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G M Rubin

Publications and source records attributed to G M Rubin.

At least 73 records · Page 4Linked to original sources
PubMed1996

A Drosophila gene regulated by rough and glass shows similarity to ena and VASP.

rough (ro) encodes a homeobox transcription factor required for proper specification of photoreceptor cells R2 and R5 in Drosophila eye development. To identify the transcriptional targets through which ro acts to specify the R2/R5 neuronal sub-type, we screened enhancer trap lines expressed in developing photoreceptors for those whose expression patterns were altered when ro function was inactivated. In this way we identified two potential ro targets, which are also targets of the zinc finger transcription factor glass (gl). We also identified an enhancer trap line that exhibits altered morphogenetic furrow expression in a ro mutant background. Finally, we have molecularly characterized an enhancer trap line, AE33, that was identified in earlier screens as a target of both ro and gl (freeman et al., 1992; Treisman and Rubin, 1996). The transcript interrupted by AE33 shares similarity with the mammalian vasodilator-stimulated phosphoprotein (VASP), a substrate for cAMP- and cGMP-dependent protein kinases that is associated with actin filaments, focal adhesions, and dynamic membrane regions (Haffner et al., 1995) with enabled (ena), a substrate of the Drosophila Abl tyrosine kinase (Gertler et al. 1995) and with two human Expressed Sequence Tags (ESTs).

Amino Acid Sequence↗
PubMed1996

The cell surface metalloprotease/disintegrin Kuzbanian is required for axonal extension in Drosophila.

It has long been suspected that proteolytic activity associated with advancing growth cones may be required for axon extension. We have isolated mutations in the kuzbanian (kuz) gene, which is expressed in the nervous system and encodes a putative zinc metalloprotease with a disintegrin domain. Drosophila embryos with loss-of-function mutations in kuz have dramatic defects in the development of central nervous system axon pathways, with many axons stalling and failing to extend through the nerve cord. This phenotype is rescued by panneural expression of kuz mRNA in the embryo. These results show that the Kuz metalloprotease is required for axon extension, suggesting a requirement for proteolytic activity at the growth cone surface.

Animals↗
PubMed1996

KSR modulates signal propagation within the MAPK cascade.

Kinase suppressor of Ras (KSR) is a recently identified component of Ras-dependent signaling pathways. In this report, we show that murine KSR1 (mKSR1) cooperates with activated Ras to promote Xenopus oocyte maturation and cellular transformation and provide evidence that this cooperation occurs by accelerating mitogen and extracellular regulated kinase (MEK) and mitogen-activated protein kinase (MAPK) activation. We also find that mKSR1 associates with Raf-1 at the plasma membrane in a Ras-dependent manner, indicating the presence of a membrane-bound kinase signaling complex. Although mKSR1 is related structurally to Raf-1, our findings reveal striking functional differences between these proteins. In marked contrast to the isolated amino- and carboxy-terminal domains of Raf-1, the KSR amino terminus also cooperates with Ras, whereas the carboxy-terminal kinase domain blocks Ras signaling as well as MEK and MAPK activation. The isolated KSR kinase domain suppressed Xenopus oocyte maturation, cellular transformation, and Drosophila eye development, suggesting that separation of the amino- and carboxy-terminal domains has uncoupled the normal regulation of KSR as a positive effector of Ras signaling. Together, our findings indicate that mKSR1 is an integral component of the MAPK module functioning via a novel mechanism to modulate signal propagation between Raf-1, MEK1, and MAPK.

3T3 Cells↗
PubMed1996

KUZ, a conserved metalloprotease-disintegrin protein with two roles in Drosophila neurogenesis.

During neurogenesis in Drosophila both neurons and nonneuronal cells are produced from a population of initially equivalent cells. The kuzbanian (kuz) gene described here is essential for the partitioning of neural and nonneuronal cells during development of both the central and peripheral nervous systems in Drosophila. Mosaic analyses indicated that kuz is required for cells to receive signals inhibiting the neural fate. These analyses further revealed that the development of a neuron requires a kuz-mediated positive signal from neighboring cells. The kuz gene encodes a metalloprotease-disintegrin protein with a highly conserved bovine homolog, raising the possibility that kuz homologs may act in similar processes during mammalian neurogenesis.

Amino Acid Sequence↗
PubMed1996

Loss of tramtrack gene activity results in ectopic R7 cell formation, even in a sina mutant background.

