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G W Litman

Publications and source records attributed to G W Litman.

At least 73 records · Page 4Linked to original sources
PubMed1990

Two distinct immunoglobulin heavy chain isotypes in a primitive, cartilaginous fish, Raja erinacea.

Immunoglobulin heavy chain genes in Raja erinacea (little skate) are organized in clusters consisting of VH, DH, JH segments and CH exons (1). An immunoglobulin heavy chain mu-like isotype that exhibits 61-91% nucleotide sequence identity in coding segments to the Heterodontus francisci (horned shark) mu-type immunoglobulin is described. The overall length of the mu-type clusters is approximately 16 kb; transmembrane exons (TM1 and TM2) are located 3 to CH exon 4 (CH4). In three of four TM-containing genomic clones, a significant deletion is present in TM1. A second isotype of Raja immunoglobulin heavy chain genes has been detected by screening a spleen cDNA library with homologous Raja VH- and CH1-specific probes complementing the respective regions of the mu-like isotype. Weak hybridization with VH-specific probes and no discernable hybridization with C mu-specific probes were considered presumptive evidence for a second immunoglobulin isotype that nominally is designated as X-type. The Vx region of the X-type cDNA is approximately 60% identical at the nucleotide (nt) level to other Raja VH segments and thus represents a second VH family. Putative Dx and Jx sequences also have been identified. The constant region of the X-type immunoglobulin heavy chain gene consists of two characteristic immunoglobulin domains and a cysteine-rich carboxy terminal segment that are only partially homologous with the mu-like isotype. Genomic Southern blotting indicates that the V and C segments of both immunoglobulin heavy chain isotypes are encoded by complex multigene families. Vx- and different Cx-specific probes hybridize to different length transcripts in northern blot analyses of Raja spleen RNA suggesting that the regulation of expression of the X-type genes may involve differential RNA processing.

Amino Acid Sequence↗
PubMed1990

Eleven distinct VH gene families and additional patterns of sequence variation suggest a high degree of immunoglobulin gene complexity in a lower vertebrate, Xenopus laevis.

Lower vertebrate species, including Xenopus laevis, exhibit restricted antibody diversity relative to higher vertebrates. We have analyzed more than 180 VH gene-containing recombinant clones from an unamplified spleen cDNA library by selective sequencing of JH and CH positive clones following iterative hybridization screening with family-specific VH probes, 11 unique families of VH genes, each associated with a unique genomic Southern blot hybridization pattern, are described and compared. Considerable variation in the number of hybridizing components detected by each probe is evident. The nucleotide sequence difference between VH families is as great as, if not more than, that reported in other systems, including representatives of the mammalian, avian, and elasmobranch lineages. Some Xenopus Ig gene families encode alternative amino acids at positions that are otherwise invariant or very rarely substituted in known Igs. Furthermore, variations in complementarity determining region sequences among members of the same gene family and high degrees of DH and JH region complexity are described, suggesting that in at least this lower vertebrate species, the diversity of expressed Ig VH genes is not restricted.

Amino Acid Sequence↗
PubMed1990

Immunoglobulin heavy chain gene organization and complexity in the skate, Raja erinacea.

Immunoglobulin heavy chain genes from Raja erinacea have been isolated by cross hybridization with probes derived from the immunoglobulin genes of Heterodontus francisci (horned shark), a representative of a different elasmobranch order. Heavy chain variable (VH), diversity (DH) and joining (JH) segments are linked closely to constant region (CH) exons, as has been described in another elasmobranch. The nucleotide sequence homology of VH gene segments within Raja and between different elasmobranch species is high, suggesting that members of this phylogenetic subclass may share one VH family. The organization of immunoglobulin genes segments is diverse; both VD-J and VD-DJ joined genes have been detected in the genome of non-lymphoid cells. JH segment sequence diversity is high, in contrast to that seen in a related elasmobranch. These data suggest that the clustered V-D-J-C form of immunoglobulin heavy chain organization, including germline joined components, may occur in all subclasses of elasmobranchs. While variation in VH gene structure is limited, gene organization appears to be diverse.

Amino Acid Sequence↗
PubMed1990

Complete nucleotide sequence of an immunoglobulin heavy-chain gene and analysis of immunoglobulin gene organization in a primitive teleost species.

The immunoglobulin heavy-chain variable region (VH) locus in a phylogenetically primitive teleost (Elops saurus) has been characterized by a strategy that relied initially on cross-hybridization between genomic VH segments and a murine VH probe. Using a homologous (Elops) VH probe and DNA sequencing, this gene family has been shown to be complex and to contain overt pseudogenes. A homologous probe also has been used to isolate a full copy length cDNA containing constant (CH) as well as joining (JH) and VH regions. Genomic analyses using CH-, JH-, and VH-specific probes have demonstrated the presence of only a single hybridizing CH and several JH elements. JH-CH linkage is less than or equal to 3.6 kilobases (kb) and VH-CH linkage is less than or equal to 100 kb, as estimated by field-inversion gel electrophoresis. An additional VH family sharing less than 50% nucleotide identity with the prototype Elops VH sequence is described. Taken together, these results suggest that the immunoglobulin VH locus in a comparatively primitive teleost resembles the VH locus in mammals, but not that found in the more phylogenetically distant elasmobranchs. The evolutionary radiations of cartilaginous and bony fishes are associated with a dramatic change in the organization and, presumably, regulation of immunoglobulin genes. The origins of the modern VH gene locus can be traced to the primitive teleost fishes.

