pathways and is repressed by the Zn-finger transcription factor Broad. The correlation of Cad74A repression in the cells that bend out of the plane of the follicular epithelium is preserved across Drosophila species and mutant backgrounds exhibiting a range of eggshell phenotypes. Complete removal of Cad74A from the follicle cells causes defects in dorsal appendage formation. Ectopic expression of Cad74A in the roof cells results in shortened, flattened appendages due to the hindered migration of the roof cells. Based on these results, we propose that Cad74A is part of the adhesive machinery that enables robust dorsal appendage formation, and as such provides a link between the patterning of the follicle cells and eggshell morphogenesis

Expression patterns of cadherin genes in Drosophila oogenesis

In Drosophila oogenesis, the follicular epithelium that envelops the oocyte is patterned by a small set of inductive signals and gives rise to an elaborate three-dimensional eggshell. Several eggshell structures provide sensitive readouts of the patterning signals, but the formation of these structures is still poorly understood. In other systems, epithelial morphogenesis is guided by the spatial patterning of cell adhesion and cytoskeleton genes. As a step towards developing a comprehensive description of patterning events leading to eggshell morphogenesis, we report the expression of Drosophila cadherins, calcium-dependent adhesion molecules that are repeatedly used throughout development. We found that 9/17 of Drosophila cadherins are expressed in the follicular epithelium in dynamic patterns during oogenesis. In late oogenesis, the expression patterns of cadherin genes in the main body follicle cells is summarized using a compact set of simple geometric shapes, reflecting the integration of the EGFR and DPP inductive signals. The multi-layered composite patterning of the cadherins is hypothesized to play a key role in the formation of the eggshell. Of particular note is the complex patterning of the region of the follicular epithelium that gives rise to the dorsal appendages, which are tubular structures that serve as respiratory organs for the developing embryo

Pattern formation by dynamically interacting network motifs

Systematic validation of pattern formation mechanisms revealed by molecular studies of development is essentially impossible without mathematical models. Models can provide a compact summary of a large number of experiments that led to mechanism formulation and guide future studies of pattern formation. Here, we realize this program by analyzing a mathematical model of epithelial patterning by the highly conserved EGFR and BMP signaling pathways in Drosophila oogenesis. The model accounts for the dynamic interaction of the feedforward and feedback network motifs that control the expression of Broad, a zinc finger transcription factor expressed in the cells that form the upper part of the respiratory eggshell appendages. Based on the combination of computational analysis and genetic experiments, we show that the model accounts for the key features of wild-type pattern formation, correctly predicts patterning defects in multiple mutants, and guides the identification of additional regulatory links in a complex pattern formation mechanism