Biomedical subjects

G M Rubin

Publications and source records attributed to G M Rubin.

At least 127 records · Page 7Linked to original sources

PubMed1992

Mutations on the second chromosome affecting the Drosophila eye.

In the developing eye of Drosophila, cell interactions appear to be responsible for organising undifferentiated cells into unit eyes, or ommatidia. Extensive mutagenesis has been used to search for mutations affecting the development and differentiation of ommatidia. These mutations have been characterized using sections of adults and immunocytochemistry of imaginal discs. Fourteen loci on the second chromosome are described that affect the spacing of the preclusters, the differentiation of ommatidial cells, orientation of the ommatidia, or architecture of the adult retina, that cause retinal degeneration in larval or pupal eye discs, or that cause homeotic transformation of part of the head.

Animals↗

PubMed1992

Ectopic expression of ultraviolet-rhodopsins in the blue photoreceptor cells of Drosophila: visual physiology and photochemistry of transgenic animals.

We have generated transgenic flies expressing R7 cell-specific opsins in the major class of photoreceptor cells of the Drosophila retina and characterized their spectral properties using high-resolution microspectrophotometry and sensitivity recordings. We show that the Rh3 and Rh4 opsin genes encode UV-sensitive opsins with similar spectral properties (lambda max = 345 nm and 375 nm), and that Rh3 corresponds to the R7p and R7marg class of visual pigments. We have also generated Rh3 and Rh4 isoform-specific antibodies and present an R7 cell map of the Drosophila retina. In a related set of experiments, we show that it is possible to coexpress two different visual pigments functionally in the same cell and produce photoreceptors that display the summed spectral response of the individual pigments. These findings open up the possibility of tuning an animal's visual behavior by targeted expression of combinations of opsin genes to selective types of photoreceptors.

Animals↗

PubMed1991

Cloning and characterization of a receptor-class phosphotyrosine phosphatase gene expressed on central nervous system axons in Drosophila melanogaster.

We have cloned and characterized cDNAs coding for a receptor-class phosphotyrosine phosphatase gene from Drosophila melanogaster. The gene maps to the polytene chromosome bands 99A7-8. The cDNA clones code for a polypeptide of 1301 amino acids with a predicted molecular mass of 145 kDa. The extracellular domain includes two fibronectin-type III-like domains. The cytoplasmic region contains two tandemly repeated phosphotyrosine phosphatase-like domains. Residues shown crucial for catalytic activity are absent in the second domain. This Drosophila receptor-class phosphotyrosine phosphatase polypeptide is expressed on axons of the embryonic central nervous system.

Amino Acid Sequence↗

PubMed1991

Ras1 and a putative guanine nucleotide exchange factor perform crucial steps in signaling by the sevenless protein tyrosine kinase.

We have conducted a genetic screen for mutations that decrease the effectiveness of signaling by a protein tyrosine kinase, the product of the Drosophila melanogaster sevenless gene. These mutations define seven genes whose wild-type products may be required for signaling by sevenless. Four of the seven genes also appear to be essential for signaling by a second protein tyrosine kinase, the product of the Ellipse gene. The putative products of two of these seven genes have been identified. One encodes a ras protein. The other locus encodes a protein that is homologous to the S. cerevisiae CDC25 protein, an activator of guanine nucleotide exchange by ras proteins. These results suggest that the stimulation of ras protein activity is a key element in the signaling by sevenless and Ellipse and that this stimulation may be achieved by activating the exchange of GTP for bound GDP by the ras protein.

Amino Acid Sequence↗

PubMed1991

The Drosophila roughened mutation: activation of a rap homolog disrupts eye development and interferes with cell determination.

Roughened is a dominant mutation of D. melanogaster that disrupts eye development. The majority of the ommatidia in the adult eye lack a single photoreceptor cell, which is most commonly the R7 cell. The Roughened mutation disrupts the early stages of photoreceptor cell determination. Roughened is a dominant gain-of-function mutation that results from a single amino acid change (Phe157 to Leu) in the Drosophila Rap1 protein. Loss of function Rap1 mutations are lethal. Drosophila Rap1 protein is 88% identical to human rap1A/K-rev1 protein, a putative antagonist of ras action.

Amino Acid Sequence↗

PubMed1991

Evolution of gene position: chromosomal arrangement and sequence comparison of the Drosophila melanogaster and Drosophila virilis sina and Rh4 genes.