Amino Acid Sequence↗
PubMed1989

Genomic organization and sequences of immunoglobulin light chain genes in a primitive vertebrate suggest coevolution of immunoglobulin gene organization.

The genomic organization and sequence of immunoglobulin light chain genes in Heterodontus francisci (horned shark), a phylogenetically primitive vertebrate, have been characterized. Light chain variable (VL) and joining (JI) segments are separated by 380 nucleotides and together with the single constant region exon (CI), occupy less than 2.7 kb, the closest linkage described thus far for a rearranging gene system. The VL segment is flanked by a characteristic recombination signal sequence possessing a 12 nucleotide spacer; the recombination signal sequence flanking the JL segment is 23 nucleotides. The VL genes, unlike heavy chain genes, possess a typical upstream regulatory octamer as well as conserved enhancer core sequences in the intervening sequence separating JL and CL. Restriction mapping and genomic Southern blotting are consistent with the presence of multiple light chain gene clusters. There appear to be considerably fewer light than heavy chain genes. Heavy and light chain clusters show no evidence of genomic linkage using field inversion gel electrophoresis. The findings of major differences in the organization and functional rearrangement properties of immunoglobulin genes in species representing different levels of vertebrate evolution, but consistent similarity in the organization of heavy and light chain genes within a species, suggests that these systems may be coevolving.

Amino Acid Sequence↗
PubMed1989

Evolutionary immunobiology.

Identifying the evolutionary origin of inducible, specific immune recognition represents a major objective in developmental immunology. In order to address this issue from an overall phylogenetic perspective, major studies of cellular and humoral immune function are being undertaken using lower vertebrate and invertebrate models. Here, C. Reinisch and G. Litman discuss the application of new technologies, particularly molecular genetic approaches, that is providing important new insights into the genetic mechanisms that have influenced the evolutionary diversification of immunological function.

Animals↗
PubMed1989

Complete nucleotide sequence of primitive vertebrate immunoglobulin light chain genes.

Antibody to Heterodontus francisci (horned shark) immunoglobulin light chain was used to screen a spleen cDNA expression library, and recombinant clones encoding light chain genes were isolated. The complete sequences of the mature coding regions of two light chain genes in this phylogenetically distant vertebrate have been determined and are reported here. Comparisons of the sequences are consistent with the presence of mammalian-like framework and complementarity-determining regions. The predicted amino acid sequences of the genes are more related to mammalian lambda than to kappa light chains. The nucleotide sequences of the genes are most related to mammalian T-cell antigen receptor beta chain. Heterodontus light chain genes may reflect characteristics of the common ancestor of immunoglobulin and T-cell antigen receptors before its evolutionary diversification.

Amino Acid Sequence↗
PubMed1988

Complete structure and organization of immunoglobulin heavy chain constant region genes in a phylogenetically primitive vertebrate.

Immunoglobulin (Ig) gene organization in Heterodontus francisci (horned shark), a phylogenetically primitive vertebrate, is unique. Homologous Ig heavy chain variable (VH) and constant region (CH) specific probes were used to screen a spleen cDNA library constructed in lambda gt11. Both secretory (SEC) and transmembrane (TM) cDNA clones were recovered; the latter were identified by a negative selection strategy. The complete sequence of the CH portion of a Heterodontus genomic DNA-lambda clone also was determined. The sequences of the individual CH genes differ from each other in all exons. When compared to mammalian prototypes, similarities in exon and intron organization as well as conservation of sequences involved with differential splicing of SEC and TM mRNA indicate that Heterodontus heavy chain genes are of the mu type, although intron lengths are uniformly longer in Heterodontus. Heterodontus genes are not associated, however, with the family of DNA sequences that have been implicated in heavy chain class switching in mammals. Spleen cDNA library screening and RNA blot analyses indicate that mRNAs encoding TM Ig are exceedingly rare. The relationship between this quantitative difference and the distribution of polyadenylation signal sequences suggests that regulation of Ig gene expression in Heterodontus may be highly dependent on position effects.

Amino Acid Sequence↗
PubMed1988

Diverse organization of immunoglobulin VH gene loci in a primitive vertebrate.

