PubMed Health⌕ Search

Biomedical subjects

S L Ang

Publications and source records attributed to S L Ang.

33 records · Page 2Linked to original sources
PubMed1995

The mouse fkh-2 gene. Implications for notochord, foregut, and midbrain regionalization.

The "winged helix" or "forkhead" transcription factors comprise a large gene family whose members are defined by a common 100-amino acid DNA binding domain. Here we describe the structure and expression of the mouse fkh-2 gene, which encodes a protein of 48 kDa with high similarity to other winged helix transcription factors within the DNA binding region, but unique potential transactivation domains. The gene is encoded by a single exon and is expressed in headfold stage embryos in the notochord, the anterior neuroectoderm, and a few cells of the definite endoderm. This expression becomes restricted to the anteriormost portions of the invaginating foregut and the developing midbrain. From day 11.5 of gestation onward, fkh-2 transcripts are restricted to the midbrain and become progressively localized to the red nuclei as the sole site of expression. The fkh-2 gene maps to chromosome 19B and is a candidate gene for the mouse mutation mdf (muscle-deficient) which is characterized by nervous tremors and degeneration of the hindlimb muscles. Although the expression patterns of the fkh-2 gene and another winged helix protein, HNF-3 beta, are overlapping in early stages of gestation and although the promoter of the fkh-2 gene contains a HNF-3 binding site, we demonstrate that the activation of the fkh-2 gene is independent of HNF-3 beta.

Amino Acid Sequence↗
PubMed1995

Targeted disruption of mammalian hairy and Enhancer of split homolog-1 (HES-1) leads to up-regulation of neural helix-loop-helix factors, premature neurogenesis, and severe neural tube defects.

Mammalian hairy and Enhancer of split homolog-1 (HES-1) encodes a helix-loop-helix (HLH) factor that is thought to act as a negative regulator of neurogenesis. To directly investigate the functions of HES-1 in mammalian embryogenesis, we performed a targeted disruption of the HES-1 locus. Mice homozygous for the mutation exhibited severe neurulation defects and died during gestation or just after birth. In the developing brain of HES-1-null embryos, expression of the neural differentiation factor Mash-1 and other neural HLH factors was up-regulated and postmitotic neurons appeared prematurely. These results suggest that HES-1 normally controls the proper timing of neurogenesis and regulates neural tube morphogenesis.

Animals↗
PubMed1994

HNF-3 beta is essential for node and notochord formation in mouse development.

HNF-3 beta, a member of the HNF-3/fork head family of transcription factors, is expressed in the node, notochord, floor plate, and gut in mouse embryos. A null mutation of this gene leads to embryonic lethality. The primary defect of HNF-3 beta -/- embryos is an absence of organized node and notochord formation, which leads to secondary defects in dorsal-ventral patterning of the neural tube. In contrast, patterning along the anterior-posterior axis was surprisingly little affected. Although HNF-3 beta is required for node and notochord formation, some organizer activity persists in the absence of these structures. HNF-3 beta is not required for the development of definitive endoderm cells, but foregut morphogenesis is severely affected in HNF-3 beta -/- embryos.

Animals↗
PubMed1994

Positive and negative signals from mesoderm regulate the expression of mouse Otx2 in ectoderm explants.

Otx2, a mouse homolog of the Drosophila orthodenticle gene, is first widely expressed in the epiblast but becomes progressively restricted to the anterior third of the embryo by the headfold stage. This progressive restriction correlates with the anterior migration of mesoderm in the embryo, suggesting that interactions with mesoderm may be involved in setting up the anterior domain of Otx2 expression in vivo. Using explant-recombination assays, we have obtained evidence that a positive signal from anterior mesendoderm is required to stabilize expression of Otx2 in vivo, whereas a negative signal from the later-forming posterior mesendoderm represses Otx2 expression in the posterior part of the embryo. We have also found that exogenous retinoic acid can mimic the effect of this negative signal and reduces the anterior domain of Otx2 expression.

Animals↗
PubMed1993

Anterior mesendoderm induces mouse Engrailed genes in explant cultures.