The seven in absentia (sina) gene of Drosophila encodes a nuclear protein required for normal eye development. In Drosophila melanogaster, the sina gene is located within an intron of the Rh4 opsin gene. We examine here the nucleotide sequences and chromosomal arrangements of these genes in Drosophila virilis. An interspecies comparison between D. melanogaster and D. virilis reveals that the protein-coding sequences of the sina and Rh4 genes are highly conserved, but the relative chromosomal position and structural arrangement of these genes differ between the two species. In particular, the sina and Rh4 genes are widely separated in D. virilis, and there is no intron in the Rh4 gene. Our results suggest that the Rh4 gene was translocated to another chromosomal location by a retrotransposition event.

Animals↗

PubMed1991

Isolation of temperature-sensitive mutations of the tyrosine kinase receptor sevenless (sev) in Drosophila and their use in determining its time of action.

Loss-of-function mutations in the sevenless (sev) gene in Drosophila result in the failure to differentiate a specific photoreceptor cell type--namely, the R7 cell. The sev gene encodes a cell-surface receptor tyrosine kinase that functions in the presumptive R7 cell to transduce developmental cues from its neighbors, instructing it to differentiate along the R7 cell pathway. We have isolated temperature-sensitive alleles of sev and used them to show that Sev activity is required for several hours during the development of each R7 cell to specify R7 cell differentiation. Our data also suggest that the presumptive R7 cell remains for approximately 5 hr in an undetermined state in the absence of the Sev-mediated signal before committing to an alternative fate. We have determined the molecular lesions in four of the temperature-sensitive alleles. One of these mutations disrupts the Gly-Xaa-Gly-Xaa-Xaa-Gly consensus in the ATP-binding site of the kinase domain.

Alleles↗

PubMed1991

Analysis of the enhancer element that controls expression of sevenless in the developing Drosophila eye.

The sevenless gene encodes a protein-tyrosine kinase receptor expressed in a complex pattern during the development of the Drosophila melanogaster eye. We have previously shown that this pattern is regulated transcriptionally by an enhancer located in the body of the sevenless gene. Here we extend our analysis of the sevenless enhancer, defining a 475-base-pair fragment that contains elements necessary for the correct qualitative and quantitative expression of the sevenless gene. Within this fragment are sequence elements conserved in the sevenless gene of a distantly related Drosophila species and protected from DNase I digestion by nuclear extracts isolated from adult heads and imaginal discs. Partial deletions of the 475-base-pair fragment result in preferential loss of expression in different subsets of cells. These results suggest that the normal pattern of expression is generated by the combined action of separate cell-specific regulatory elements.

Animals↗

PubMed1991

Isolation and characterization of the disconnected gene of Drosophila melanogaster.

Mutations in the disco (disconnected) gene prevent the establishment of stable connections between the larval optic nerves, the Bolwig's nerves, and their target cells in the brain during embryonic development. The failure of this initial connection is associated with aberrant development of the optic lobes which are largely degenerate in the mutant adult fly. In order to understand the role of disco in establishing this connection, we isolated and characterized the disco gene. A 22 kb DNA fragment can completely rescue the mutant phenotype. A single transcript, 2.9 kb in length, is found in this region and is expressed throughout development of the fly. We determined the nucleotide sequence of the disco gene to be unique when compared with sequences in a number of databases. The predicted amino acid sequence contains a region with similarity to the consensus established for the zinc finger motif. Mobilization of a P-element inserted near the gene resulted in the deletion of the 5' end of the gene and produced flies indistinguishable from those carrying the disco allele.

Amino Acid Sequence↗

PubMed1991

The optic lobe projection pattern of polarization-sensitive photoreceptor cells in Drosophila melanogaster.

Histological staining of wild-type and sevenless transgenic Drosophila melanogaster bearing Rh3-lacZ fusion genes permits the selective visualization of polarization-sensitive R7 and R8 photoreceptor cells located along the dorsal anterior eye margin. Diffusion of beta-galactosidase throughout these cells reveals that they project long axons to the two most peripheral synaptic target rows of the dorsal posterior medulla, defining a specialized marginal zone of this optic lobe. Comparison of the staining patterns of marginal and nonmarginal Rh3-lacZ-expressing photoreceptor cells in the same histological preparations suggest that the marginal cells possess morphologically specialized axons and synaptic terminals. These findings are discussed with reference to the neuroanatomy of the corresponding dorsal marginal eye and optic lobe regions of the larger dipterans Musca and Calliphora, and in relation to the ability of Drosophila to orient to polarized light.

