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D L Brower

Publications and source records attributed to D L Brower.

At least 37 records · Page 2Linked to original sources
PubMed1993

Functional properties of alternatively spliced forms of the Drosophila PS2 integrin alpha subunit.

The Drosophila alpha PS2 protein is encoded by two alternatively spliced transcripts. The respective alpha PS2 proteins differ by the presence of 25 amino acids in the alpha PS2(C) protein, not found in the alpha PS2(m8) subunit, in a region thought to be important for ligand binding. We examined the functional properties of Drosophila S2 cells transformed with genes expressing either of these proteins, in association with a beta PS subunit. Both PS2 integrins support cell spreading on vertebrate vitronectin or, to a lesser extent, on fibronectin. Interestingly, the PS2(C) form promotes spreading more efficiently on vitronectin than does the PS2(m8) form, with an opposite relative efficiency seen for fibronectin. Also, the two forms of PS2 show different requirements for divalent cations in order to mediate efficient cell spreading. These divalent cations are not required to maintain the association of alpha and beta subunits. Spreading of both cell types is similarly RGD sensitive, and both PS2 integrins appear to associate with the actin cytoskeleton. To our knowledge, this represents the first demonstration of functional differences in integrin subunits resulting from splicing variation to generate different extracellular, ligand binding domains.

Alternative Splicing↗
PubMed1992

Evaluation of Drosophila melanogaster as an alternative animal for studying the neurotoxicity of heavy metals.

Heavy metals cause irreversible neurobehavioral damage in many developing mammals, but the mechanisms of this damage are unknown. The influence of three heavy metal compounds, triethyllead chloride, lead acetate and cadmium chloride, on lethality, development, behavior and learning was studied using the fruit fly, Drosophila melanogaster. This animal was used because it allows hundreds of subjects to be assayed very easily in individual experiments and because it is a system in which toxicological questions might be answered by using the techniques of modern molecular genetics. When triethyllead chloride, lead acetate or cadmium chloride was placed in the medium, the larval LC50 (+/- standard error) was found to be 0.090 +/- 0.004, 6.60 +/- 0.64 and 0.42 +/- 0.04 mM, respectively. Each of the tested compounds produced a dose-related delay in development. In particular, they caused a delay in the development of larvae to pupae. When larvae were reared on medium containing triethyllead chloride (0.06 mM), lead acetate (3.07 mM) or cadmium chloride (0.11 mM), phototaxis, locomotion and learning were not inhibited. Since significant neurobehavioral effects were not observed under the experimental conditions used, Drosophila does not appear to be an appropriate animal for the genetic dissection of such effects of heavy metals during development.

Animals↗
PubMed1992

Characterization of mutant alleles of myospheroid, the gene encoding the beta subunit of the Drosophila PS integrins.

This paper presents the characterization of nine alleles of myospheroid, which encodes the beta PS subunit of the Drosophila PS integrins. On Southern blots, the mysXB87, mysXN101 and mysXR04 genes yield restriction digest patterns similar to that seen for wild-type chromosomes, however the mys1 and mysXG43 genes contain detectable deletions. mys1, mysXB87 and mysXG43 make little or no stable protein product, and genetically behave as strong lethal alleles. For the mysXN101 mutation, protein product is seen on immunoblots and a reduced amount of beta PS protein is seen at muscle attachment sites of embryos; this mutant protein retains some wild-type function, as revealed by complementation tests with weak alleles. Protein is also seen on immunoblots from mysXR04 embryos, and this allele behaves as an antimorph, being more deleterious in some crosses than the complete deficiency for the locus. mysts2 and mysnj42 are typically lethal in various combinations with other alleles at high temperatures only, but even at high physiological temperatures, neither appears to eliminate gene function completely. The complementation behaviors of mysts1 and mysts3 are quite unusual and suggest that these mutations involve regulatory phenomena. For mysts3, the data are most easily explained by postulating transvection effects at the locus. The results for mysts1 are less straightforward, but point to the possibility of a chromosome pairing-dependent negative interaction.

Alleles↗
PubMed1992

Drosophila PS2 integrin mediates RGD-dependent cell-matrix interactions.

Integrins are a family of transmembrane glycoproteins that mediate cell-matrix and cell-cell interactions. We have transfected cultured Drosophila cells with genes that express the Drosophila PS2 integrin. We demonstrate that this integrin is expressed on the surface of the cells and can mediate cell spreading on an undefined component of fetal calf serum or on the purified vertebrate matrix molecules vitronectin and fibronectin. Additionally, PS2 integrin can cause cell spreading on RGD peptide. The spreading on matrix components or RGD peptide can be inhibited by soluble RGD peptide and is dependent on divalent cations.

