Plant & Animal Genomes XI Conference

January 11-15, 2003
Town & Country Convention Center
San Diego, CA

Workshop: Aquaculture
            

FUNCTIONAL AND MOLECULAR CHARACTERIZATION OF THE REARRANGING IG AND TCR LOCI UN CHANNEL CATFISH, ,ICTALURUS PUNCTATUS

¹ Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216, USA

² Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, 29425, USA

³ Department of Medicine, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS, 39216, USA

In vivo and in vitro functional studies have demonstrated that teleosts exhibit a wide variety of innate and adaptive immune responses essentially similar to those found in mammals. The identification of numerous relevant genes has confirmed that basic aspects of immunity are highly conserved. Examples of such genes include those for immunoglobulin (Ig) and T cell receptor (TCR). However, in teleosts, both Ig and TCR genes have novel features, suggesting that certain aspects of teleost immune responses are somewhat different from those of mammals. For example, the second Ig isotype in fish, first identified in catfish, is homologous, in part, to mammalian IgD, albeit appearing to be chimeric, consisting of a rearranged VDJ, a C µ 1 exon and seven novel C-regions. Mapping and genomic analyses revealed the presence of three delta genes in catfish, each linked to a µ gene or pseudogene. Moreover, DNA and protein sequencing show that the secreted and membrane forms of fish IgD are encoded by separate genes and not, as in mammals, by differential splicing of a primary mRNA transcript. At present the function(s) of the different catfish IgD forms is unknown. Sequencing of the catfish TCRB locus has also revealed unique features including twenty-nine JB genes and two substantially different CB genes downstream of a single DB gene. This contrasts with the situation in mammals where two clusters of a single DB, 6 or 7 JB genes and a CB gene are found in tandem. The functional significance of the two catfish TCR beta genes is currently unknown.