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G W Litman

Publications and source records attributed to G W Litman.

At least 55 records · Page 3Linked to original sources
PubMed1995

Generation of immunoglobulin light chain gene diversity in Raja erinacea is not associated with somatic rearrangement, an exception to a central paradigm of B cell immunity.

In all vertebrate species examined to date, rearrangement and somatic modification of gene segmental elements that encode portions of the antigen-combining sites of immunoglobulins are integral components of the generation of antibody diversity. In the phylogenetically primitive cartilaginous fishes, gene segments encoding immunoglobulin heavy and light chain loci are arranged in multiple clusters, in which segmental elements are separated by only 300-400 bp. In some cases, segmental elements are joined in the germline of nonlymphoid cells (joined genes). Both genomic library screening and direct amplification of genomic DNA have been used to characterize at least 89 different type I light chain gene clusters in the skate, Raja. Analyses of predicted nucleotide sequences and predicted peptide structures are consistent with the distribution of genes into different sequence groups. Predicted amino acid sequence differences are preferentially distributed in complementarity-determining versus framework regions, and replacement-type substitutions exceed neutral substitutions. When specific germline sequences are related to the sequences of individual cDNAs, it is apparent that the joined genes are expressed and are potentially somatically mutated. No evidence was found for the presence of any type I light chain gene in Raja that is not germline joined. The type I light chain gene clusters in Raja appear to represent a novel gene system in which combinatorial and junctional diversity are absent.

Amino Acid Sequence↗
PubMed1995

Predominance of sterile immunoglobulin transcripts in a female phenotypically resembling Bruton's agammaglobulinemia.

The transcription pattern of the heavy chain immunoglobulin gene locus was analyzed in a 6-month-old female with agammaglobulinemia characterized by the absence of mature B cells in peripheral blood, arrested B cell development in the bone marrow and lack of germinal center development. DNA sequencing provided no evidence of mutations within the coding region of the Bruton's tyrosine kinase gene. Polymerase chain reaction-generated cDNA libraries from blood and bone marrow were screened initially using JH and CH oligodeoxynucleotide probes and VH family-specific probes. Only 10% of the transcripts constituted mature VDJC mu recombinations. Ninety percent of the cDNA were sterile immunoglobulin transcripts comprised of: DJC mu (DH-JHC mu), JC mu (JH-C mu), EC mu (enhancer spliced to C mu), SC mu and IC mu [corresponding to switch (S) and intron (I) regions spliced to C mu]. In the mature immunoglobulin transcripts, VH use indicated germline expression with little evidence of somatic mutation. All cDNA were of the C mu type. Different D segments, D-D joining events and unknown D-like elements were noted in the DJC mu and VDJC mu transcripts. This pattern of immunoglobulin rearrangements, along with the phenotypic cell surface antigen characteristics (CD19-), suggest that an earlier arrest in B cell development than is characteristic of Bruton's X-linked agammaglobulinemia has occurred in this patient.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1995

Identification and characterization of T-cell antigen receptor-related genes in phylogenetically diverse vertebrate species.

Characterization of the structure, multiplicity, organization, and cell lineage-specific expression of T-cell receptor (TCR) genes of nonmammalian vertebrate species is central to the understanding of the evolutionary origins of rearranging genes of the vertebrate immune system. We recently described a polymerase chain reaction (PCR) strategy that relies on short sequence similarities shared by nearly all vertebrate TCR and immunoglobulin (Ig) variable (V) regions and have used this approach to isolate a TCR beta (TCRB) homolog from a cartilaginous fish. Using these short PCR products as probes in spleen cDNA and genomic libraries, we were able to isolate a variety of unique TCR and TCR-like genes. Here we report the identification and characterization of a chicken TCR gamma (TCRG) homolog, apparent Xenopus and pufferfish TCR alpha (TCRA) homologs, and two horned shark TCR delta (TCRD)-like genes. In addition, we have identified what could be a novel representative of the Ig gene superfamily in the pufferfish. This method of using short, minimally degenerate PCR primers should speed progress in the phylogenetic investigations of the TCR and related genes and lend important insights into both the origins and functions of these unique gene systems.

Amino Acid Sequence↗
PubMed1994

T-cell receptor gene homologs are present in the most primitive jawed vertebrates.

