Suggestive association of major histocompatibility IB genetic markers with resistance to bacterial cold water disease in rainbow trout (Oncorhynchus mykiss)

Authors: JOHNSON, NATHAN - VIRGINIA TECH; Vallejo, Roger; SILVERSTEIN, JEFFREY - GEORGE WASH CARVER CENTER; Welch, Timothy - Tim; Wiens, Gregory - Greg; HALLERMAN, ERIC - VIRGINIA POLYTECH INST. &; Palti, Yniv

Submitted to: Marine Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2008
Publication Date: 6/1/2008
Citation: Johnson, N., Vallejo, R.L., Silverstein, J., Welch, T.J., Wiens, G.D., Hallerman, E.M., Palti, Y. 2008. Suggestive association of major histocompatibility IB genetic markers with resistance to bacterial cold water disease in rainbow trout (Oncorhynchus mykiss). Marine Biotechnology. 10:429-437.

Interpretive Summary: The gram-negative bacterium, Flavobacterium psychrophilum (Fp), poses a major fish health concern for trout and salmon aquaculture around the world, and has been documented to cause mortalities as high as 90% in some epizootics. Losses are especially severe in young fish, which may limit the use of vaccination as a control method. Methods for control of the disease are needed and selective breeding for disease resistant lines is a promising solution in the absence of approved, cost-effective vaccination methods. The identification of genes involved in resistance or susceptibility to the disease and subsequent examination on how those genes affect the resistance mechanism(s) will enhance genetic improvement. Molecules encoded by major histocompatibility (MH) genes are cell-surface integral membrane glycoproteins responsible for detection, regulation and elimination of pathogenic cells. They bind antigens and present them to the adaptive and cellular immune systems, which are essential components of the response against invading pathogens. Here, we examine the involvement of four MH genomic regions in rainbow trout in resistance to the disease. Eight DNA markers were previously isolated from MH gene-containing regions and mapped onto the rainbow trout genetic linkage map. MH-IB and MH-II markers were linked to resistance when data were analyzed by family. Tests for disease association at the population level substantiated the involvement of MH-IB, but not MH-II, with disease resistance.

Technical Abstract: Genes within the major histocompatability complex (MHC) are important for both innate and adaptive immune responses in mammals, but much less is known regarding their contribution in teleost fishes. Here, we examine the involvement of four major histocompatibility (MH) genomic regions in rainbow trout in resistance to the causative agent of bacterial coldwater disease (BCWD), Flavobacterium psychrophilum. Fish from the 2005 NCCCWA brood-year (71 full-sib families) were challenged with F. psychrophilum strain CSF 259-93. The overall mortality rate was 70%, with large variation in mortality between families. Disease resistance was quantified as post-challenge days to death. Phenotypic variation and additive genetic variation were estimated using mixed models of survival analysis. To examine association, eight microsatellite markers were isolated from MH gene-containing BAC clones and mapped onto the rainbow trout genetic linkage map. The parents and grandparents of the 2005 brood-year families were genotyped with these eight markers and another two markers tightly linked to the MH-IB region to assess the extent of linkage disequilibrium (LD) of MH genomic regions MH-IA, MH-IB, TAP1 and MH-II with survival post-challenge. MH-IB and MH-II markers were linked to BCWD survivability when data were analyzed by family. Tests for disease association at the population level substantiated the involvement of MH-IB, but not MH-II, with disease resistance. The impact of selective breeding for disease resistance on MH sequence variation is discussed in the context of aquaculture production.