PubMed Health⌕ Search

Biomedical subjects

I B Dawid

Publications and source records attributed to I B Dawid.

At least 19 recordsLinked to original sources
PubMed1996

Molecular cloning, structure, and chromosomal localization of the mouse LIM/homeobox gene Lhx5.

Lhx5, the mouse ortholog of the Xenopus Xlim-5, is a LIM/homeobox gene expressed in the central nervous system during both embryonic development and adulthood. During development its domain of expression is mainly localized at the most anterior portion of the neural tube, and it precedes the morphological differentiation of the forebrain; for this reason we believe that Lhx5 could play an important role in forebrain patterning. Here we present the structural organization and the chromosomal localization of the Lhx5 gene. The gene is composed of five exons spanning more than 10 kb of genomic sequence. The first and second LIM domains are encoded by the first and second exon, while the codons of the homeobox are split between the third and the fourth exons. The structure of Lhx5 is similar to that of other LIM/homeodomain proteins, Lhx1/lim1 and Lhx3/lim3, but differs from that of other LIM genes, such as mec3 and LMO1/Rbtn1, in which the codons for the LIM domains are interrupted by introns. We have mapped Lhx5 to the central region of mouse chromosome 5.

Animals↗
PubMed1996

Retinoid X receptor-selective ligands produce malformations in Xenopus embryos.

Retinoids exert pleiotropic effects on the development of vertebrates through the action of retinoic acid receptors (RAR) and retinoid X receptors (RXR). We have investigated the effect of synthetic retinoids selective for RXR and RAR on the development of Xenopus and zebrafish embryos. In Xenopus, both ligands selective for RAR and RXR caused striking malformations along the anterior-posterior axis, whereas in zebrafish only ligands specific for RAR caused embryonic malformations. In Xenopus, RAR- and RXR-selective ligands regulated the expression of the Xlim-1, gsc, and HoxA1 genes similarly as all-trans-retinoic acid. Nevertheless, RXR-selective ligands activated only an RXR responsive reporter but not an RAR responsive reporter introduced by microinjection into the Xenopus embryo, consistent with our failure to detect conversion of an RXR-selective ligand to different derivatives in the embryo. These results suggest that Xenopus embryos possess a unique response pathway in which liganded RXR can control gene expression. Our observations further illustrate the divergence in retinoid responsiveness between different vertebrate species.

Animals↗
PubMed1996

The LIM homeodomain protein Lim-1 is widely expressed in neural, neural crest and mesoderm derivatives in vertebrate development.

Polyclonal antibodies to Xlim-1 homeodomain protein of Xenopus laevis were used to study the developmental expression pattern of this protein in Xenopus, rat and mouse. Western blotting of embryo extracts injected with different Xlim-1 constructs confirmed the specificity of the antibody. Beginning at the gastrula stage, Xlim-1 protein was detected in three cell lineages: (i) notochord, (ii) pronephros and (iii) certain regions of the central nervous system, in agreement with earlier studies of the expression of Xlim-1 RNA (Taira et al., Development 120: 1525-1536, 1994a). In addition, several new locations of Xlim-1 expression were found, including the olfactory organ, retina, otic vesicle, dorsal root ganglia and adrenal gland. Similar expression patterns were seen for the Lim-1 protein in frog and rodent tissues. These observations implicate the Xlim-1 gene in the specification of multiple cell lineages, particularly within the nervous system, and emphasize the conserved nature of the role of this gene in different vertebrate animals.

Animals↗
PubMed1995

Glycogen synthase kinase-3 and dorsoventral patterning in Xenopus embryos.

Glycogen synthase kinase 3 (GSK-3) is homologous to the product of the Drosophila gene shaggy (zeste-white 3), which is required for signalling by wingless during Drosophila development. To test whether GSK-3 is also involved in vertebrate pattern formation, its role was investigated during early Xenopus development. It was found that dominant-negative GSK-3 mutants induced dorsal differentiation, whereas wild-type GSK-3 induced ventralization. These results indicate that GSK-3 is required for ventral differentiation, and suggest that dorsal differentiation may involve the suppression of GSK-3 activity by a wingless/wnt-related signal.