Animals↗
PubMed1990

Persistent ectopic expression of Drosophila homeotic genes resulting from maternal deficiency of the extra sex combs gene product.

Like other members of the Polycomb group, the extra sex combs gene (esc) is required for the correct repression of loci in the major homeotic gene complexes. We show here that embryos lacking both maternal and zygotic esc+ function display transient, general derepression of both the Ultrabithorax (Ubx) and Antennapedia (Antp) genes during germ band shortening, but Sex combs reduced (Scr) expression is almost normal in the epidermis and lacking in the central nervous system (CNS). In addition, embryos that are maternally esc- but receive two paternal copies of esc+ often are characterized by ectopic expression of the three homeotic genes, especially Ubx and Antp in the CNS. Imaginal discs from these paternally rescued embryos may show discrete patches of expression of Ubx and Scr in inappropriate locations. Thus, lack of esc+ function during a brief period in early embryogenesis results in a heritable change in determined state, even in a genetically wild type animal. Within these ectopic patches, homeotic gene expression may be regulated by the disc positional fields and by cross-regulatory interactions between homeotic genes.

Alleles↗
PubMed1990

Effect of abx, bx and pbx mutations on expression of homeotic genes in Drosophila larvae.

We have examined the patterns of expression of the homeotic gene Ubx in imaginal discs of Drosophila larvae carrying mutations in the abx, bx and pbx regulatory domains. In haltere discs, all five bx insertion mutations examined led to a general reduction in Ubx expression in the anterior compartment; for a given allele, the strength of the adult cuticle phenotype correlated with the degree of Ubx reduction. Deletions mapping near or overlapping the sites of bx insertions, including three abx alleles and the bx34e-prv(bx-prv) allele, showed greatly reduced Ubx expression in parts of the anterior compartment of the haltere disc; however, anterior patches of strong Ubx expression often remained, in highly variable patterns. As expected, the pbx1 mutation led to reduced Ubx expression in the posterior compartment of the haltere disc; surprisingly, pbx1 also led to altered expression of the en protein near the compartment border in the central region of the disc. In the metathoracic leg, all the bx alleles caused extreme reduction in Ubx expression in the anterior regions, with no allele-specific differences. In contrast, abx and bx-prv alleles resulted in patchy anterior reductions in third leg discs. In the larval central nervous system, abx but not bx alleles affected Ubx expression; the bx-prv deletion gave a wild-type phenotype, but it could not fully complement abx mutations. In the posterior wing disc, the bx-prv allele, and to a much lesser extent the bx34e chromosome from which it arose, led to ectopic expression of Ubx. Unlike other grain-of-function mutations in the BX-C, this phenotype appeared to be partially recessive to wild type. Finally, we asked whether the ppx transformation, which results from early lack of Ubx+ function in the mesothorax and is seen in abx animals, is due to ectopic Scr expression. Some mesothoracic leg and wing discs from abx2 larvae displayed ectopic expression of Scr, which was variable in extent but always confined to the posterior compartment.

Alleles↗
PubMed1989

Requirement for integrins during Drosophila wing development.

The position-specific (PS) integrins of Drosophila are highly homologous to vertebrate integrins, most of which are cell-surface receptors for extracellular matrix components. Integrins are heterodimers, each consisting of noncovalently associated alpha- and beta-subunits. As for the subfamilies of vertebrate integrins, the same beta-subunit is found in both Drosophila PS integrins, combined with a specific alpha-subunit to generate either a complete functional PS1 or PS2 integrin. Both alpha- and beta-subunits are large transmembrane proteins (relative molecular masses greater than 100,000). Either one or both of these two PS integrins are expressed in most fly tissues during development. A particularly intriguing pattern of expression is found in the mature wing imaginal disc, where the PS1 integrin is expressed primarily on the presumptive dorsal wing epithelium, and the PS2 integrin is found almost exclusively on the ventral epithelium. Immediately after pupariation, the central wing pouch evaginates, folding along its centre to appose the epithelia that will secret the dorsal and ventral surfaces of the adult wing blade. Here we report the results of a genetic analysis indicating that both of the PS integrins are required to maintain the close apposition of the dorsal and ventral wing epithelia during morphogenesis. Also, we conclude that the integrins are not necessary for the maintenance of the cell lineage restriction between the two presumptive wing surfaces in the developing imaginal disc.

Alleles↗
PubMed1989

Allelic interactions at the engrailed locus of Drosophila: engrailed protein expression in imaginal discs.

