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D Ish-Horowicz

Publications and source records attributed to D Ish-Horowicz.

At least 37 records · Page 2Linked to original sources
PubMed1997

A chimeric enhancer-of-split transcriptional activator drives neural development and achaete-scute expression.

Drosophila melanogaster neurogenesis requires the opposing activities of two sets of basic helix-loop-helix (bHLH) proteins: proneural proteins, which confer on cells the ability to become neural precursors, and the Enhancer-of-split [E(spl)] proteins, which restrict such potential as part of the lateral inhibition process. Here, we test if E(spl) proteins function as promoter-bound repressors by examining the effects on neurogenesis of an E(spl) derivative containing a heterologous transcriptional activation domain [E(spl) m7Act (m7Act)]. In contrast to the wild-type E(spl) proteins, m7Act efficiently induces neural development, indicating that it binds to and activates target genes normally repressed by E(spl). Mutations in the basic domain disrupt m7Act activity, suggesting that its effects are mediated through direct DNA binding. m7Act causes ectopic transcription of the proneural achaete and scute genes. Our results support a model in which E(spl) proteins normally regulate neurogenesis by direct repression of genes at the top of the neural determination pathway.

Animals↗
PubMed1997

Torso signalling regulates terminal patterning in Drosophila by antagonising Groucho-mediated repression.

Patterning of the non-segmental termini of the Drosophila embryo depends on signalling via the Torso receptor tyrosine kinase (RTK). Activation of Torso at the poles of the embryo triggers restricted expression of the zygotic gap genes tailless (tll) and huckebein (hkb). In this paper, we show that the Groucho (Gro) corepressor acts in this process to confine terminal gap gene expression to the embryonic termini. Embryos lacking maternal gro activity display ectopic tll and hkb transcription; the former leads, in turn, to lack of abdominal expression of the Krüppel and knirps gap genes. We show that torso signalling permits terminal gap gene expression by antagonising Gro-mediated repression. Thus, the corepressor Gro is employed in diverse developmental contexts and, probably, by a variety of DNA-binding repressors.

Abdomen↗
PubMed1996

In vivo interactions of the Drosophila Hairy and Runt transcriptional repressors with target promoters.

The Hairy and Runt pair-rule proteins regulate Drosophila segmentation by repressing transcription. To explore the ability of these proteins to function as promoter-bound regulators in vivo, we examined the effects of Hairy and Runt derivatives containing heterologous transcriptional activation domains (HairyAct and RunAct). Using this approach, we find that Hairy and Runt efficiently target such activation domains to specific segmentation gene promoters, leading to rapid induction of transcription. Our results strongly suggest that Hairy normally acts as a promoter-bound repressor of fushi tarazu, runt and odd-skipped, and that Runt directly represses even-skipped. We also show that expressing HairyAct in early blastoderm embryos causes ectopic Sex-lethal expression and male-specific lethality, implying that the Hairy-related denominator element Deadpan represses Sex-lethal during sex determination by directly recognizing the early Sex-lethal promoter.

Animals↗
PubMed1996

A chick homologue of Serrate and its relationship with Notch and Delta homologues during central neurogenesis.