We have screened a collection of transposable-element-induced mutations for those which dominantly modify the extra R7 phenotype of a hypomorphic yan mutation. The members of one of the identified complementation groups correspond to disruptions of the tramtrack (ttk) gene. As heterozygotes, ttk alleles increase the percentage of R7 cells in yan mutant eyes. Just as yan mutations increase ectopic R7 cell formation, homozygous ttk mutant eye clones also contain supernumerary R7 cells. However, in contrast to yan, the formation of these cells in ttk mutant eye tissue is not necessarily dependent on the activity of the sina gene. Furthermore, although yan mutations dominantly interact with mutations in the Ras1, Draf, Dsor1, and rolled (rl) genes to influence R7 cell development, ttk mutations only interact with yan and rl gene mutations to affect this signaling pathway. Our data suggest that yan and ttk both function to repress inappropriate R7 cell development but that their mechanisms of action differ. In particular, TTK activity appears to be autonomously required to regulate a sina-independent mechanism of R7 determination.

Animals↗
PubMed1996

Pk92B: a Drosophila melanogaster protein kinase that belongs to the MEKK family.

A Drosophila melanogaster cDNA, encoding a protein with sequence similarity to the MEKK family of Ser/Thr kinases, was isolated from an eye-antennal imaginal disc cDNA library using a PCR-based approach. The deduced protein, Pk92B, has a kinase domain that is 40-48% identical to MEKK family members. The Pk92B gene was mapped to 92B8-10 on the third chromosome by in situ hybridization to polytene chromosomes.

Amino Acid Sequence↗
PubMed1996

Protein phosphatase 2A positively and negatively regulates Ras1-mediated photoreceptor development in Drosophila.

Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine phosphatase present in most tissues and cell types, has been implicated in the regulation of cell cycle progression, DNA replication, transcription, and translation. Here we present genetic evidence suggesting that PP2A functions downstream of Ras1 in the Sevenless receptor tyrosine kinase (RTK) signal transduction pathway that specifies R7 photoreceptor cell fate in the developing Drosophila eye. Ras1 and downstream cytoplasmic kinases, Raf, MEK, and MAPK, comprise an evolutionarily conserved cascade that mediates the transmission of signals from RTKs at the plasma membrane to specific factors in the nucleus. Using transgenic flies expressing constitutively activated Ras1 or Raf proteins that function independently of upstream signaling events, we show that a reduction in the dose of the gene encoding the catalytic subunit of PP2A stimulates signaling from Ras1 but impairs signaling from Raf. This suggests that PP2A both negatively and positively regulates the Ras1 cascade by dephosphorylating factors that function at different steps in the cascade.

Animals↗
PubMed1996

Targets of glass regulation in the Drosophila eye disc.

The Drosophila glass gene is required for the differentiation and survival of photoreceptors in the compound eye, ocelli and larval photoreceptor organ, glass encodes a zinc finger protein which can activate transcription in cell culture and is likely to act by regulating the expression of other genes. We have shown that it directly or indirectly controls the expression of approximately 25% of all enhancer trap lines expressed in the eye disc. glass gene activity is required to activate 19% of the lines, some of which express beta-galactosidase in photoreceptor subtype-specific patterns, and to repress 6%. The phenotype of eye discs doubly mutant for glass and the homeobox gene rough suggests that glass is required for subtype specification and for recruitment of cells to the ommatidial cluster.

Animals↗
PubMed1996

A screen for genes that function downstream of Ras1 during Drosophila eye development.

Cell-fate specification of the R7 photoreceptor cell is controlled by the sevenless receptor tyrosine kinase (SevRTK) and Ras1, the Drosophila homologue of mammalian H-ras, K-ras and N-ras oncogenes. An activated form of Ras1 expressed under control of the sevenless enhancer/promoter (sev-Ras1V12) induces production of supernumerary R7 photoreceptor cells, which causes the eye to become rough in appearance. To isolate mutations in genes functioning downstream of Ras1, we carried out a screen for dominant suppressors and enhancers of this rough eye phenotype. Approximately 850,000 mutagenized flies were screened, and 282 dominant suppressors and 577 dominant enhancers were isolated. Mutations in the Drosophila homologues of Raf, MEK, MAPK, type I Geranylgeranyl Transferase and Protein Phosphatase 2A were isolated, as were mutations in several novel signaling genes. Some of these mutant genes appear to be general signaling factors that function in other Ras1 pathways, while one seems to be more specific for photoreceptor development. At least two suppressors appear to function either between Ras1 and Raf or in parallel to Raf.

Animals↗
PubMed1995

Drosophila homologs of baculovirus inhibitor of apoptosis proteins function to block cell death.

Apoptotic cell death is a mechanism by which organisms eliminate superfluous or harmful cells. Expression of the cell death regulatory protein REAPER (RPR) in the developing Drosophila eye results in a small eye owing to excess cell death. We show that mutations in thread (th) are dominant enhancers of RPR-induced cell death and that th encodes a protein homologous to baculovirus inhibitors of apoptosis (IAPs), which we call Drosophila IAP1 (DIAP1). Overexpression of DIAP1 or a related protein, DIAP2, in the eye suppresses normally occurring cell death as well as death due to overexpression of rpr or head involution defective. IAP death-preventing activity localizes to the N-terminal baculovirus IAP repeats, a motif found in both viral and cellular proteins associated with death prevention.

