Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

Genomic Analysis Of The Rainbow Trout IgH Regions: Unexpected Discovery Of A Third Expressed Isotype

John D Hansen^{1, 2} , Eric Landis³ , Jenefer DeKoning⁴ , Ruth Phillips⁴

¹  Department of Pathobiology, University of Washington, Seattle, WA, 98195, USA.

²  U.S. Geological Survey, Western Fisheries Research Center, Seattle, WA, 98115, USA.

³  Molecular and Cellular Biology Program, University of Maryland, Baltimore, MD, 21202.

⁴  School of Biological Sciences, Washington State University, Vancouver, WA, 98686, USA.

Jawed vertebrates are the only animal taxa to possess an adaptive immune response based on the somatic recombination of antigen receptors (Ig/TCR). IgM is the only antibody class that is found throughout all vertebrates, and up until 1997, it was believed that teleost fish only possessed IgM until the discovery of the IgD isotype in channel catfish. Recent analysis of the rainbow trout EST database resulted in the discovery of a unique sequence that possessed two IgSf C1 domains, similar to that of monomeric forms of Ig. Full-length cDNAs were then isolated from an OSU-142 (homozygous) splenic library resulting in the sequence characterization of a novel Ig isotype possessing a signal peptide, a rearranged variable domain (including D and J elements) followed by four IgSf C1 domains ending in either a transmembrane or secretory region. Concurrently, we isolated IgD from trout to confirm that the newly discovered isotype was not a unique variant of trout IgD. All three trout Ig isotypes are expressed primarily within lymphoid tissues and all utilize the same variable (Vh) region gene families. We have physically and genetically mapped the trout IgH genes and will discuss our recent sequence analysis of BAC clones harboring all three isotypes. Finally, bioinformatic analysis revealed no true orthalogous sequences outside of teleost fish, implying that this Ig isotype is likely restricted to bony fish. Based upon our analysis, we have dubbed this novel isotype as Igt (tau), for teleost fish.