Cloning and structure of a histocompatibility class IIA gene (Lelo-DAA) in Chinese longsnout catfish (Leiocassis longirostris)

Here, the major histocompatibility complex (MHC) class II alpha chain gene in the Chinese longsnout catfish (Leiocassis longirostris) was characterized through cloning, sequencing, polymorphism analysis, and expression patterns in various tissues. The full-length LeloDAA cDNA comprises 1,114 bp with a 5'-UTR region of 79 bp, an open reading frame of 714 bp and a 3'-UTR of 302 bp. The deduced protein sequence shows the following important features: leader peptide, alpha 1, alpha 2, and CP/TM/CYT regions. Using long PCR techniques, the genomic sequence was further identified to be 2,093 bp in length, containing four exons and three introns. Three class IIA alleles were identified from four individuals. Two different alleles observed (at most) in each individual suggest the existence of a single locus of class IIA gene in the Chinese longsnout catfish genome. This locus is polymorphic and most of the amino acidic changes occurred in the alpha 1 domain containing the peptide-binding region. Lelo-DAA mRNA expression was mainly found in the intestine, gills, spleen, head kidney and liver; minor expression was detected in the stomach, skin, heart and muscle. Our results yield insight into Chinese longsnout catfish T cell immune responses and will aid future work on the genetic status of this economically important species.