Major Histocompatibility Complex Class IIB Allele Polymorphism and Its Association with Resistance/Susceptibility to Vibrio anguillarum in Japanese Flounder (Paralichthys olivaceus)

Abstract

The full length of major histocompatibility complex (MHC) class IIB cDNA was cloned from a Chinese population of Paralichthys olivaceus by homology cloning and rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR). The MHC IIB genomic sequence is 1,864 bp long and consists of 34-bp 5'UTR, 741-bp open reading frame, 407-bp 3'UTR, 96-bp intron1, 392-bp intron2, 85-bp intron3, and 109-bp intron4. Phylogenetic analysis showed that the putative MHC class IIB amino acid of the Chinese P. olivaceus shared 28.3% to 85.4% identity with that of the reported MHC class IIB in other species. A significant association between MHC IIB polymorphism and disease resistance/susceptibility was found in Chinese P. olivaceus. Thirteen different MHC IIB alleles were identified among 411 clones from 84 individuals. Among the 280 (268) nucleotides, 32 (11.4%) nucleotide positions were variable. Most alleles such as alleles a, b, c, d, e, f, j, k, i, m were commonly found in both resistant and susceptible stock. Via chi2 test, allele d was significantly more prevalent in individuals from susceptible stock than from resistant stock, and their percentages were 23.80% and 7.14%, respectively. In addition, allele g occurred in 9 and allele h in 4 of 42 resistant individuals that were not present in the susceptible stock; their percentages were 21.4% and 9.52%, respectively. Although allele l was found only in 8 individuals from the susceptible stock, its percentage is 19.05%.

Genetic and genomic analyses for economically important traits and their applications in molecular breeding of cultured fish

“…For example, Palti et al [44] reported that MHCII alleles are significantly associated with anti-IHN in rainbow trout. Zhang et al [45] and Xu et al [46] successfully screened for anti-disease molecular markers by comparing the polymorphisms of Japanese flounder groups susceptible and resistant to Vibrio anguillarum.…”

Diversity of immune genes and associated gill microbes of European plaice Pleuronectes platessa

“…Primers were designed from the sequence of a 3 0 -RACE-PCR product previously obtained by following the SMART-RACE protocol (Clontech, Saint-Germain-enLaye, F) using a conserved flatfish MHC class IIB forward primer (Zhang et al, 2006). This PCR product covered the region from the start of the exon 2 to the 3 0 -end of the transcript.…”

“…Inserts were amplified using M13 primers and sent out for sequencing (Microsynth, Balgen, CH). Sequences were aligned with Japanese Flounder sequences (Zhang et al, 2006) to identify putative exoneexon boundaries, which we then used to design internal exon 2 primers in conserved parts of the gene. PCR reactions contained 1 ml of undiluted DNA extract, 0.05 ml of Hot start taq (5 units ml…”

“…Since higher individual MHC diversity means better immunological surveillance, heterozygote advantage is an obvious mechanism of balancing selection that can maintain genetic diversity (Doherty and Zinkernagel, 1975), and could explain resistance against several disease agents in many vertebrate taxa, for example, salmonids (Arkush et al, 2002;Turner et al, 2007). MHC genes are also polymorphic in flatfish species, and can partly account for resistance against the widespread bacterial fish pathogen Vibrio/Listonella anguillarum in Japanese Flounder Paralichthys olivaceus (Zhang et al, 2006). Such bacterial pathogens may cause high mortalities not only in flat fish (Zheng et al, 2004;Zhang et al, 2006), but also in fish in general (Austin and Austin, 2007).…”

“…MHC genes are also polymorphic in flatfish species, and can partly account for resistance against the widespread bacterial fish pathogen Vibrio/Listonella anguillarum in Japanese Flounder Paralichthys olivaceus (Zhang et al, 2006). Such bacterial pathogens may cause high mortalities not only in flat fish (Zheng et al, 2004;Zhang et al, 2006), but also in fish in general (Austin and Austin, 2007).…”