We have developed germ layer explant culture assays to study the role of mesoderm in anterior-posterior (A-P) patterning of the mouse neural plate. Using isolated explants of ectodermal tissue alone, we have demonstrated that the expression of Engrailed-1 (En-1) and En-2 genes in ectoderm is independent of mesoderm by the mid- to late streak stage, at least 12 hours before their onset of expression in the neural tube in vivo at the early somite stage. In recombination explants, anterior mesendoderm from headfold stage embryos induces the expression of En-1 and En-2 in pre- to early streak ectoderm and in posterior ectoderm from headfold stage embryos. In contrast, posterior mesendoderm from embryos of the same stage does not induce En genes in pre- to early streak ectoderm but is able to induce expression of a general neural marker, neurofilament 160 x 10(3) M(r). These results provide the first direct evidence for a role of mesendoderm in induction and regionalization of neural tissue in mouse.

Animals↗
PubMed1993

The formation and maintenance of the definitive endoderm lineage in the mouse: involvement of HNF3/forkhead proteins.

Little is known about genes that govern the development of the definitive endoderm in mammals; this germ layer gives rise to the intestinal epithelium and various other cell types, such as hepatocytes, derived from the gut. The discovery that the rat hepatocyte transcription factor HNF3 is similar to the Drosophila forkhead gene, which plays a critical role in gut development in the fly, led us to isolate genes containing the HNF3/forkhead (HFH) domain that are expressed in mouse endoderm development. We recovered mouse HNF3 beta from an embryo cDNA library and found that the gene is first expressed in the anterior portion of the primitive streak at the onset of gastrulation, in a region where definitive endoderm first arises. Its expression persists in axial structures derived from the mouse equivalent of Hensen's node, namely definitive endoderm and notochord, and in the ventral region of the developing neural tube. Expression of the highly related gene, HNF3 alpha, appears to initiate later than HNF3 beta and is first seen in midline endoderm cells. Expression subsequently appears in notochord, ventral neural tube, and gut endoderm in patterns similar to HNF3 beta. Microscale DNA binding assays show that HNF3 proteins are detectable in the midgut at 9.5 days p.c. At later stages HNF3 mRNAs and protein are expressed strongly in endoderm-derived tissues such as the liver. HNF3 is also the only known hepatocyte-enriched transcription factor present in a highly de-differentiated liver cell line that retains the capacity to redifferentiate to the hepatic phenotype. Taken together, these studies suggest that HNF3 alpha and HNF3 beta are involved in both the initiation and maintenance of the endodermal lineage. We also discovered a novel HFH-containing gene, HFH-E5.1, that is expressed transiently in posterior ectoderm and mesoderm at the primitive streak stage, and later predominantly in the neural tube. HFH-E5.1 is highly similar in structure and expression profile to the Drosophila HFH gene FD4, suggesting that HFH family members have different, evolutionarily conserved roles in development.

Amino Acid Sequence↗
PubMed1992

Regional localization of the human G protein alpha i2 (GNAI2) gene: assignment to 3p21 and a related sequence (GNAI2L) to 12p12-p13.

Gi alpha proteins, members of the G protein signal transduction family, include a small number of polypeptides: Gi alpha 1 (GNAI1), Gi alpha 2 (GNAI2), and Gi alpha 3 (GNAI3). A cDNA for the human GNAI2 gene has been isolated from a human T-cell library and is mapped by chromosomal in situ hybridization to the short arm of chromosome 3 at 3p21. A related sequence, GNAI2L, is mapped by in situ hybridization to the short arm of chromosome 12 at p12-p13. These mapping results are further supported by amplification of GNAI2-specific sequences in a monochromosomal human/rodent somatic cell hybrid containing only human chromosome 3. Of note, these assignments are to chromosome regions in which other G proteins reside. Localization of GNAI2 to 3p21 is of great interest as this region of the short arm of chromosome 3 is frequently involved in rearrangements in various human tumors.

Animals↗
PubMed1990

Gamma-delta T cells in Chediak-Higashi syndrome.

