2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to identify DNA clones containing the catfish immunoglobin heavy chain locus, sequence these clones, and establish the gene structure in this locus. 1b.Approach (from AD-416) Clones from a bacterial artificial library containing 150-200,000 base pair inserts will be identified by PCR-amplification screening. The BAC clones will be fragmented and subcloned into a plasmid vector. The plasmid subclones will be arrayed in 96-well format and sequenced using high-throughput technology. Sequences will be assembled using computer algorithms. Sequence information from individual clones will be used to design PCR primers to identify subsequent clones containing flanking genomic DNA, and the process will be continued until the entire locus (approximately 700,000 base pairs) is sequenced. 3.Progress Report This report serves to document research conducted under a Reimbursable Agreement between ARS and the University of Mississippi Medical Center. Additional details of research can be found in the report for the in-house project 6402-31000-008-00D, “Catfish Genetics, Breeding, and Physiology.” The ADODR and another Catfish Genetics Research (CGRU) SY remain in regular contact with the cooperators through site visits, email, and telephone communication to assess project progress. The channel catfish immune system has been the best characterized for any teleost and this research continued the work toward characterization of the immunoglobin heavy chain locus. Large scale DNA cloning and sequencing has provided details on the structure of this genetic locus that encodes part of the antibody molecule and has shown the immunoglobin heavy chain locus has undergone multiple internal duplications and transpositions. The immunoglobin locus contains 55 VH, 6 D, 12 JH genes and the IGH constant region genes encoding the functional secreted and membrane forms of IgM and the membrane form of IgD. Rearrangement of genes in immune cells provides new combinations that increase the antibody diversity in catfish. The channel catfish IGH sequencing project will complement any other future somatic mutation studies by delineating the precise mechanisms that generate catfish antibody binding diversity. At the present, this analysis represents an important step in defining the channel catfish IGH total germline coding potential. It also demonstrated that IGH loci in bony fish can vary from species to species, particularly in the numbers of genes, the location, and duplication of specific regions of the gene. Better understanding of the catfish immune system will help breeders identify broodfish with increased potential for resistance to pathogens common to production settings.