Cloning and characterization of major histocompatibility complex class II genes in the stone flounder Kareius bicoloratus (Pleuronectidae)

Abstract

ABSTRACT. Major histocompatibility complex (MHC) class II genes play important recognition roles in the immune system in vertebrates. We cloned the MHC class II genes A and B in the stone flounder (Kareius bicoloratus). The full-length cDNA and DNA sequences of both genes were obtained, and their characteristic motifs were analyzed. The DNA sequence of stone flounder MHC class II A consists of four exons, while gene B contains six exons. The extra intron in gene B might be a common feature in most of its Acanthopterygii orthologs. Several conserved motifs were identified by multiple deduced amino acid sequence alignments of the two genes and their orthologs. The peptide sequences of α chain and β chain shared identity of 86.0-30.1% and 69.8-31.3% with their orthologs, respectively. Bayes phylogenetic trees showed that the stone flounder is closely related to the spotted halibut (Verasper variegates), and the half-smooth tongue sole (Cynoglossus semilaevis). Real-time quantitative PCR showed that in the stone flounder, both genes A and B are highly or moderately MHC class II genes cloning in stone flounder expressed in several tissues, including the intestine, spleen and gills, and less expressed or undetectable in the liver, kidney, brain, heart, and gonads. These expression patterns differed slightly from those in other teleosts. This might be a unique phenomenon in the stone flounder. This first study of MHC genes in stone flounder could provide reference data for comparative studies.

Duplicated major histocompatibility complex class II genes in the tongue sole (Cynoglossus semilaevis)

“…Compared to the cDNA sequence (Li et al., ), tongue sole class II A genes’ exon 1 encodes the signal peptide, exon 2 encodes the α1 domain, exon 3 encodes the α2 domain, and exon 4 encodes the connecting peptide, transmembrane region and cytoplasmic domain. Tongue sole's two class II A genes have the same exon 2–4 length distribution as Japanese flounder (Xu & Chen, ), stone flounder (Jiang et al., ) and Miiuy croaker ( Miichthys miluy ) (Xu, Sun, Shi, Cheng, & Wang, ), indicating gene conservation and a close relationship among these species. On the other hand, their intron lengths are distinct, which suggests gene evolution in different species.…”

“…Interestingly, both class II A and class II B genes are highly polymorphic in teleosts (Gomez, Conejeros, Marshall, & Consuegra, ; Kruiswijk et al., ; Li, Jiang, et al., ; Pang et al., ), which is in contrast to mammals and birds where most or all of the variation is found in the class II B gene (Hughes, Miles, & Walbroehl, ; Reche & Reinherz, ). In Pleuronectiformes, MHC class II genes contain similar characteristics as other teleosts (Jiang, Li, Zhang, & Wang, ; Li, Jiang, et al., ; Zhang & Chen, ; Zhang, Chen, Liu, Sha, & Liu, ), and most studies focus on characterizing gene polymorphism and expression patterns (Zhang & Chen, ; Zhang et al., ). However, there are very few studies of teleosts where allelic variation is linked to specific loci.…”

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“…For example, in large yellow croaker, MHC class II α mRNA was highly expressed in kidney, intestine, gills, and spleen (Yu, Ao, & Chen, 2010). Similarly, in stone flounder and blunt snout bream, MHC class II α mRNA expression was highest in the gills, followed by intestines and spleen (Jiang, Li, Zhang, & Wang, 2013;Luo et al, 2014). Finally, in gilthead seabream, MHC class II α mRNA was expressed in head-kidney leucocyte subpopulations, including acidophilic granulocytes, lymphocytes, and MO/MФ (Cuesta, Esteban, & Meseguer,2006).…”

“…Moreover, the TM region of PaMHCIIα contained the GxxxGxxGxxxG motif, shared across fishes and mammals (Cosson & Bonifacino, 1992;Xu, Sun, Shi, Cheng, & Wang, 2011;Jiang, Li, Zhang, & Wang, 2013;Luo et al, 2014;Wang, Tan, & Cai, 2015). PaMHCIIα has only one N-linked glycosylation site, consistent with most teleosts (Nath, Kales, Fujiki, & Dixon,2006;Cuesta, Esteban, & Meseguer, 2006;Yu, Ao, & Chen, 2010;Jiang, Li, Zhang, & Wang, 2013;Luo et al, 2014) except zebrafish (Sültmann, Mayer, Figueroa, O'hUigin, & Klein, 1993), channel catfish (Thankappan, Fuller, Godwin, Kearse, & McConnell, 2006), andstickleback (Gasterosteus aculeatus) (Scharsack, Kalbe, & Schaschl,2007). In contrast, human and mouse MHC class II α proteins have two N-linked glycosylation sites (Nag et al, 1994; anguillarum.…”

“…The deduced peptide contained typical structural features of the class-including the SP, CP/TM/CYT, and extracellular (α1/α2) domainsconsistent with other species (Cuesta, Esteban, & Meseguer, 2006;Xu, Sun, Shi, Cheng, & Wang, 2011;Luo et al, 2014;Wang, Tan, & Cai, 2015). Moreover, the TM region of PaMHCIIα contained the GxxxGxxGxxxG motif, shared across fishes and mammals (Cosson & Bonifacino, 1992;Xu, Sun, Shi, Cheng, & Wang, 2011;Jiang, Li, Zhang, & Wang, 2013;Luo et al, 2014;Wang, Tan, & Cai, 2015). PaMHCIIα has only one N-linked glycosylation site, consistent with most teleosts (Nath, Kales, Fujiki, & Dixon,2006;Cuesta, Esteban, & Meseguer, 2006;Yu, Ao, & Chen, 2010;Jiang, Li, Zhang, & Wang, 2013;Luo et al, 2014) except zebrafish (Sültmann, Mayer, Figueroa, O'hUigin, & Klein, 1993), channel catfish (Thankappan, Fuller, Godwin, Kearse, & McConnell, 2006), andstickleback (Gasterosteus aculeatus) (Scharsack, Kalbe, & Schaschl,2007).…”