Lymphocytes from children with Chediak-Higashi syndrome (CHS) have impaired natural killer (NK) activity and lack antibody-dependent cell-mediated cytotoxicity. Study of T cells bearing an alternate T cell receptor comprised of gamma- and delta-chains, which typically demonstrate NK activity in vitro, was undertaken in CHS patients. We demonstrate that the cellular machinery for lysis of target cells in vitro is present in CHS-derived gamma delta T cell clones. We also show that the proportion of gamma delta T cells among peripheral blood mononuclear cells is significantly increased in CHS, the first example of a specific immunodeficiency disorder with a relative expansion of these T cells.

Cell Line↗
PubMed1988

Identification of cDNA encoding an additional alpha subunit of a human GTP-binding protein: expression of three alpha i subtypes in human tissues and cell lines.

The guanine nucleotide-binding proteins (G proteins), which mediate hormonal regulation of many membrane functions, are composed of alpha, beta, and gamma subunits. We have cloned and characterized cDNA from a human T-cell library encoding a form of alpha i that is different from the human alpha i subtypes previously reported [Didsbury, J. R., Ho, Y.-S. & Snyderman, R. (1987) FEBS Lett. 211, 160-164 and Bray, P., Carter, A., Guo, V., Puckett, C., Kamholz, J., Spiegel, A. & Nirenberg, M. (1987) Proc. Natl. Acad. Sci. USA 84, 5115-5119]. alpha i is the alpha subunit of a class of G proteins that inhibits adenylate cyclase and regulates other enzymes and ion channels. This cDNA encodes a polypeptide of 354 amino acids and is assigned to encode the alpha i-3 subtype of G proteins on the basis of its similarity to other alpha i-like cDNAs and the presence of a predicted site for ADP ribosylation by pertussis toxin. We have determined the expression of mRNA for this and two other subtypes of human alpha i (alpha i-1 and alpha i-2) in a variety of human fetal tissues and in human cell lines. All three alpha i subtypes were present in the tissues tested. However, analysis of individual cell types reveals specificity of alpha i-1 expression. mRNA for alpha i-1 is absent in T cells, B cells, and monocytes but is present in other cell lines. The finding of differential expression of alpha i-1 genes may permit characterization of distinct physiological roles for this alpha i subunit. mRNA for alpha i-2 and alpha i-3 was found in all the primary and transformed cell lines tested. Thus, some cells contain all three alpha i subtypes. This observation raises the question of how cells prevent cross talk among receptors that are coupled to effectors through such similar alpha proteins.

Amino Acid Sequence↗
PubMed1987

Functional gamma chain-associated T cell receptors on cerebrospinal fluid-derived natural killer-like T cell clones.

We have derived 33 independent T cell clones from the cerebrospinal fluid (CSF) of a patient with subacute sclerosing panencephalitis using a single T cell cloning method. 6% (2 of 33) of these clones express the T cell receptor gamma (TCR-gamma) protein and are called CSF TCR-gamma clones. Phenotypic analyses of the CSF TCR-gamma clones indicate that they are WT-31-, CD3+, CD4-, and CD8-. The TCR-gamma protein exists on the cell surface as part of an 85-kD disulphide-linked dimer noncovalently associated with the CD3 polypeptides. The CSF TCR-gamma clones have NK-like activity that can be inhibited by anti-CD3 mAbs. Both CSF TCR-gamma clones proliferated in response to anti-CD3 mAbs coupled to Sepharose beads and/or IL-2. Furthermore, stimulation of one of these clones with anti-CD3 mAbs results in a rapid rise in intracellular calcium. These data suggest that T cells bearing the CD3-TCR-gamma protein complex are functional and play a role in the human immune response.

Cerebrospinal Fluid↗
PubMed1987

Two types of gamma T cell receptors expressed by T cell acute lymphoblastic leukemias.