Amino Acid Sequence↗
PubMed1995

KSR, a novel protein kinase required for RAS signal transduction.

We have identified and characterized two genes in Drosophila whose products are required for activated RAS to signal with normal efficiency, but do not appear to effect signaling by activated RAF. One encodes the beta subunit of type I geranylgeranyl transferase, a prenylation enzyme essential for targeting RAS to the plasma membrane. The other encodes a protein kinase that we have named kinase suppressor of ras (ksr). By genetic criteria, we show that KSR functions in multiple receptor tyrosine kinase pathways. We have isolated mammalian homologs of KSR that, together with the Drosophila gene, define a novel class of kinases. Our results suggest that KSR is a general and evolutionarily conserved component of the RAS signaling pathway that acts between RAS and RAF.

Amino Acid Sequence↗
PubMed1995

Gene disruptions using P transposable elements: an integral component of the Drosophila genome project.

Biologists require genetic as well as molecular tools to decipher genomic information and ultimately to understand gene function. The Berkeley Drosophila Genome Project is addressing these needs with a massive gene disruption project that uses individual, genetically engineered P transposable elements to target open reading frames throughout the Drosophila genome. DNA flanking the insertions is sequenced, thereby placing an extensive series of genetic markers on the physical genomic map and associating insertions with specific open reading frames and genes. Insertions from the collection now lie within or near most Drosophila genes, greatly reducing the time required to identify new mutations and analyze gene functions. Information revealed from these studies about P element site specificity is being used to target the remaining open reading frames.

Animals↗
PubMed1995

Cell proliferation and DNA replication defects in a Drosophila MCM2 mutant.

The yeast MCM2, MCM3, and MCM5/CDC46 genes are required for DNA replication and have been proposed to act as factors that license the DNA for one and only one round of replication per cell cycle. We have identified a Drosophila gene, DmMCM2, that is highly homologous to MCM2. A P-element insertion into this gene, which prevents its transcription, inhibits proliferation of cells in the imaginal discs and central nervous system (CNS) and causes an apparent prolongation of S phase in the embryonic and larval CNS. DmMCM2 is expressed in the embryo in a pattern corresponding to that of S-phase cells. These results suggest that DmMCM2 plays a role in the regulation of DNA replication analogous to that of its yeast counterpart.

Amino Acid Sequence↗
PubMed1995

Functional domain analysis of glass, a zinc-finger-containing transcription factor in Drosophila.

The glass gene is required for proper photo-receptor differentiation during development of the Drosophila eye glass codes for a DNA-binding protein containing five zinc fingers that we show is a transcriptional activator. A comparison of the sequences of the glass genes from two species of Drosophila and a detailed functional domain analysis of the Drosophila melanogaster glass gene reveal that both the DNA-binding domain and the transcriptional-activation domain are highly conserved between the two species. Analysis of the DNA-binding domain of glass indicates that the three carboxyl-terminal zinc fingers alone are necessary and sufficient for DNA binding. We also show that a deletion mutant of glass containing only the DNA-binding domain can behave in a dominant-negative manner both in vivo and in a cell culture assay that measures transcriptional activation.

Amino Acid Sequence↗
PubMed1995

Yan functions as a general inhibitor of differentiation and is negatively regulated by activation of the Ras1/MAPK pathway.

Drosophila yan has been postulated to act as an antagonist of the proneural signal mediated by the sevenless/Ras1/MAPK pathway. We have mutagenized the eight MAPK phosphorylation consensus sites of yan and examined the effects of overexpressing the mutant protein in transgenic flies and transfected S2 cultured cells. Our results suggest that phosphorylation by MAPK affects the stability and subcellular localization of yan, resulting in rapid down-regulation of yan activity. Furthermore, MAPK-mediated down-regulation of yan function appears to be critical for the proper differentiation of both neuronal and nonneuronal tissues throughout development, suggesting that yan is an essential component of a general timing mechanism controlling the competence of a cell to respond to inductive signals.

Alleles↗
PubMed1995

cAMP-dependent protein kinase and hedgehog act antagonistically in regulating decapentaplegic transcription in Drosophila imaginal discs.

Localized expression of decapentaplegic (dpp) is required for proper development of the Drosophila imaginal discs. Using genetic mosaics, we show that in the anterior compartment of appendage discs and anterior to the morphogenetic furrow in the eye disc, cells that lack cAMP-dependent protein kinase (PKA) activity ectopically express dpp. Pka- cells can influence the fate of neighboring cells to reorganize anterior patterns in appendages and trigger ectopic morphogenetic furrows in the developing retina. This organizing activity of Pka mutant cells depends on dpp activity. Our findings suggest that PKA is a component of a signaling pathway that represses dpp expression and that hh antagonizes this pathway to maintain dpp expression at the anterior-posterior compartment border and in the morphogenetic furrow.

Animals↗