Animals↗
PubMed1995

Chicken interferon consensus sequence-binding protein (ICSBP) and interferon regulatory factor (IRF) 1 genes reveal evolutionary conservation in the IRF gene family.

Members of the IRF family mediate transcriptional responses to interferons (IFNs) and to virus infection. So far, proteins of this family have been studied only among mammalian species. Here we report the isolation of cDNA clones encoding two members of this family from chicken, interferon consensus sequence-binding protein (ICSBP) and IRF-1. The predicted chicken ICSBP and IRF-1 proteins show high levels of sequence similarity to their corresponding human and mouse counterparts. Sequence identities in the putative DNA-binding domains of chicken and human ICSBP and IRF-1 were 97% and 89%, respectively, whereas the C-terminal regions showed identities of 64% and 51%; sequence relationships with mouse ICSBP and IRF-1 are very similar. Chicken ICSBP was found to be expressed in several embryonic tissues, and both chicken IRF-1 and ICSBP were strongly induced in chicken fibroblasts by IFN treatment, supporting the involvement of these factors in IFN-regulated gene expression. The presence of proteins homologous to mammalian IRF family members, together with earlier observations on the occurrence of functionally homologous IFN-responsive elements in chicken and mammalian genes, highlights the conservation of transcriptional mechanisms in the IFN system, a finding that contrasts with the extensive sequence and functional divergence of the IFNs.

Amino Acid Sequence↗
PubMed1995

Expression pattern of the murine LIM class homeobox gene Lhx3 in subsets of neural and neuroendocrine tissues.

Murine Lhx3 cDNA isolated from the mouse pituitary cDNA library encodes a LIM-type homeodomain protein that contains two tandemly repeated LIM domains and the homeodomain. The identities of predicted amino acid sequences between the mouse of Lhx3 and Xenopus Xlim-3 genes are 80, 95, and 97% in the LIM domains 1 and 2, and the homeodomain, respectively, and 84% in the entire protein. 5'-RACE procedures and genomic cloning revealed that two distinct N-terminal sequences arise from two different exons 1a and 1b. Exon 1a encodes a sequence similar to that of Xlim-3, whereas exon 1b encodes a different N-terminus. It is likely that there are two transcription initiation sites in the Lhx3 gene. The Lhx3 transcripts were detected by whole mount in situ hybridization as early as day E9.5 post coitum in Rathke's pouch and the closing neural tube. During subsequent development, Lhx3 expression was observed in the anterior and intermediate but not in the posterior lobes of the pituitary, and in the ventral hindbrain and spinal cord. Northern blot analysis of adult tissues showed that Lhx3 mRNA persists in the pituitary. The expression pattern of Lhx3 is well conserved between Xenopus and mouse, underscoring the functional importance of this gene as a regulator of development. A number of established cell lines of pituitary origin express Lhx3 and therefore constitute a useful tool for further study of Lhx3 gene function.

Amino Acid Sequence↗
PubMed1995

The LIM class homeobox gene lim5: implied role in CNS patterning in Xenopus and zebrafish.

LIM homeobox genes are characterized by encoding proteins in which two cysteine-rich LIM domains are associated with a homeodomain. We report the isolation of a gene, named Xlim-5 in Xenopus and lim5 in the zebrafish, that is highly similar in sequence but quite distinct in expression pattern from the previously described Xlim-1/lim1 gene. In both species studied the lim5 gene is expressed in the entire ectoderm in the early gastrula embryo. The Xlim-5 gene is activated in a cell autonomous manner in ectodermal cells, and this activation is suppressed by the mesoderm inducer activin. During neurulation, expression of the lim5 gene in both the frog and fish embryo is rapidly restricted to an anterior region in the developing neural plate/keel. In the 2-day Xenopus and 24-hr zebrafish embryo, this region becomes more sharply defined, forming a strongly lim5-expressing domain in the diencephalon anterior to the midbrain-forebrain boundary. In addition, regions of less intense lim5 expression are seen in the zebrafish embryo in parts of the telencephalon, in the anterior diencephalon coincident with the postoptic commissure, and in restricted regions of the midbrain, hindbrain, and spinal cord. Expression in ventral forebrain is abolished from the 5-somite stage onward in cyclops mutant fish. These results imply a role for lim5 in the patterning of the nervous system, in particular in the early specification of the diencephalon.