CD3+ cells, isolated from peripheral blood of two patients with T cell acute lymphoblastic leukemia (T-ALL), did not react with the monoclonal antibody WT31, which is thought to recognize a framework determinant on the conventional T cell receptor (TcR), consisting of disulfide-linked alpha and beta chains. The T-ALL cells of neither patient synthesized TcR alpha mRNA; the cells of patient DD contained only truncated (D-J) TcR beta mRNA, while the cells of patient HZ contained truncated as well as mature (V-D-J) TcR beta mRNA. The leukemic cells of both patients made TcR gamma mRNA. At the cell surface, the T-ALL cells of patient DD expressed a CD3-associated disulfide-linked dimer, which contained the TcR gamma protein. On the leukemic cells of patient HZ the TcR gamma protein was present as a 41-44-kDa CD3-associated subunit in a noncovalently linked form. The TcR gamma genes in the T-ALL cells of patient DD were rearranged exclusively to the C gamma 1 locus, while in the T-ALL cells of patient HZ both C gamma 1 alleles were deleted and rearrangement to the C gamma 2 locus had occurred. The C gamma 1 gene segment, just like the TcR alpha and TcR beta gene segments, contains a cysteine codon in its second exon. This cysteine residue is involved in the formation of the interchain disulfide bond. The human C gamma 2 gene segment, however, does not contain a cysteine codon in its second exon. The absence of the cysteine residue in C gamma 2 encoded TcR gamma chains explains the lack of an interchain disulfide bond in the TcR on the T-ALL cells of patient HZ. The TcR gene configuration, as well as the expression of model for T cell differentiation in which the TcR gamma gene rearranges first to the C gamma 1 locus prior to or coinciding with D-J joining of the TcR beta gene, followed by rearrangement to the C gamma 2 locus and V-D-J joining of the TcR beta gene.

Antigens, Differentiation, T-Lymphocyte↗
PubMedDate not supplied

A T-cell receptor gamma/CD3 complex found on cloned functional lymphocytes.

Cloned blood lymphocytes that do not express the alpha- and beta-chains of the T-cell receptor show MHC-unrestricted cytotoxicity. These cells carry the gamma-protein, disulphide-linked either to another molecule or to itself, and associated with the CD3 complex. These observations may help to solve the mystery posed by the discovery of the gamma gene.

Antigens, Differentiation, T-Lymphocyte↗
PubMedDate not supplied

Two forms of the T-cell receptor gamma protein found on peripheral blood cytotoxic T lymphocytes.

The T-cell receptor (TCR) gamma polypeptide is expressed associated with CD3 (T3) on the surface of normal human peripheral blood lymphocytes. These cells function as non-MHC-restricted cytotoxic T lymphocytes (CTL)and thus may play an important role in host immune defence. The TCR gamma polypeptide occurs as a dimer in at least two molecular forms based on the absence or presence of disulphide linkage. These forms use TCR gamma polypeptides with strikingly different peptide backbone sizes.

Antigens, Differentiation, T-Lymphocyte↗
PubMedDate not supplied

Characterization of an expressed CD3-associated Ti gamma-chain reveals C gamma domain polymorphism.

The majority of human T cells express an antigen receptor consisting of a disulphide-linked heterodimer (Ti) of relative molecular mass 80,000-90,000 (Mr 80-90K) which is noncovalently associated with a set of at least three proteins of Mr 20-28K termed CD3 (Leu4, T3). Whereas both chains of Ti, an acidic alpha-chain of Mr 48-54K and a more basic beta-chain of Mr 40-44K, contain variable and constant region domains, the component peptides of CD3 are invariant. Several laboratories have more recently reported the expression of CD3 in association with a novel protein. On the surface of long-term T-cell lines and one thymocyte clone this novel structure consists of a 40K protein noncovalently linked to a 55 or 62K protein identified as the protein product of the Ti gamma-chain gene, a T-cell specific gene which like the Ti alpha- and Ti beta-chain genes undergoes rearrangement of variable (V) and joining (J) region gene segments. On the human T-cell leukaemic line PEER we have detected only a single 55K glycoprotein associated with CD3. We here demonstrate that an anti-Ti gamma-peptide antiserum reacts with the 55K CD3-associated protein on PEER. Most previously described human Ti gamma-chain complementary DNA clones encode the products of non-functional rearrangements. One of the Ti gamma cDNAs isolated from PEER, however, represents a functional rearrangement reported for the first time in a cell which expresses a Ti gamma-chain protein product on the cell surface. Interestingly, a 48-base-pair (bp) sequence in the constant (C) region domain of this functional Ti gamma-chain cDNA is triplicated in PEER and duplicated in other cDNAs isolated from PEER and other cell lines.

Antigens, Differentiation, T-Lymphocyte↗