title: Two distinct immunoglobulin heavy chain isotypes in a primitive, cartilaginous fish, Raja erinacea.
abstract: 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.
authors.affiliation: Tampa Bay Research Institute, St Petersburg, FL 33716.
authors.forename: F A
authors.initials: FA
authors.lastname: Harding
authors.forename: C T
authors.initials: CT
authors.lastname: Amemiya
authors.forename: R T
authors.initials: RT
authors.lastname: Litman
authors.forename: N
authors.initials: N
authors.lastname: Cohen
authors.forename: G W
authors.initials: GW
authors.lastname: Litman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D005091:Exons; D015723:Gene Library; D005803:Genes, Immunoglobulin; D015698:Genomic Library; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007132:Immunoglobulin Isotypes / Q000235:genetics*; D007148:Immunoglobulin mu-Chains / Q000235:genetics; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D012860:Skates, Fish / Q000235:genetics / Q000276:immunology*; D013154:Spleen / Q000276:immunology
chemical_list: D007127:Immunoglobulin Constant Regions; D007143:Immunoglobulin Heavy Chains; D007132:Immunoglobulin Isotypes; D007148:Immunoglobulin mu-Chains