Myoblast diversification and ectodermal signaling in Drosophila.

The flight muscles of Drosophila derive from myoblasts found on the third instar disc. We demonstrate that these myoblasts already show distinctive properties and examine how this diversity is generated. In the late larva, Vestigial and low levels of Cut are expressed in myoblasts that will contribute to the indirect flight muscles. Other myoblasts, which express high levels of Cut but no Vestigial, are required for the formation of the direct flight muscles. Vestigial and Cut expression are stabilized by a mutually repressive feedback loop. Vestigial expression begins in the embryo in a subset of adult myoblasts, and Wingless signaling is required later to maintain this expression. Thus, myoblasts are divided into identifiable populations, consistent with their allocation to different muscles, and ectodermal signals act to maintain these differences.     

A large family of divergent Drosophila odorant-binding proteins expressed in gustatory and olfactory sensilla.

We identified a large family of putative odorant-binding protein (OBP) genes in the genome of Drosophila melanogaster. Some of these genes are present in large clusters in the genome. Most members are expressed in various taste organs, including gustatory sensilla in the labellum, the pharyngeal labral sense organ, dorsal and ventral cibarial organs, as well as taste bristles located on the wings and tarsi. Some of the gustatory OBPs are expressed exclusively in taste organs, but most are expressed in both olfactory and gustatory sensilla. Multiple binding proteins can be coexpressed in the same gustatory sensillum. Cells in the tarsi that express OBPs are required for normal chemosensation mediated through the leg, as ablation of these cells dramatically reduces the sensitivity of the proboscis extension reflex to sucrose. Finally, we show that OBP genes expressed in the pharyngeal taste sensilla are still expressed in the poxneuro genetic background while OBPs expressed in the labellum are not. These findings support a broad role for members of the OBP family in gustation and olfaction and suggest that poxneuro is required for cell fate determination of labellar but not pharyngeal taste organs.     

Homology of Drosophila yolk proteins and the triacylglycerol lipase family

Drosophila yolk proteins consist of a set of related proteins of 50,000 Mr. They are derived from slightly larger precursors by cleavage of a signal peptide. In this respect, they differ from the yolk proteins of other insects which are proteolytic fragments of precursors of 200,000 Mr or larger, termed vitellogenins and probably homologous to the vitellogenins of other egg-laying species. We report here a comparative amino acid analysis demonstrating that the Drosophila yolk proteins are non-homologous to the vitellogenin group of yolk proteins, but surprisingly are related to the triacylglycerol lipase family.     

The role of Rho family proteins in controlling the migration of crawling cells

Migration of crawling cells (amoebae and some kinds of the tissue cells) is a process related to the dynamic reorganization of actomyosin cytoskeleton. That reorganization engages actin polymerization and de-polymerization, branching of actin network and interaction of myosin II with actin filaments. All those cytoskeleton changes lead to the cell progression, contraction and shifting of the uropod and the cell adhesion. Numerous external stimuli, which activate various surface receptors and signal transduction pathways, can promote migration. Rho family proteins play an important role in the regulation of actin cytoskeleton organization. The most known members of this family are Rho, Rac and Cdc42 proteins, present in all mammalian tissue cells. These proteins control three different stages of cell migration: progression of the frontal edge, adhesion which stabilizes the frontal area, and de-adhesion and shifting of the uropod. Cdc42 and Rac control cell polarization, lamellipodium formation and expansion, organization of focal complexes. Rho protein regulates contractile activity of actomyosin cytoskeleton outside the frontal area, and thus contraction and de-adhesion of the uropod.     

Expression of laminin and of a laminin-related antigen during early development of Drosophila melanogaster

This paper reports the characterization of two immunologically related proteins that may be involved in cell adhesion during Drosophila development. These proteins, laminin chain A and a 240K component, share the epitope recognized by monoclonal antibody RD3 (Mab RD3). The two antigens show different developmental expression profiles. Laminin is detected only from 6 to 8 h of development onwards; its concentration increases during embryogenesis to reach steady-state value in larvae, pupae and adult flies. By contrast, the 240K antigen, not found in oocytes, is present before blastoderm stages; its concentration increases during gastrulation, decreases at the end of organogenesis and the antigen is no longer detected in third instar larvae. Light and electron microscope immunolocalization in imaginal discs indicates that laminin is distributed apically in the lumen and basally in the basal membrane that surrounds the nonevaginated disc. During morphogenesis laminin is detected at the basal side of the evaginating part of the disc epithelium. Immunolocalization on paraffin sections of early embryos suggests that the 240K antigen is related to (1) cell formation and polarization in association with cytoskeleton components, (2) establishment of cell-extracellular substratum interactions during the blastoderm cell sheet organization and (3) basement membrane deposition during embryonic germ cell layer segregation. This 240K protein is poorly or not glycosylated, is resistant to chondroitinase ABC and collagenase and appears therefore as a new extracellular component that might be specifically involved in early processes of morphogenesis.     

