Analysis of genomic and expressed major histocompatibility class�Ia and class�II genes in a hexaploid Lake Tana African ?large? barb individual (Barbus intermedius)

Abstract

Expression of too many co-dominant major histocompatibility complex (MHC) alleles is thought to be detrimental to proper functioning of the immune system. Polyploidy of the genome will increase the number of expressed MHC genes unless they are prone to a silencing mechanism. In polyploid Xenopus species, the number of MHC class I and II genes has been physically reduced, as it does not increase with higher ploidy genomes. In the zebrafish some class II B loci have been silenced, as only two genomically bona fide loci, DAA/DAB and DEA/DEB, have been described. Earlier studies indicated a reduction in the number of genomic and expressed class II MHC genes in a hexaploid African 'large' barb. This prompted us to study the number of MHC genes present in the genome of an African 'large' barb individual (Barbus intermedius) in relation to those expressed, adopting the following strategy. Full-length cDNA sequences were generated from mRNA and compared with partial genomic class Ia and II sequences generated by PCR using the same primer set. In addition, we performed Southern hybridizations to obtain a verification of the number of class I and II B genes. Our study revealed three beta2-microglobulin, five class Ia, four class II A, and four class II B genes at the genomic level, which were shown to be expressed in the hexaploid barb individual. The class Ia and class II data indicate that the ploidy status does not correlate with the presence and expression of these MHC genes.

Major histocompatibility complex class IIA and IIB genes of the spotted halibut Verasper variegatus: genomic structure, molecular polymorphism, and expression analysis

“…Different class IIA numbers were also found in other fish species, such as two loci have been found both in trout and half-smooth tongue sole Xu et al 2009). More than four alleles of MHC class IIB have also been identified in one single individual in other fish species, which also suggested the existence of at least three loci of class IIB (Kruiswijk et al 2004;Chen et al 2006;Xu et al 2009;. Real-time PCR analysis demonstrated that the spotted halibut MHC IIA and IIB mRNA were expressed in all tested tissues, with high expression in the kidney, spleen, and gill.…”

Identification of two major histocompatibility (MH) class II A genes and their association to Vibrio anguillarum infection in half-smooth tongue sole (Cynoglossus semilaevis)

“…The characteristics of ORF and the deduced proteins of highly polymorphic MH class II A genes from half-smooth tongue sole were all similar to those from other species (van Erp et al, 1996;Hardee et al, 1995;Cuesta et al, 2006;Stet et al, 2002;Kruiswijk et al, 2004;Zhang and Chen, 2007;Yu et al, 2009). The 25 alleles in half-smooth tongue sole could noticeably be clustered to two groups with distinct amino acid sequences, which indicated that the two groups of alleles belonged to two different genes.…”

“…All the 200 individuals in the challenge test consisted of two A genes, and different conserved amino acids in specific positions were observed in their alleles. Similarly, two or more class II A genes in other teleost have been reported, such as the two linked genes (Gaac-DAA and Gaac-DBA) in three-spined stickleback (Reusch et al, 2004), two linked groups DAA and DBA/DCA in Peacock cichlid (Murray et al, 2000), two genes in channel catfish (Godwin et al, 2000;Quiniou et al, 2005), four genes in large barb (Kruiswijk et al, 2004) and Atlantic salmon (Harstad et al, 2008).…”

Patterns of variability at the major histocompatibility class I and class II loci in populations of the endangered cyprinid Ladigesocypris ghigii

“…In 1990, Hashimoto et al reported the first MHC genes in the common carp (Cyprinus carpio). Since then, class I, class IIa and class IIb genes have been identified in a large variety of cyprinid species Kruiswijk et al 2002Kruiswijk et al , 2004Ottová et al 2005;Takeuchi et al 1995;van Erp et al 1996). Data obtained were compared with the patterns of genetic variability revealed previously by RAPD and mitochondrial DNA (mtDNA) genetic markers (Mamuris et al 2005) in order to determine the extent that genetic drift and natural selection may shape genetic variation at MHC loci in this endemic species and to develop conservation rationale.…”