In the Drosophila nervous system, lateral inhibition regulates commitment to a neural fate by preventing neighbouring cells from developing alike. This signalling process is mediated by two transmembrane proteins-Notch as receptor and Delta as its ligand. The Delta-related protein Serrate also acts as a Notch ligand in Drosophila, but in a different developmental process that organizes patterning of the wing. We have previously shown that lateral inhibition operates at early stages of neurogenesis in vertebrates, via genes homologous to Drosophila Delta and Notch. We report here the cloning of a chick Serrate homologue, C-Serrate-1. This gene is expressed in the central nervous system, as well as in the cranial placodes, nephric epithelium, vascular system, and distal limb-bud mesenchyme. In most of these sites, its expression is associated with expression of C-Notch-1 and C- Delta-1. All three genes are expressed in the ventricular zone of the hindbrain and spinal cord, throughout the period when neurons are being born. Within this zone, C-Delta-1 and C-Serrate-1 are expressed in complementary subsets of nondividing cells that appear to be nascent neurons: C- Serrate-1 expression is restricted to specific locations along the dorsoventral axis, forming narrow bands extending from the anterior hindbrain to the tail. Our observations strongly suggest that Delta-Notch signalling delivers lateral inhibition not only early but throughout vertebrate neurogenesis to regulate neuronal commitment, and that Serrate-Notch signalling may act similarly in this process. By analogy with its role in Drosophila wing patterning, C-Serrate-1 may also have a role in organising the dorso-ventral pattern of the neural tube. We argue that signalling via Notch maintains neurogenesis, both in vertebrates and in flies, by keeping a proportion of the neuroepithelial cells in an uncommitted stem-cell-like state.

Amino Acid Sequence↗
PubMed1996

Asymmetric localization of Drosophila pair-rule transcripts from displaced nuclei: evidence for directional nuclear export.

Drosophila pair-rule transcripts accumulate exclusively apical of the layer of peripheral nuclei in syncytial blastoderm stage embryos. Here, we use aneuploid embryos to test zygotic gene requirements for pair-rule transcript localization. As apical localization is maintained in all genotypes tested, the required components must be maternally encoded. In aneuploid embryos with multiple layers or cortical nuclei, pair-rule transcripts lie apical of both superficial and internalized nuclei. In the latter case, the transcripts are 'pseudo-apical', i.e. apical of the nuclei from which they derive, but basal of superficial nuclei. We show that internalized nuclei maintain their apico-basal nuclear orientation, and that they lack the apical cytoskeletal assemblies which lie adjacent to superficial nuclei. These results support a mechanism of localizing pair-rule transcripts by directional (vectorial) nuclear export.

Aneuploidy↗
PubMed1995

Primary neurogenesis in Xenopus embryos regulated by a homologue of the Drosophila neurogenic gene Delta.

X-Delta-1, a Xenopus homologue of the Drosophila Delta gene, is expressed in the early embryonic nervous system in scattered cells that appear to be the prospective primary neurons. Ectopic X-Delta-1 activity inhibits production of primary neurons and interference with endogenous X-Delta-1 activity results in overproduction of primary neurons. These results indicate that the X-Delta-1 protein mediates lateral inhibition delivered by prospective neurons to adjacent cells, and that commitment to a neural fate in vertebrates is regulated by Delta-Notch signalling as in Drosophila.

Animals↗
PubMed1995

Expression of a Delta homologue in prospective neurons in the chick.

The product of the Delta gene, acting as ligand, and that of the Notch gene, acting as receptor, are key components in a lateral-inhibition signalling pathway that regulates the detailed patterning of many different tissues in Drosophila. During neurogenesis in particular, neural precursors, by expressing Delta, inhibit neighbouring Notch-expressing cells from becoming committed to a neural fate. Vertebrates are known to have several Notch genes, but their functions are unclear and their ligands hitherto unidentified. Here we identify and describe a chick Delta homologue, C-Delta-1. We show that C-Delta-1 is expressed in prospective neurons during neurogenesis, as new cells are being born and their fates decided. Our data from the chick, combined with parallel evidence from Xenopus, suggest that both the Delta/Notch signalling mechanism and its role in neurogenesis have been conserved in vertebrates.

Amino Acid Sequence↗
PubMed1994

Groucho is required for Drosophila neurogenesis, segmentation, and sex determination and interacts directly with hairy-related bHLH proteins.

We have used the interaction trap, a yeast two-hybrid system, to identify proteins interacting with hairy, a basic-helix-loop-helix (bHLH) protein that represses transcription during Drosophila embryonic segmentation. We find that the groucho (gro) protein binds specifically to hairy and also to hairy-related bHLH proteins encoded by deadpan and the Enhancer of split complex. The C-terminal WRPW motif present in all these bHLH proteins is essential for this interaction. We demonstrate that these associations reflect in vivo maternal requirements for gro during neurogenesis, segmentation, and sex determination, three processes regulated by the above bHLH proteins, and we propose that gro is a transcriptional corepressor recruited to specific target promoters by hairy-related bHLH proteins.