A new family of plant antifungal proteins.

Plant seeds contain high concentrations of many antimicrobial proteins. These include chitinases, beta-1,3-glucanases, proteinase inhibitors, and ribosome-inactivating proteins. We recently reported the presence in corn seeds of zeamatin, a protein that has potent activity against a variety of fungi but has none of the above activities. Zeamatin is a 22-kDa protein that acts by causing membrane permeabilization Using a novel bioautography technique, we found similar antifungal proteins in the seeds of 6 of 12 plants examined. A polyclonal antiserum was raised against zeamatin and was used in immunoblots to confirm the presence of zeamatinlike proteins in these seeds. N-terminal amino acid sequencing was carried out on the antifungal proteins from corn, oats, sorghum, and wheat, and these sequences revealed considerable homology with each other. Interestingly, these N-terminal sequences are also similar to those of thaumatin, a pathogenesis-related protein from tobacco, and two salt stress-induced proteins. These results indicate that zeamatin is not unique but is a member of a previously unrecognized family of plant defense proteins that may include some species of pathogenesis-related proteins.     

TGF-beta family factors in Drosophila morphogenesis.

Many Drosophila genes have now been identified with substantial sequence similarity to vertebrate protooncogenes and growth factors. Some of these have been isolated directly by cross-hybridization with vertebrate probes and some have been recognized in the sequences of genes cloned because of their intiguing mutant phenotypes. An example of a gene isolated for its interesting development functions but with homology to a vertebrate growth factor is the Drosophila decapentaplegic gene (dpp). An example of a Drosophila gene isolated by virtue of its sequence conservation is the vgr/60A gene. Both dpp and vgr/60A are members of the transforming growth factor-beta family and are most similar to the human bone morphogenetic proteins. The regulation of the dpp gene by several different groups of pattern formation genes including the dorsal/ventral group, the terminal group, the segment polarity genes, and the homeotic genes indicates that many events in embryogenesis require the cell to cell communication mediated by the secreted dpp protein. The temporal and spatial pattern of vgr/60A expression differs from that of dpp indicating that it may be regulated by different pattern information genes. The experimental advantages of the Drosophila system should permit a better understanding of the importance of growth factor homologs in specific developmental events, aid in establishing the functional interactions between these regulatory molecules, and identify new genes that are important for the biological functions of growth factors. It is likely that some of the newly identified genes will have vertebrate homologs and the analysis of these may be helpful in studies on vertebrate development and tumor biology.     

Cell surface proteins of Drosophila. II. A comparison of embryonic and ecdysone-induced proteins

The cell-surface proteins of Drosophila embryos at gastrula and myoblast fusion stages were characterized by radioiodination and two-dimensional gel electrophoresis. Over 13% of the cell surface proteins detected in gastrula embryos were not found in myoblast fusion stage embryos or in Drosophila embryonic cell line EH34A3 cells. Nearly 18% of the cell-surface proteins detected in myoblast fusion stage embryos were evident only at that stage. Embryonic cell-surface proteins were compared with cell-surface proteins from untreated EH34A3 cells and EH34A3 cells treated with 20-hydroxyecdysone, which induces cell aggregation and the expression of "new" proteins at the cell surface (D. F. Woods and C. A. Poodry, 1983, Dev. Biol. 96, 23-31). Only one of the proteins induced by ecdysone in EH34A3 cells was detected in the NP-40 soluble fraction of radioiodinated cell lysates, even after fractionation by lectin affinity chromatography and immunoprecipitation to enrich for putative ecdysone induced proteins. However, extraction of the NP-40 insoluble pellet of embryo cells revealed one additional protein that was present both in myoblast fusion stage embryos and hormone-treated culture cells. It was concluded that except for these two proteins, the cell-surface proteins induced in cultured cell lines by treatment with 20-hydroxyecdysone are not present in significant amounts in gastrula or myoblast fusion stage embryos.