The phylogenetic origins of T-cell immunity and T-cell antigen receptor (TCR) genes have not been established. A PCR approach using short, minimally degenerate oligodeoxynucleotide primers complementing conserved variable region segments amplifies TCR-like products from the genomic DNA of Heterodontus francisci (horned shark), a representative phylogenetically primitive cartilaginous fish. One of these products has been used as a probe to screen a Heterodontus spleen cDNA library and a clone was identified that is most related at the nucleotide sequence and predicted peptide levels to higher vertebrate TCR beta-chain genes. Genomic analyses of the TCR homologs indicate that recombining variable and joining region segments as well as constant region exons are encoded by extensive gene families, organized in the multicluster form, characteristic of both the immunoglobulin heavy- and light-chain gene loci in the cartilaginous fishes. Greater numbers of homologous products were identified when a probe complementing the putative constant region of the TCR homolog was used to screen the same cDNA library. A high degree of intergenic variation is associated with the putative variable region segments of these isolates. Direct evidence is presented for TCR-like genes, which presumably are associated with T-cell function, at the earliest stages in the phylogenetic emergence of jawed vertebrates.

Amino Acid Sequence↗
PubMed1994

Genomic organization and structure of Bruton agammaglobulinemia tyrosine kinase: localization of mutations associated with varied clinical presentations and course in X chromosome-linked agammaglobulinemia.

X chromosome-linked agammaglobulinemia is a life-threatening disease that involves a failure in normal development of B lymphocytes and is associated with missense mutations in BTK, a gene encoding a cytoplasmic tyrosine kinase (Bruton agammaglobulinemia tyrosine kinase, EC 2.7.1.112), a member of the Tec family of protein-tyrosine kinases. The genomic organization has been determined by using conventional restriction fragment mapping, extended DNA sequencing, and PCR fragment-sizing approaches. The DNA sequences of the 18 coding exons composing BTK and their flanking-region sequences are reported; an additional exon(s) encodes a 5' untranslated segment. Single-base-pair substitutions and 4-nt deletions resulted in amino acid replacement, premature termination, frameshift, and exon deletion in a group of X chromosome-linked agammaglobulinemia patients exhibiting different clinical presentations and courses. The nature of the mutations is interpreted in terms of the genomic organization of the BTK gene and the disease course in individual patients. Several examples are found in which the same mutation occurs in unrelated patients, and one of these mutations occurs at the same codon that is substituted in the murine form of BTK, resulting in X chromosome-linked immunodeficiency disease. Considerable variation in presentation and disease course in X chromosome-linked agammaglobulinemia appears associated with the nature and position of different missense mutations.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1994

Immunoglobulin light chain class multiplicity and alternative organizational forms in early vertebrate phylogeny.

The prototypic chondrichthyan immunoglobulin (Ig) light chain type (type I) isolated from Heterodontus francisci (horned shark) has a clustered organization in which variable (V), joining (J), and constant (C) elements are in relatively close linkage (V-J-C). Using a polymerase chain reaction-based approach on a light chain peptide sequence from the holocephalan, Hydrolagus colliei (spotted ratfish), it was possible to isolate members of a second light chain gene family. A probe to this light chain (type II) detects homologs in two orders of elasmobranchs, Heterodontus, a galeomorph and Raja erinacea (little skate), a batoid, suggesting that this light chain type may be present throughout the cartilaginous fishes. In all cases, V, J, and C regions of the type II gene are arranged in closely linked clusters typical of all known Ig genes in cartilaginous fishes. All representatives of this type II gene family are joined in the germline. A third (kappa-like) light chain type from Heterodontus is described. These findings establish that a degree of light chain class complexity comparable to that of the mammals is present in the most phylogenetically distant extant jawed vertebrates and that the phenomenon of germline-joined (pre-rearranged) genes, described originally in the heavy chain genes of cartilaginous fishes, extends to light chain genes.

Amino Acid Sequence↗
PubMed1994

TXK, a novel human tyrosine kinase expressed in T cells shares sequence identity with Tec family kinases and maps to 4p12.

A gene for a novel, putative cytoplasmic tyrosine kinase, TXK has been isolated from a human peripheral blood cDNA library. The complete nucleotide sequence of the cDNA indicates that it is related most closely to EMT, a tyrosine kinase of T cells and to the B-cell tyrosine kinase Btk, which is mutated in X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency disease (XID) in mouse. TXK, like BTK, is a member of the Tec sub-family of Src-type (non-receptor) tyrosine kinases. Like similar Tec sub-family members, and unlike the other Src kinases, TXK lacks both the N-terminal myristylation signal and the C-terminal regulatory tyrosine. TXK expression is detected primarily in T cells and some myeloid cell lines but not in a number of other cell types. TXK shares 60% amino acid homology with EMT and 57% with BTK over the SH3, SH2 (Src-homology) and catalytic domains but unlike BTK, EMT and tec, it lacks Gap 1 homology and steroid hormone receptor homology in the N-terminal region. Genomic clones containing TXK have been isolated and hybridize to chromosome position 4p12.