Amino Acid Sequence↗
PubMed1995

Motoneuron fate specification revealed by patterned LIM homeobox gene expression in embryonic zebrafish.

In zebrafish, individual primary motoneurons can be uniquely identified by their characteristic cell body positions and axonal projection patterns. The fate of individual primary motoneurons remains plastic until just prior to axogenesis when they become committed to particular identities. We find that distinct primary motoneurons express particular combinations of LIM homeobox genes. Expression precedes axogenesis as well as commitment, suggesting that LIM homeobox genes may contribute to the specification of motoneuronal fates. By transplanting them to new spinal cord positions, we demonstrate that primary motoneurons can initiate a new program of LIM homeobox gene expression, as well as the morphological features appropriate for the new position. We conclude that the patterned distribution of different primary motoneuronal types within the zebrafish spinal cord follows the patterned expression of LIM homeobox genes, and that this reflects a highly resolved system of positional information controlling gene transcription.

Amino Acid Sequence↗
PubMed1995

Nodal induces ectopic goosecoid and lim1 expression and axis duplication in zebrafish.

One of the first intercellular signalling events in the vertebrate embryo leads to mesoderm formation and axis determination. In the mouse, a gene encoding a new member of the TGF-beta superfamily, nodal, is disrupted in a mutant deficient in mesoderm formation (Zhou et al., 1993, Nature 361, 543). nodal mRNA is found in prestreak mouse embryos, consistent with a role in the development of the dorsal axis. To examine the biological activities of nodal, we have studied the action of this factor in eliciting axis determination in the zebrafish, Danio rerio. Injection of nodal mRNA into zebrafish embryos caused the formation of ectopic axes that included notochord and somites. Axis duplication was preceded by the generation of an apparent ectopic shield (organizer equivalent) in nodal-injected embryos, as indicated by the appearance of a region over-expressing gsc and lim1; isolation and expression in the shield of the lim1 gene is reported here. These results suggest a role for a nodal-like factor in pattern formation in zebrafish.

Amino Acid Sequence↗
PubMed1995

Dorsal-ventral patterning and differentiation of noggin-induced neural tissue in the absence of mesoderm.

In Xenopus development, dorsal mesoderm is thought to play a key role in both induction and patterning of the nervous system. Previously, we identified a secreted factor, noggin, which is expressed in dorsal mesoderm and which can mimic that tissue's neural-inducing activity, without inducing mesoderm. Here the neural tissue induced in ectodermal explants by noggin is further characterized using four neural-specific genes: two putative RNA-binding proteins, nrp-1 and etr-1; the synaptobrevin sybII; and the lipocalin cpl-1. First we determine the expression domain of each gene during embryogenesis. Then we analyze expression of these genes in noggin-treated explants. All markers, including the differentiated marker sybII, are expressed in noggin-induced neural tissue. Furthermore, cpl-1, a marker of dorsal brain, and etr-1, a marker absent in much of the dorsal forebrain, are expressed in non-overlapping territories within these explants. We conclude that the despite the absence of mesoderm, noggin-induced neural tissue shows considerable differentiation and organization, which may represent dorsal-ventral patterning of the forebrain.

Amino Acid Sequence↗
PubMed1995

LIM domain proteins.

The LIM domain is a cysteine-rich domain composed of 2 special zinc fingers that are joined by a 2-amino acid spacer. Some proteins are constituted by LIM domains only while others contain a variety of different functional domains. LIM proteins form a diverse group which includes transcription factors and cytoskeletal proteins. The primary role of LIM domains appears to be in protein-protein interaction, through the formation of dimers with identical or different LIM domains or by binding distinct proteins. In LIM homeodomain proteins, LIM domains seem to function as negative regulatory domains. LIM homeodomain proteins are involved in the control of cell lineage determination and the regulation of differentiation, and LIM-only proteins may have similar roles. LIM-only proteins are also implicated in the control of cell proliferation since several genes encoding such proteins are associated with oncogenic chromosome translocations. In analyzing sequence relationships between LIM domains we suggest that they may be arranged into 5 groups which appear to correlate with the structural and functional properties of the proteins containing these domains.