Animals↗

PubMed1991

Clinical pharmacology of intravenous enoximone: pharmacodynamics and pharmacokinetics in patients with heart failure.

Twenty-one patients with heart failure (New York Heart Association [NYHA] class II to IV) received a 24-hour infusion of enoximone followed by a 12-hour washout period. Patients were randomly assigned to one of four treatment groups. Groups I to III received an 0.5 mg/kg bolus, followed by a maintenance infusion of 2.5, 5.0, or 10.0 micrograms/kg/min. Group IV patients received a maintenance infusion of 5.0 micrograms/kg/min without a loading dose. Serial assessment of hemodynamics, plasma levels of enoximone and enoximone sulfoxide, and ventricular ectopy were performed. Enoximone produced a clinically significant increase in cardiac index, and a decrease in mean pulmonary artery wedge pressure and systemic vascular resistance in all groups. Enoximone mildly increased heart rate, and had a minimal effect on mean arterial pressure. There was no statistically significant change in ventricular ectopy during the infusion. Significant hemodynamic improvement was noted at even the lowest infusion rate, and did not increase in linear fashion at higher infusion rates. In patients who did not receive an initial loading bolus of 0.5 mg/kg, the increase in cardiac index was delayed by approximately 1 hour. Plasma concentrations of both enoximone and its major metabolite continued to rise throughout the 24-hour infusion in group III (10.0 micrograms/kg/min), rather than reaching steady state as predicted by the terminal exponential half-lives of these compounds. This is suggestive of nonlinear pharmacokinetics and indicates a potential for excessive accumulation of enoximone and its metabolite during prolonged infusion. These findings may have important implications in guiding the intravenous administration of enoximone.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1991

Star is required in a subset of photoreceptor cells in the developing Drosophila retina and displays dosage sensitive interactions with rough.

We report that mutations at the Star locus act as dominant enhancers of the eye phenotype displayed by flies carrying a null allele of rough. Our analysis of double mutants at different stages of eye development suggests that this phenotype results from defects in the early stages of photoreceptor cell differentiation in the eye imaginal disc. Complete loss of Star function during retinal development, analyzed in mosaic animals, results in cell death, visible as scars in the adult eye. The requirement for wild-type Star function, however, is confined to only a subset of photoreceptor cells, R8, R2, and R5, which are the first three cells to differentiate neurally in the developing retina. These results suggest an essential role for the Star gene in the initial events of ommatidial cluster formation during the development of the Drosophila compound eye.

Alleles↗

PubMed1991

The Drosophila zfh-1 and zfh-2 genes encode novel proteins containing both zinc-finger and homeodomain motifs.

Two of the most common DNA-binding motifs found in eukaryotic transcriptional regulatory proteins are the homeodomain and the C2-H2 zinc finger. In Drosophila, homeodomain and zinc-finger proteins have been implicated in a wide variety of developmental processes. Until now, no proteins have been described in which both these DNA-binding motifs are present. We report here the isolation of genes encoding two such Drosophila proteins from a cDNA expression library. The product of the zfh-1 gene (zinc-finger homeodomain protein 1) contains one homeodomain and nine C2-H2 zinc fingers. The product of the zfh-2 gene possesses three homeodomains and sixteen C2-H2 zinc fingers. For zfh-1, antisera raised against nonoverlapping regions of the gene product all recognize a 145 kDa protein on protein immunoblots, suggesting that the different DNA-binding motifs are actually all present in the mature gene product. The novel arrangement of interspersed homeodomain and zinc-finger motifs in the primary sequences of the zfh-1 and zfh-2 gene products may signify an unusual mechanism of transcriptional regulation by these proteins.

Amino Acid Sequence↗

PubMed1991

The embryonic expression patterns of zfh-1 and zfh-2, two Drosophila genes encoding novel zinc-finger homeodomain proteins.