Many embryonic lethal engrailed (enlethal) mutations are known to partially complement the cuticular defects of the original engrailed mutation, en1. To explore the nature of this complementation, the adult phenotypes of several different en1/enlethal transheterozygotes were compared with the corresponding patterns of engrailed protein expression in third larval instar imaginal discs (determined by immunofluorescence). Transheterozygotes of en1 and deletions of the locus (enDf) typically show slight complementation in the adult cuticle. The pattern of engrailed protein expression in some en1/enDf wing discs is indistinguishable from en1 homozygotes, but in others the pattern is nearly normal. en1/enDf leg discs appear to express engrailed protein normally. Transheterozygotes of en1 and EMS-induced, cytologically normal enlethal alleles have almost normal adult cuticle phenotypes and also exhibit normal patterns of engrailed protein expression in all of the thoracic imaginal discs. Surprisingly, the intensity of anti-engrailed staining in these discs is elevated relative to that in wild type. en2 is an unusual lethal allele in that it does not complement either the en1 adult cuticle phenotype or the protein expression pattern in imaginal discs. Moreover, the cytologically normal enlethal alleles also complement en2, at least partially. Both wing and leg imaginal discs from en2/enlethal transheterozygotes show abnormal patterns of engrailed protein expression. These results are discussed in the context of an autoregulatory model for engrailed regulation.

Alleles↗
PubMed1988

Misregulation of homeotic gene expression in Drosophila larvae resulting from mutations at the extra sex combs locus.

Using monoclonal antibodies specific for their protein products, the expression of the Ubx, Antp, and Scr genes was examined in imaginal discs and central nervous systems of esc-Drosophila larvae. In esc-mutants, both the Ubx and Scr proteins are expressed at increased levels or in new locations in the leg discs. Ubx also is expressed in new locations in the posterior wing disc and in small groups of cells in the antenna disc. The Antp protein is expressed ectopically in the eye-antenna disc; however, obvious abnormal expression of Antp was not found in the thoracic imaginal discs. Particularly striking is the fact that a single disc, such as the mesothoracic leg, can show increased expression of both a more "anterior" homeotic gene (Scr) and a more "posterior" gene (Ubx). Ectopic expression of Ubx and Antp, but not of Scr, is seen in the central nervous system of mutant larvae. These results are discussed with respect to the adult esc-phenotype and the differential effects of esc mutations on early and late development.

Alleles↗
PubMed1988

Expression of the Sex combs reduced protein in Drosophila larvae.

We have generated a monoclonal antibody that binds specifically to the protein product of the homeotic Sex combs reduced (Scr) gene of Drosophila, and have mapped the patterns of Scr expression in late third instar larvae. Virtually the entire prothoracic leg imaginal disc expresses the gene, although the levels of expression vary in different disc regions. This heterogeneity does not reflect the compartmental domains defined by engrailed gene expression. Expression is also observed in the cells of the humeral and labial discs, and there is a small patch of Scr-expressing cells in the antenna disc. The gene is expressed in adepithelial cells of the three thoracic leg discs, but not in the wing or haltere discs. In the central nervous system, Scr expression is confined to a narrow band of cells in the subesophageal region of the ventral ganglion. The results are discussed with respect to the known genetic requirements for Scr+ function.

Animals↗
PubMed1987

Identification of a specialized extracellular matrix component in Drosophila imaginal discs.

We have generated a monoclonal antibody that recognizes a major component of a specialized extracellular matrix in Drosophila imaginal discs. In mature larvae, antibody binding is observed almost exclusively on imaginal discs. On the basal surface of the thoracic discs, the antigen is localized to particular regions of the epithelium, and ultrastructural studies indicate that the antigen is found in a fibrous network secreted between the cells and the basal lamina. The localized expression indicates that the matrix is not simply related to disc differentiation, as all regions of the columnar disc epithelium are determined to secrete adult cuticle. A correlation of the antigen distribution with known developmental events leads us to propose that the antigen-containing network provides an extensible matrix for the rapid elongation of the disc epithelium during evagination; consistent with this, the antigen is a component of the matrix between the dorsal and ventral surfaces of the evaginated wing pouch. The antigen is very large (greater than 5 X 10(5) Da), can be labeled metabolically with methionine and sulfate, and is digested by chondroitinase ABC; these biochemical characteristics indicate that the antigen is a proteoglycan.

Animals↗
PubMed1987

Segmentally repeated pattern of expression of a cell surface glycoprotein in Drosophila embryos.

We report here that a previously described cell surface antigen (Brower, Smith & Wilcox, 1980) is expressed in a segmentally repeating pattern of stripes in the epidermis and nervous system of segmented Drosophila embryos. We also report that the antigenic activity is found on two closely related cell surface glycoproteins. The pattern of expression of this antigen is reminiscent of the expression of some segmentation genes and is affected by mutation of at least two of these genes, fushi tarazu and paired. Thus these glycoproteins are candidates for cell surface molecules involved in carrying out the patterning processes controlled by segmentation genes.