Amino Acid Sequence↗
PubMed1993

Somatic variation precedes extensive diversification of germline sequences and combinatorial joining in the evolution of immunoglobulin heavy chain diversity.

In Heterodontus, a phylogenetically primitive shark species, the variable (VH), diversity (DH), joining (JH) segments, and constant (CH) exons are organized in individual approximately 18-20-kb "clusters." A single large VH family with > 90% nucleic acid homology and a monotypic second gene family are identified by extensive screening of a genomic DNA library. Little variation in the nucleotide sequences of DH segments from different germline gene clusters is evident, suggesting that the early role for DH was in promoting junctional diversity rather than contributing unique coding specificities. A gene-specific oligodeoxynucleotide screening method was used to relate specific transcription products (cDNAs) to individual gene clusters and showed that gene rearrangements are intra- rather than intercluster. This provides further evidence for restricted diversity in the immunoglobulin heavy chain of Heterodontus, from which it is inferred that combinatorial diversity is a more recently acquired means for generating diversity. The observed differences between cDNA sequences selected and the sequences of segmental elements derived from conventional genomic libraries as well as from VH segment-specific libraries generated by direct PCR amplification of genomic DNA indicate that the VH repertoire is diversified by both junctional diversity and somatic mutation. Taken together, these findings suggest a heretofore unrecognized contribution of somatic variation that preceded both extensive diversification of the germline repertoire and the combinatorial joining process in the evolution of humoral immunity.

Animals↗
PubMed1993

VH gene organization in a relict species, the coelacanth Latimeria chalumnae: evolutionary implications.

The living coelacanth Latimeria chalumnae is a relict species whose higher-level phylogenetic relationships have not been resolved clearly by traditional systematic approaches. Previous studies show that major differences in immunoglobulin gene structure and organization typify different phylogenetic lineages. To date, mammalian-, avian-, and elasmobranch-type gene organizations have been identified in representatives of these different phylads. A fourth form or organization is found in Latimeria, which possesses immunoglobulin heavy-chain variable region (VH) elements separated by approximately 190 nucleotides from diversity (D) elements. Adjacency of VH and D elements is characteristic of the elasmobranch "clustered" arrangement, although many other features of coelacanth VH gene organization and structure are more similar to those of bony fishes and tetrapods. These observations strongly support a phylogenetic hypothesis in which Latimeria occupies a sister-group relationship with teleosts and tetrapods.

Amino Acid Sequence↗
PubMed1993

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire.

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.

Animals↗
PubMed1991

The genomic organization of immunoglobulin VH genes in Xenopus laevis shows evidence for interspersion of families.

The complete genomic sequences of Xenopus laevis immunoglobulin heavy chain variable region (VH) genes comprising families IV-XI are reported. Using VH family-specific probes, linkage relationships for Xenopus VHI-VHXI have been determined. With the possible exceptions of VHIII and VHVII, Xenopus VH genes appear to be interspersed. When from two to five VH segments are identified in individual clones, the elements are found to be in the same relative transcriptional orientation. Although the relationships of promoter sequences, including the regulatory octamer, resemble those seen in other vertebrate VH genes, several Xenopus VH families are associated with additional 5' octamer sequences and octamer-like motifs. The similarities between the genomic organization of VH genes in Xenopus and higher vertebrates, indicate an early phylogenetic emergence of the mammalian-type of gene organization and regulation.

Animals↗
PubMed1991

A serum heterodimer from hagfish (Eptatretus stoutii) exhibits structural similarity and partial sequence identity with immunoglobulin.

We have isolated, characterized, and partially sequenced immunoglobulin from the most primitive extant nonvertebrate craniate, the hagfish, a jawless fish that may have diverged from the vertebrate lineage more than 500 million years ago. The 160-kDa protein, which is a minor serum component, is composed of two different heavy chains of 69 and 74 kDa and a light chain of 29 kDa and resembles known immunoglobulin on the basis of an equimolar ratio of heavy and light chains, N-linked glycosylation of heavy chains, presence of intra- and interchain disulfide bonds, and polydispersity of each peptide chain. High molecular mass (polymeric) as well as low molecular mass (monomeric) forms were isolated from serum. The hagfish immunoglobulin is unique in that each heterodimer is composed of two different heavy chains and two light chains. The partial peptide maps and amino acid compositions of the two heavy chains differ; the chains do not crossreact immunologically. Slight crossreactivity of the 74-kDa heavy chain with antisera against purified shark immunoglobulin and some conservation of amino acid sequences, including those surrounding a cysteine, suggest that the isolated protein is an immunoglobulin.

Amino Acid Sequence↗