The zfh-1 and zfh-2 genes of D. melanogaster encode novel proteins containing both homeodomain and C2-H2 zinc-finger DNA-binding motifs. Antisera against these proteins were used to investigate their expression patterns during embryonic development. The zfh-1 gene is expressed in the mesoderm of early embryos and in a number of mesodermally-derived structures of late embryos, including the dorsal vessel, support cells of the gonads, and segment-specific arrays of adult muscle precursors. In addition, zfh-1 is expressed in the majority of identified motor neurons of the developing CNS. The mesodermal zfh-1 expression requires the products of the twist and snail genes. The zfh-2 gene displays a more limited expression pattern, largely restricted to the CNS of late embryos. Ubiquitous zfh-1 expression in transgenic flies bearing an hsp70-zfh-1 construct has specific developmental consequences, including embryonic CNS defects as well as adult eye and bristle abnormalities. The expression patterns of zfh-1 and zfh-2 suggest that both genes may be involved in Drosophila neurogenesis and that zfh-1 may have additional functions in mesoderm development.

Animals↗

PubMed1991

Glass encodes a site-specific DNA-binding protein that is regulated in response to positional signals in the developing Drosophila eye.

The glass gene encodes a zinc finger protein required for normal photoreceptor cell development in Drosophila. We show that glass transcripts are present in the third-instar eye-imaginal disc starting in the morphogenetic furrow and extending to the posterior margin of the disc; glass protein is detected in the nuclei of all cells in this region. We also show that glass encodes a site-specific DNA-binding protein. A 27-bp glass-binding site can confer glass-dependent expression on a reporter gene in developing photoreceptor cells, the particular subset of glass-expressing cells known to require glass function. This specificity may represent a regulation of glass protein activity after cells are recruited to the photoreceptor cell fate.

Animals↗

PubMed1991

Cell-fate determination in the developing Drosophila eye: role of the rough gene.

The homeobox-gene rough is required in photoreceptor cells R2 and R5 for normal ommatidial assembly in the developing Drosophila eye. We have used several cell-type-specific markers and double mutant combinations to analyze cell-fate determination in rough. We show that the cells that would normally become R2 and/or R5 express a marker, a lacZ insertion in the seven-up (svp) gene, which is indicative of the R1/3/4/6 cell fate. In addition, the analysis of mitotically induced svp,ro double mutant clones in the eye indicates that in rough all outer photoreceptors are under the genetic control of the svp gene. These results show that, in the absence of rough function, R2 and R5 fail to be correctly determined and appear to be transformed into cells of the R3/4/1/6 subtype. This transformation and the subsequent developmental defects do not preclude the recruitment of R7 cells. However, the presence of ommatidia containing more than one R7 and/or R8 cell in rough implies a complex network of cellular interactions underlying cell-fate determination in the Drosophila retina.

Animals↗

PubMed1990

Spacing differentiation in the developing Drosophila eye: a fibrinogen-related lateral inhibitor encoded by scabrous.

In the development of multicellular organisms a diversity of cell types differentiate at specific positions. Spacing patterns, in which an array of two or more cell types forms from a uniform field of cells, are a common feature of development. Identical precursor cells may adopt different fates because of competition and inhibition between them. Such a pattern in the developing Drosophila eye is the evenly spaced array of R8 cells, around which other cell types are subsequently recruited. Genetic studies suggest that the scabrous mutation disrupts a signal produced by R8 cells that inhibits other cells from also becoming R8 cells. The scabrous locus was cloned, and it appears to encode a secreted protein partly related to the beta and gamma chains of fibrinogen. It is proposed that the sca locus encodes a lateral inhibitor of R8 differentiation. The roles of the Drosophila EGF-receptor homologue (DER) and Notch genes in this process were also investigated.

Alleles↗

PubMed1990

seven in absentia, a gene required for specification of R7 cell fate in the Drosophila eye.

Signals from directly adjacent cells are critical for the development of the R7 photoreceptor cell in the Drosophila eye. We have identified a gene, seven in absentia (sina), for which loss of function results in the R7 precursor cell adopting the fate of a nonneuronal cell type. Function of the sina gene is required only in R7 for correct R7 cell development. The sina transcription unit is located within the intron of a gene that encodes an R7 cell-specific opsin. The sina protein, which has a potential metal binding domain, is localized in the nuclei of several ommatidial precursor cells including R7, and sina expression in R7 appears before R7 overtly begins to differentiate. These data indicate that the sina gene product is necessary at a stage in the determination of R7 cell fate when R7 receives and interprets developmental signals from neighboring cells, and possibly acts by regulating gene expression.

Amino Acid Sequence↗