Screening for Drosophila proteins with distinct expression patterns during development by use of monoclonal antibodies

Exploiting Drosophila melanogaster Wing Imaginal Disc Eversion to Screen for New EMT Effectors

In the early stages of Drosophila melanogaster (Drosophila) metamorphosis, a partial epithelial-mesenchymal transition (pEMT) takes place in the peripodial epithelium of wing imaginal discs. Blocking this pEMT results in adults with internalized wings and missing thoracic tissue. Using peripodial GAL4 drivers, GAL80^ts temporal control, and UAS RNAi transgenes, one can use these phenotypes to screen for genes involved in the pEMT. Dominant modifier tests can then be employed to identify genetic enhancers and suppressors. To analyze a gene's role in the pEMT, one can then visualize peripodial cells in vivo at the time of eversion within the pupal case using live markers, and by dissecting, fixing, and immunostaining the prepupae. Alternatively, one can analyze the pEMT ex vivo by dissecting out wing discs and culturing them in the presence of ecdysone to induce eversion. This can provide a clearer view of the cellular processes involved and permit drug treatments to be easily applied.

Serpent/dGATAb regulates Laminin B1 and Laminin B2 expression during Drosophila embryogenesis

Transcriptional regulation of Laminin expression during embryogenesis is a key step required for proper ECM assembly. We show, that in Drosophila the Laminin B1 and Laminin B2 genes share expression patterns in mesodermal cells as well as in endodermal and ectodermal gut primordia, yolk and amnioserosa. In the absence of the GATA transcription factor Serpent, the spatial extend of Laminin reporter gene expression was strongly limited, indicating that Laminin expression in many tissues depends on Serpent activity. We demonstrate a direct binding of Serpent to the intronic enhancers of Laminin B1 and Laminin B2. In addition, ectopically expressed Serpent activated enhancer elements of Laminin B1 and Laminin B2. Our results reveal Serpent as an important regulator of Laminin expression across tissues.

Drosophila hemolectin gene is expressed in embryonic and larval hemocytes and its knock down causes bleeding defects

We have previously identified and characterized Drosophila hemolectin (Hml) in the conditioned medium of a Drosophila cell line. The deduced amino acids sequence contains a number of domains conserved in human von Willebrand factor, coagulation factor V/VIII, and complement factors. To characterize Hml localization and function, we have established two transgenic lines (hml-GAL4 and UAS-hmlRNAi). By crossing hml-GAL4 with UAS-eGFP, we observed that Hml is specifically expressed in embryonic and in larval hemocytes. We determined that Hml is expressed in a subpopulation of plasmatocytes and crystal cells but not in lamellocytes. hml RNAi larvae are viable and do not display obvious developmental defects under normal conditions. However, they show a bleeding defect upon injury. We confirmed that the failure to seal a wound is not due to a defect in melanin production or in phenoloxidase activity. The expression of antimicrobial peptides was not significantly affected on hml RNAi adults. Altogether, our data strongly suggest that Hml is involved in hemostasis and/or coagulation in Drosophila larvae.

Migrating mesoderm establish a uniform distribution of laminin in the developing grasshopper embryo

The basal lamina is composed of molecules which physically interact to form a network that serves as a migrational scaffold for many cell types. In the developing peripheral nervous system of the grasshopper, neuronal growth cones are intimately associated with the basal lamina as they migrate. Laminin is a major component of the basal lamina and is a potent promoter of neurite outgrowth in vitro. However, it is unclear what the source of laminin is or how the distribution of laminin within the basal lamina is established. To address this question, grasshopper laminin subunit genes were cloned. As expected, laminin was found within the basal lamina throughout the embryo, in particular in the limb bud, where its expression is coincident with the outgrowth and guidance of the Tibial (Til) pioneer neurons. Surprisingly, the synthesis of beta and gamma chains of laminin was restricted to migratory mesodermal cells, while in other nonmigratory tissues, such as epithelium and presumptive muscle, beta and gamma chains of laminin were not detected. In spite of this, laminin immunoreactivity in the basal lamina appears uniform and is available as a substrate for axonal outgrowth.

A Drosophila haemocyte-specific protein, hemolectin, similar to human von Willebrand factor

We identified a novel Drosophila protein of approximately 400 kDa, hemolectin (d-Hml), secreted from haemocyte-derived Kc167 cells. Its 11.7 kbp cDNA contains an open reading frame of 3843 amino acid residues, with conserved domains in von Willebrand factor (VWF), coagulation factor V/VIII and complement factors. The d-hml gene is located on the third chromosome (position 70C1-5) and consists of 26 exons. The major part of d-Hml consists of well-known motifs with the organization: CP1-EG1-CP2-EG2-CP3-VD1-VD2-VD'-VD3-VC1-VD"-VD"'-FC1-FC2-VC2-LA1-VD4-VD5-VC3-VB1-VB2-VC4-VC5-CK1 (CP, complement-control protein domain; EG, epidermal-growth-factor-like domain; VB, VC, VD, VWF type B-, C- and D-like domains; VD', VD", VD"', truncated C-terminal VDs; FC, coagulation factor V/VIII type C domain; LA, low-density-lipoprotein-receptor class A domain; CK, cysteine knot domain). The organization of VD1-VD2-VD'-VD3, essential for VWF to be processed by furin, to bind to coagulation factor VIII and to form interchain disulphide linkages, is conserved. The 400 kDa form of d-Hml was sensitive to acidic cleavage near the boundary between VD2 and VD', where the cleavage site of pro-VWF is located. Agarose-gel electrophoresis of metabolically radiolabelled d-Hml suggested that it is secreted from Kc167 cells mainly as dimers. Resembling VWF, 7.9% (305 residues) of cysteine residues on the d-Hml sequence had well-conserved positions in each motif. Coinciding with the development of phagocytic haemocytes, d-hml transcript was detected in late embryos and larvae. Its low-level expression in adult flies was induced by injury at any position on the body.