Animals↗
PubMed1994

Specific DNA recognition and intersite spacing are critical for action of the bicoid morphogen.

We examined DNA site recognition by Bicoid and its importance for pattern formation in developing Drosophila embryos. Using altered DNA specificity Bicoid mutants and appropriate reporter genes, we show that Bicoid distinguishes among related DNA-binding sites in vivo by a specific contact between amino acid 9 of its recognition alpha-helix (lysine 50 of the homeodomain) and bp 7 of the site. This result is consistent with our earlier results using Saccharomyces cerevisiae but differs from that predicted by crystallographic analysis of another homeodomain-DNA interaction. Our results also demonstrate that Bicoid binds directly to those genes whose transcription it regulates and that the amino acid 9 contact is necessary for Bicoid to direct anterior pattern formation. In both Drosophila embryos and yeast cells, Bicoid requires multiple binding sites to activate transcription of target genes. We find that the distance between binding sites is critical for Bicoid activation but that, unexpectedly, this critical distance differs between Drosophila and S. cerevisiae. This result suggests that Bicoid activation in Drosophila might require an ancillary protein(s) not present in S. cerevisiae.

Animals↗
PubMed1993

achaete-scute feminizing activities and Drosophila sex determination.

Sex determination in Drosophila depends on X-linked 'numerator' genes activating early Sex-lethal (Sxl) transcription in females. One numerator gene, sisterless-b (sis-b), corresponds to the achaete-scute (AS-C) T4 basic-helix-loop-helix (bHLH) gene. Two other closely related AS-C bHLH genes, T3 and T5, appear not to function as numerator elements. We analyzed endogenous AS-C expression and show that T4 is the major AS-C numerator gene because it is expressed earlier and more strongly than are T3 and T5. Only T4 expression is detectable during the early syncytial stages when Sxl state is being determined. Nevertheless, the effects of ectopic AS-C gene expression show that T3 and T5 proteins display weak but significant feminizing activities, enhancing male-lethality, and rescuing the female-lethality of sis mutations. Detailed examination of Sxl expression in rescued embryos suggests that female cells may be viable in the absence of detectable Sxl protein expression.

Animals↗
PubMed1993

Drosophila hairy pair-rule gene regulates embryonic patterning outside its apparent stripe domains.

The hairy (h) segmentation gene of Drosophila regulates segmental patterning of the early embryo, and is expressed in a set of anteroposterior stripes during the blastoderm stage. We have used a set of h gene deletions to study the h promoter and the developmental requirements for individual h stripes. The results confirm upstream regulation of h striping but indicate that expression in the anterodorsal head domain depends on sequences downstream of the two transcription initiation sites. Surprisingly, the two anterior-most h domains appear to be dispensable for head development and embryonic viability. One partial promoter deletion expresses ectopic h, leading to misexpression of other segmentation genes and embryonic pattern defects. We demonstrate that h affects patterning outside its apparent stripe domains, supporting a model in which primary pair-rule genes act as concentration-dependent transcriptional regulators, i.e. as local morphogens.

Animals↗
PubMed1992

Point mutations in the Drosophila hairy gene demonstrate in vivo requirements for basic, helix-loop-helix, and WRPW domains.

The Drosophila pair-rule gene, hairy (h), encodes a nuclear basic helix-loop-helix (bHLH) protein that regulates embryonic segmentation and adult bristle patterning. In both cases, the h protein behaves as a transcriptional repressor. In this study, we determined the molecular nature of 12 h alleles. One mutation maps within the HLH domain, consistent with h function requiring homodimerization or heterodimerization with other HLH proteins. A second mutation lies in the basic domain, suggesting that DNA binding is required for h activity. Several mutations show that the h C terminus, in particular the WRPW domain, is also required for h activity, perhaps by interacting with other proteins to mediate transcriptional repression. We show that the h protein in Drosophila virilis closely resembles that in D. melanogaster and includes completely conserved bHLH and WRPW domains.

