A novel chimeric Ig heavy chain from a teleost fish shares similarities to IgD.
IgD is considered to be a recently evolved Ig, being previously found only in primates and rodents. Here we describe, from a teleost fish (the channel catfish, Ictalurus punctatus), a novel complex chimeric Ig heavy chain, homologous, in part, to the heavy chain (delta) of IgD. In addition to alternative secretory or membrane-associated C termini, this chimeric molecule contains a rearranged variable domain, the first constant domain of mu, and seven constant domains encoded by a delta gene homolog. Identification of the catfish gene as delta is based on the following properties: sequence relatedness to mammalian delta; a location within the IgH locus that is immediately downstream of the mu gene; separate terminal exons for the secretory and membrane forms; coexpression with the complete mu chain in some but not all B cells. These results (i) suggest that IgD is an ancient immunoglobulin that was present in vertebrates ancestral to both the mammals and the ray-finned fishes, and (ii) raise the possibility that this Ig isotype may have served an as yet unidentified important function early in the evolution of the immune system.
Wilson
M
M
Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216, USA.
Bengtén
E
E
Miller
N W
NW
Clem
L W
LW
Du Pasquier
L
L
Warr
G W
GW
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D018076:DNA, Complementary / Q000235:genetics; D015723:Gene Library; D005803:Genes, Immunoglobulin; D007059:Ictaluridae / Q000235:genetics / Q000276:immunology*; D007072:Immunoglobulin D / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates / Q000235:genetics / Q000276:immunology
D018076:DNA, Complementary; D007072:Immunoglobulin D; D007143:Immunoglobulin Heavy Chains; D011993:Recombinant Fusion Proteins