Animals↗
PubMed1987

Ultrabithorax gene expression in Drosophila imaginal discs and larval nervous system.

Using a monoclonal antibody and image-processing procedures, the patterns of expression of the Ultrabithorax (Ubx) gene product have been characterized in Drosophila larvae. As reported previously, the metathoracic imaginal discs stain most intensely with anti-Ubx, with some mesothoracic and no prothoracic expression detectable. In the metathoracic discs, the greatest modulation in anti-Ubx staining is along the proximodistal axis. Ubx is generally expressed at higher levels in the posterior regions of metathoracic discs, although relatively high anterior expression is found in some areas. Expression in the mature wing disc is confined to the squamous peripodial membrane cells; in younger wings, Ubx expression fills the posterior half of the peripodial side of the disc. The mesothoracic leg stains with a pattern that is qualitatively similar (but not identical) to that of the metathoracic leg; Ubx is expressed in some anterior regions of the mesothoracic leg, in parasegment 4. Double staining with anti-Ubx and anti-engrailed reveals that discontinuities in Ubx expression that have been suggested to correspond to compartment borders do not coincide with the compartment boundaries in some cases. In the larval ventral ganglion, Ubx expression is greatest in parasegments 5 and 6, as in the embryonic nervous system.

Animals↗
PubMed1986

Engrailed gene expression in Drosophila imaginal discs.

Genetic and molecular analyses indicate that the Drosophila engrailed gene is required to distinguish posterior from anterior compartments in each segment of the developing animal. Here, the patterns of engrailed expression in the imaginal discs and ventral ganglion of Drosophila larvae are examined, using an antiserum against the engrailed protein and a novel image processing method to reduce non-specific background. As expected, engrailed expression generally is restricted to cells in the posterior compartment of the discs, and the patterns of expression allow refinements in the fate maps of the discs to be made. More significant is the finding that expression of the gene is highly variable in different regions of posterior compartments, suggesting that engrailed may do more than simply specify 'posteriorness'. In the ventral ganglion engrailed appears to be expressed by a subset of cells, primarily in the posterior regions of each segment. In wing discs from animals that are homozygous for the en1 mutation, the pattern of expression of the gene is altered, as opposed to being simply reduced uniformly in the posterior cells.

Animals↗
PubMed1986

Disruption of positional fields in apterous imaginal discs of Drosophila.

Certain combinations of alleles at the apterous locus generate wings with extra copies of wing margin structures, some of which are located far from the normal margin. We have examined wing imaginal discs from these mutants, using position-specific antibodies as probes for two-dimensional patterning in the discs. Our results indicate that the adult phenotypes arise from unprecedented disruptions in the two-dimensional pattern of the disc epithelia. Examination of other apterous mutants suggest that pattern alterations may be a general consequence of lesions at this locus.

Animals↗
PubMed1985

Developmental analysis of Drosophila position-specific antigens.

The distributions of three position-specific (PS) antigens have been examined in different Drosophila tissues and at various developmental times, using both immunofluorescence and affinity purification procedures. In the imaginal discs the PS antigens show nonuniform and nonhomologous distributions, and the expression of the antigens in a particular disc region can vary during development. In general, PS antigen expression appears to correlate with morphogenetic events in the disc epithelia, suggesting that the antigens are involved in cell-cell recognition and/or adhesion processes. PS antigens are also found in many other tissues, and in embryos as early as the cellular blastoderm stage. Affinity-purified PS antigens from different tissues or stages appear to be similar, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results are discussed in relation to Drosophila developmental events, with particular regard to the dorsoventral cell lineage restriction in the wing disc.

Animals↗
PubMed1984

Related cell-surface antigens expressed with positional specificity in Drosophila imaginal discs.

We have isolated three classes of monoclonal antibodies against Drosophila cell-surface antigens that are expressed with positional specificity in imaginal discs. Comparison of immunofluorescence patterns with the wing-disc fate map reveals that expression of the antigens is not directly related to the specific type of cuticular structure that a cell will make upon differentiation but depends on the position of the cell in the undifferentiated disc epithelium. On mature wing discs, each class of position-specific (PS) antibody binds nonuniformly with respect to the dorso-ventral compartment boundary, with PS1 antibodies binding primarily to dorsal cells and PS2 antibodies, to ventral cells. Antibodies of the different PS classes extract similar but nonidentical sets of large glycoproteins from cell lysates, and antibodies of the most general class, PS3, recognize the PS1 and PS2 antigens in addition to PS3-specific components. Thus, the distributions and molecular characteristics of the PS antigens suggest that the molecules are structurally and functionally related to one another.

Animals↗