Amino Acid Sequence↗
PubMed1991

Apical localization of pair-rule transcripts requires 3' sequences and limits protein diffusion in the Drosophila blastoderm embryo.

The peripheral cytoplasm (periplasm) of the Drosophila blastoderm embryo is subdivided into apical and basal compartments by a layer of nuclei. We have demonstrated three classes of periplasmic transcript localization: apical, basal, and unlocalized (apical and basal), each of which depends on 3' sequences. We define 3' apical localization signals within the even-skipped, fushi tarazu, and hairy pair-rule segmentation genes and the alpha 1-tubulin and bicoid genes. 3' human alpha-globin sequences direct transcripts basally. Transcript destination depends on transcript structure, not on transcript stability or chromosomal location. Apical transcripts direct apical compartmentalization of cytoplasmic protein. We propose that apical localization of pair-rule transcripts restricts lateral protein diffusion, thereby allowing pair-rule proteins to define sharp boundaries and precise spatial domains.

Animals↗
PubMed1991

wimp, a dominant maternal-effect mutation, reduces transcription of a specific subset of segmentation genes in Drosophila.

wimp is a dominant maternal-effect mutation that interacts with a specific subset of early-acting maternal and zygotic Drosophila genes. We show that wimp is a change-of-function mutation, allelic to mutations of the 140-kD subunit of RNA polymerase, which causes reduced transcription of interacting genes. Loci that do not interact with wimp are expressed at normal levels. We discuss these results in terms of specific interactions between transcription factors and RNA polymerase. Embryos from wimp mothers show unaltered fate maps and develop normally, despite the reduction of transcript levels at least twofold. We suggest that spatial cues are determined by a balance of segmentation gene products rather than their absolute concentrations. We also demonstrate powerful genetic screens for otherwise undetected loci required for segmentation, sex determination, and other early functions.

Alleles↗
PubMed1991

Individual stripe regulatory elements in the Drosophila hairy promoter respond to maternal, gap, and pair-rule genes.

Striped expression of the pair-rule gene hairy (h) plays a central role in regulating segmentation in Drosophila. We have used h-lacZ reporter gene fusions to delineate h sequences that drive individual stripe expression. We show that 14 kb of 5'-flanking DNA directs expression of seven lacZ stripes in the blastoderm embryo. Within this region, we identify discrete sequences required for expression of individual stripes 1, 5, 6, and 7, and dispersed elements active in the stripe 2 domain. Only the stripe 1 element directs lacZ expression in an accurate h stripe; stripes 5, 6, and 7 are displaced by one to two cells relative to their h counterparts. These results indicate that regulatory sequences are dispersed within the h promoter. We have determined the sensitivity of the lacZ stripes to maternal, gap, and pair-rule gene mutations. Our results suggest that different but overlapping subsets of gap genes regulate each stripe and that activation and repression are both important in generating the stripe pattern.

Animals↗
PubMed1991

Mis-regulating segmentation gene expression in Drosophila.

We have used the hunchback (hb) gap-gene promoter to drive ectopic expression of the pair-rule genes fushi tarazu (ftz), even-skipped (eve) and hairy (h). Unexpectedly, flies transformed with such constructs are viable, despite spatial and temporal mis-regulation of pair-rule expression caused by the fusion genes. We show that fusion gene expression is transcriptionally regulated, such that ectopic expression is suppressed when pattern is established, and present evidence indicating that interstripe hb-ftz expression is repressed by eve. These results are considered in terms of redundant control of pair-rule gene striping. We also discuss the potential dangers of using mis-regulated gene expression to analyse normal function.

Animals↗