The immunoglobulin (Ig) heavy chain variable (VH) gene family of Heterodontus francisci (horned shark), a phylogenetically distant vertebrate, is unique in that VH, diversity (DH), joining (JH) and constant region (CH) gene segments are linked closely, in multiple individual clusters. The V regions of 12 genomic (liver and gonad) DNA clones have been sequenced completely and three organization patterns are evident: (i) VH-D1-D2-JH-CH with unique 12/22 and 12/12 spacers in the respective D recombination signal sequences (RSSs); VH and JH segments have 23 nucleotide (nt) spacers, (ii) VHDH-JH-CH, an unusual germline configuration with joined VH and DH segments and (iii) VHDHJH-CH, with all segmental elements being joined. The latter two configurations do not appear to be pseudogenes. Another VH-D1-D2-JH-CH gene possesses a D1 segment that is flanked by RSSs with 12 nt spacers and a D2 segment with 22/12 spacers. Based on the comparison of spleen, VH+ cDNA sequences to a germline consensus, it is evident that both DH segments as well as junctional and N-type diversity account for Ig variability. In this early vertebrate, the Ig genes share unique properties with higher vertebrate T-cell receptor as well as with Ig and may reflect the structure of a common ancestral antigen binding receptor gene.

Amino Acid Sequence↗
PubMed1987

Atypical glycosylation of an IgG monoclonal cryoimmunoglobulin.

The NH2-terminal amino acid sequence of the heavy chain of the IgG monoclonal cryoimmunoglobulin Ger was determined. Evidence for the glycosylation of the first heavy chain hypervariable region of this protein was found. The inability of the deglycosylated Fab fragment of Ger to inhibit cryoprecipitation provides direct evidence that the presence of an additional sialic acid residue in a heavy chain's first hypervariable region can account for the cryo properties of this protein. This is the first convincing description of a molecular defect that explains the atypical low temperature solubility of a monoclonal cryoimmunoglobulin.

Amino Acid Sequence↗
PubMed1987

Extensive families of constant region genes in a phylogenetically primitive vertebrate indicate an additional level of immunoglobulin complexity.

A homologous probe for the constant region of the Heterodontus francisci (horned shark) immunoglobulin heavy chain was used to screen a genomic DNA library constructed in bacteriophage lambda, and a large number of independent clones were recovered. Their hybridization patterns with segment-specific probes are consistent with the close linkage of heavy-chain constant (CH), joining (JH), and variable (VH) gene segments. Differences in the nucleotide sequences of the first CH exon of five genes primarily are localized to 5' positions; extended regions of sequence identity are noted at 3' positions. The predicted amino acid sequences of each gene are different and are related distantly to the corresponding regions of higher vertebrate immunoglobulins. Gene-specific oligodeoxynucleotide probes were used to establish that at least three of the five genes are transcriptionally active. Quantitative gene titration data are consistent with the large numbers of genes suggested by the library screening analyses. In this representative early vertebrate, it appears that (VH-diversity-JH) segments are associated with individual constant region genes that can differ at the predicted protein level.

Amino Acid Sequence↗
PubMed1986

Putative immunoglobulin VH genes of the goldfish, Carassius auratus, detected by heterologous cross-hybridization with a murine VH probe.

By using a defined cDNA probe for the VH region of a murine phosphocholine-binding myeloma protein (S107) we have defined a family of distinct cross-hybridizing DNA sequences in genomic DNA of the goldfish. The estimated number of the goldfish putative VH family detectable by the S107 probe is about 36. By using two putative goldfish VH probes to analyze, by hybridization, the relationships among seven of the goldfish genomic clones, we have determined that the putative goldfish VH genes recognized by the S107 probe comprise at least several distinct families that are not closely related.

Animals↗
PubMed1986

The effect of interchain disulfide bond cleavage on the cold induced precipitation of cryoimmunoglobulins.

Selective cleavage of the interchain disulfide bonds present in the two IgG1-kappa monoclonal cryoglobulins Ger and Muk results in a partial loss of cryoprecipitability of the parent proteins at 0 degree C. The progressive loss of cryoprecipitability which occurs as a function of increasing reductant concentration parallels the successive cleavage of interheavy-light and interheavy-heavy chain disulfides. Circular dichroism shows that reduction and alkylation of hinge region disulfides induces small conformational changes in the IgG molecules that could alter cryoprecipitability. The N-terminal amino acid sequence of the Fc component derived by restricted proteolysis with trypsin of protein Muk was found to be completely homologous with N-terminal Fc sequences of noncryoglobulin IgG reference proteins, indicating identical hinge regions. Reduction and alkylation of two monoclonal IgM cryoglobulins also reduces cryoprecipitability. After reduction and alkylation of either the monoclonal IgM rheumatoid factor or the polyclonal IgG component of two mixed cryoglobulins recombination results in decreased cryoprecipitation of the intact cryoglobulin complex. In all cases inhibition of cryoprecipitation is greater when iodoacetic acid rather than iodoacetamide is employed as the S-alkylating group. These results do not support a direct role for the hinge region in the precipitation of cryoimmunoglobulins.

Alkylation↗