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D Ish-Horowicz

Publications and source records attributed to D Ish-Horowicz.

At least 55 records · Page 3Linked to original sources
PubMed1990

X:A ratio, the primary sex-determining signal in Drosophila, is transduced by helix-loop-helix proteins.

Drosophila determines its sex by "counting" X chromosomes. We show that premature expression of the pair-rule segmentation gene hairy interferes with this process, resulting in female-specific lethality by inhibiting initiation of the master control gene Sex-lethal (Sxl). The female-specific lethality can be suppressed by a constitutive Sxl allele or by extra copies of X-linked "counting elements." These results are best explained by competition between hairy and other helix-loop-helix transcription factors that act in chromosome counting. We have confirmed this model by showing that misexpression of the achaete-scute T4 gene induces ectopic Sxl expression and male-specific lethality, confirming that achaete-scute T4 is the sisterless-b counting element. We propose that X chromosomes are counted through heterodimers of helix-loop-helix transcription factors that act synergistically to initiate Sxl expression.

Animals↗
PubMed1989

Autocatalytic ftz activation and metameric instability induced by ectopic ftz expression.

Inappropriate expression of the Drosophila pair-rule gene, fushi tarazu (ftz), causes cuticular pattern deletions apparently complementary to those in ftz larvae. We show that the two patterns actually originate similarly, in both cases affecting the even-numbered parasegmental boundaries. The reciprocal cuticular patterns derive from differing patterns of selector gene expression (homoeotic transformations). The primary effect of ectopic ftz activity is to broaden ftz domains by autocatalytic activation of endogenous ftz expression in an additional anterior cell. This activates engrailed (en) and represses wingless (wg) expression, consistent with their proposed combinatorial control by ftz (and other pair-rule genes) to define parasegmental primordia. We propose that the anterior margin of each ftz stripe is normally defined by the posterior even-skipped (eve) boundary.

Animals↗
PubMed1989

The Drosophila hairy protein acts in both segmentation and bristle patterning and shows homology to N-myc.

The Drosophila segmentation gene, hairy (h), acts to regulate embryonic segmentation and bristle pattern. We present the DNA sequence of the h gene and of h cDNAs, thereby deducing the organization of the h transcripts. The h gene encodes a 337 amino acid protein that acts in both embryonic segmentation and adult bristle patterning. The h protein includes a domain that shows extensive similarity to a domain of the proto-oncogene N-myc that may be involved in DNA binding and/or protein dimerization. We discuss mechanisms of h action as a transcriptional regulator.

Amino Acid Sequence↗
PubMed1989

Spatial control of hairy protein expression during embryogenesis.

We have used a polyclonal antiserum specific for the Drosophila segmentation gene, hairy (h), to analyse its expression during embryogenesis. The pattern of wild-type expression resembles that of h transcription, being expressed in stripes at the blastoderm stage. h is also expressed later in the stomodaeum, proctodaeum, tracheal pits and mesoderm. We demonstrate that h protein stripes show consistent phase relationships to those of the even-skipped (eve) pair-rule gene. We examine h protein patterns in embryos mutant for other segmentation genes, including h itself. We show that lack of h activity appears not to affect h striping, arguing that h expression is not under autoregulatory control. We also show that h activity is not needed for tracheal invagination. Mutations that are rearranged upstream of the h gene cause the loss of specific stripes, indicating that the h promoter includes activating elements that respond to specific spatial cues. Our observations suggest that pair-rule striping may be under redundant control, and we discuss possible implications for hierarchical models of pair-rule gene action.

Alleles↗
PubMed1987

Pattern abnormalities induced by ectopic expression of the Drosophila gene hairy are associated with repression of ftz transcription.

The pair-rule segmentation gene hairy (h) is expressed and required in alternate metameres in the early Drosophila embryo. We show that h expression outside these domains, driven by an hsp70 promoter, suppresses the expression of fushi tarazu (ftz). The kinetics of action favor h acting directly as a transcriptional repressor. The resulting pattern defects, and the patterns of en and Ubx activity, can be explained if h acts via ftz and other pair-rule genes in the establishment of stable en domains. We present evidence that ftz is required for the initiation of Ubx transcription, but not for its maintenance.

Animals↗
PubMed1987

A novel GC-rich dispersed repeat sequence in Drosophila melanogaster.

A novel family of dispersed repeat sequences from Drosophila melanogaster is described. Sequence analysis of two members of this family show them to contain greater than 75% GC bases. These are comprised of multiple repeats of GGX triplets interspersed occasionally with CGPy and TTPy. Southern blotting shows that these repeats are not transposable elements. Twenty four homologous recombinants have been localised by in situ hybridization to seven sites in the Drosophila genome. Polyadenylated RNAs homologous to this repeat family are expressed in a complex pattern which is developmentally regulated. We suggest that this family encodes a set of glycine-rich domains in Drosophila proteins.

Animals↗
PubMed1986

Correlative changes in homoeotic and segmentation gene expression in Krüppel mutant embryos of Drosophila.

Mutations of the segmentation gene Krüppel (Kr) cause deletions of contiguous sets of body segments from the middle region of the Drosophila embryo. We have monitored expression in situ of three other genes implicated in the establishment of the body plan, namely hairy (h), fushi tarazu (ftz) and engrailed (en), in mutant Kr embryos. Our results show that the pattern of expression of all three genes depends upon Kr activity and are consistent with a hierarchical model of segmentation gene activity. In addition, we find that the initial expression of the homoeotic selector gene Ultrabithorax(Ubx) follows a novel pattern in Kr embroys indicating a close integration of the spatial control of homoeotic and segmantation gene expression.

Journal Article↗
PubMed1986

Functional analysis of the transcriptional control regions of the copia transposable element.