Amino Acid Sequence↗
PubMed1994

Role of the LIM class homeodomain protein Xlim-1 in neural and muscle induction by the Spemann organizer in Xenopus.

Like all known LIM class homeobox genes, Xlim-1 encodes a protein with two tandemly repeated cysteine-rich LIM domains upstream of the homeodomain. In Xenopus laevis, Xlim-1 is specifically expressed in the Spemann organizer, whose major functions include neural induction and dorsalization of ventral mesoderm. From RNA injection experiments we conclude here that: (1) the LIM domains behave as negative regulatory domains; (2) LIM domain mutants of Xlim-1 elicited neural differentiation in animal explants; (3) mutant, and to a lesser extent wild-type, Xlim-1 enhanced muscle formation after coinjection with Xbra; (4) both of these activities are mediated by extracellular signals as seen in combined explant experiments; (5) Xlim-1 mutants activated goosecoid (gsc) expression in animal explants, but not expression of noggin or follistatin; (6) mutant Xlim-1 elicited formation of partial secondary axes, and cooperated with gsc in notochord formation. Thus Xlim-1 has latent activities, implicating it in organizer functions.

Animals↗
PubMed1994

Vertical versus planar neural induction in Rana pipiens embryos.

The neural plate in the amphibian embryo is induced in the ectoderm by signals from the dorsal mesoderm. In the extensively studied species Xenopus laevis, such signals are believed to proceed along two alternate pathways, defined as vertical and planar induction. We have studied the relative importance of these pathways in Rana pipiens. In the embryo of this frog, dorsal mesoderm involution can be diverted from its normal course by injection of peptides that inhibit interaction of fibronectin with its receptor. In such embryos, dorsal mesoderm failed to migrate across the blastocoel roof but moved bilaterally along the equator, leading to the formation of two notochords. Neural tissue differentiation occurred in close association with each notochord, but no neural tissue formed along the dorsal midline as might have been predicted by a predominantly planar induction model. While in X. laevis planar induction has been reported to be a major pathway in neuralizing the ecoderm, the results presented here indicate that vertical induction predominates in initiating neural development in R. pipiens embryos.

Amino Acid Sequence↗
PubMed1994

Expression patterns of the murine LIM class homeobox gene lim1 in the developing brain and excretory system.

We report the cloning, sequence analysis, and developmental expression pattern of lim1, a member of the LIM class homeobox gene family in the mouse. lim1 cDNA encodes a predicted 406 amino acid protein that is 93% identical with the product of the Xenopus LIM class homeobox gene Xlim1. We have characterized lim1 expression from day 8.5 post coitum onward. Northern blot analysis of RNA transcripts indicates that lim1 is expressed both during embryogenesis and in the adult brain. Analysis by whole-mount and section in situ hybridization shows lim1 expression in the central nervous system from the telencephalon through the spinal cord and in the developing excretory system including pronephric region, mesonephros, nephric duct, and metanephros. In the metanephros, lim1 is strongly expressed in renal vesicles and S-shaped bodies, and transcripts are also detected in the ureteric branches.

Amino Acid Sequence↗
PubMed1994

A fate map for the 32-cell stage of Rana pipiens.

A fate map of the progeny derived from all blastomeres of the 32-cell stage embryo of the leopard frog Rana pipiens has been generated. Embryos presenting regular cleavages were injected into two pairs of blastomeres with fluorescein- and Texas red-lysine dextran. By stage 21, embryos were sectioned and the tissue distribution of labeled clones was determined. The results of 93 clones were pooled to give a fate map which represents the derivation of each tissue from the different blastomeres of the 32-cell embryo. The results show that all blastomeres give rise to multiple tissues and all tissues are derived from at least two, and usually more, pairs of blastomeres. Although there is a general tendency for ectoderm to derive from the animal hemisphere, endoderm from the vegetal hemisphere, and mesoderm from the equatorial region, the boundaries between germ layers are not sharply defined at the 32-cell stage but rather appear as a series of overlapping zones. The fate map of R. pipiens is quite similar to that of Xenopus laevis but differs in some details that are discussed. As in all vertebrates, the R. pipiens fate map is not fully deterministic but nevertheless has predictive value in that tissues are populated by the progeny of the same blastomeres in different embryos.

Animals↗