The introduction of copia-based vectors in Drosophila hydei cells results in their high-level transient expression and the subsequent establishment of stably transformed cell lines containing multiple copies of vector integrated into host genomic DNA. Using transformation frequency and transient expression analysis as assays of promoter strength, we have defined the regions of copia essential for expression. We find that the essential sequences reside within the long terminal repeat, but 3' to the site of initiation of copia RNA. Deletion of the consensus enhancer-like sequences from copia appears to have no effect on vector expression.

Journal Article↗
PubMed1984

An assay for transient gene expression in transfected Drosophila cells, using [3H]guanine incorporation.

We have developed an assay for transient gene expression using a dominant-selectable marker previously employed to transform Drosophila cultured cells. Drosophila hydei cells transfected with a functional Escherichia coli xanthine guanine phosphoribosyl transferase gene (gpt), under the control of the long terminal repeats (LTRs) of the copia transposable element, rapidly incorporate guanine into acid-precipitable counts. Autoradiographic analysis in situ shows that approximately 20% of cells take up, and express, the gpt gene. This transient gpt expression depends on the Drosophila promoter sequences since vectors with the gpt gene in reverse orientation to the copia LTRs fail to incorporate guanine. Deletion analysis confirms that the LTRs are essential for gpt gene expression. Similarly, cells transfected with gpt controlled by the Drosophila 70 000 mol. wt. heat-shock (hsp 70) promoter show regulated guanine incorporation when heat shocked. The efficiency of the copia LTRs varies considerably between the cell lines we tested, whereas that of the hsp 70 promoter does not. The heterologous promoters of the Rous sarcoma virus (RSV) and simian virus 40 (SV40) function poorly in these cells.

Animals↗
PubMed1984

Rescue of a Drosophila temperature-sensitive mutant cell line by DNA transfection.

At the nonpermissive temperature, the shibirets gene of Drosophila causes adult paralysis and cell death during development. We have used DNA-mediated gene transfer with wild-type genomic DNA to rescue the lethal phenotype of shits cultured cells and have isolated cell lines which grow at the nonpermissive temperature of 29 degrees C. By using restriction endonucleases, we confirm that this rescue is DNA sequence dependent. Further, cells cotransfected with wild-type genomic DNA and plasmid DNA contain plasmid sequences when selected for survival at 29 degrees C. This confirms the uptake of DNA by the transformed cells and provides a simple temperature selection technique allowing coselection of genes which cannot themselves be selected for.

Animals↗
PubMed1984

Integration of Drosophila heat-shock genes transfected into cultured Drosophila melanogaster cells.

We have used DNA-mediated gene transfer to introduce into Drosophila melanogaster cells DNA sequences for which no selective criteria exist. We have introduced a Drosophila heat-shock locus into cultured Drosophila cells by calcium phosphate cotransfection with the copia vector pCV31gpt and selection for xanthine utilization. We recovered cell lines containing between three and about 50 copies of both pCV31gpt and pMH10A, a cloned 87 A7 hsp70 heat-shock locus that encodes a mutant 40,000-dalton heat-shock protein (hsp40). The stable inheritance of the transformed DNAs argues that the input DNAs have integrated into the genome. We show that this is indeed the case for one cell line by cloning back the transfected DNA and detecting the flanking chromocentral sequences by in situ hybridization. Surprisingly, the integrated hsp70 genes are not expressed. This report represents the first example of the cointroduction of DNA sequences into Drosophila cells by cotransfection with a dominant selectable marker.

Animals↗
PubMed1983

The origin of extrachromosomal circular copia elements.

Cloned extrachromosomal circular copia elements were studied by nucleotide sequence and restriction enzyme analysis to determine their mechanisms of formation and their possible roles in copia transposition. Rearranged circular copias containing inverted segments flanked by 5 bp sequence duplication were observed, suggesting that circular copias are capable of integrating into their own sequences. Such copia circles are analogous to similarly rearranged retrovirus circles, strengthening the relationship between the copia-like elements and retroviruses. There is marked sequence heterogeneity at the junction between the fused terminal direct repeats of seven copia circles. The junctions contain 0-15 bp inserts, the sequences of which are inconsistent with the creation of these particular molecules by reverse transcription.

Animals↗
PubMed1982

Expression of Drosophila heat shock genes is regulated in Rat-cells.

We have introduced a Drosophila 87A heat shock locus into the genome of Rat-1 cells. A brief heat shock of a resultant transformed line, Rhs11, induces the transcription of the Drosophila heat shock genes from the Drosophila heat shock promoter. This suggests that the induction mechanism and regulatory sequences for the heat shock response have been conserved between Drosophila and mammals.

Animals↗
PubMed1981

Genomic organization and transcription of the alpha beta heat shock DNA in Drosophila melanogaster.

Previous studies have shown that (i) several RNAs induced by heat shock of Drosophila melanogaster cells are homologous to tandemly repeated alpha beta units found in cloned segments of D. melanogaster DNA, and (ii) the alpha beta sequences are present both at a major heat shock locus, 87Cl, and the chromocenter of polytene chromosomes (Lis, J.T., Prestidge, L. and Hogness, D.S. [1978] Cell 14, 901-919). We have used deficiencies that delete DNA from the 87C region to examine the arrangement of alpha beta sequences at this locus and in the centromeric heterochromatin that comprises the chromocenter, and also to determine the chromosomal location of the induced transcription. The tandemly repeated alpha beta units are restricted to the 87C locus. In contrast, the chromocentral alpha beta sequences do not form intact alpha beta units, and are dispersed at heterochromatic sites in some other form. Although only half of the alpha beta DNA is at the 87C locus, essentially all alpha beta transcripts (greater than 99.5%) are derived from this locus.

Animals↗