Characterisation of grass carp (Ctenopharyngodon idellus) MHC class I domain lineages.

In order to characterise grass carp MHC class I (Ctid-MHC I) sequences, 26 Ctid-MHC I genes were cloned from 12 individuals and their alpha domain lineages were analysed. Simultaneously, a quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) assay was developed to detect Ctid-MHC I tissue-specific expression. The results suggested that Ctid-MHC I could be divided into eight lineages (Ctid-NA-Ctid-NH). Based on whether they contained the motif of eight key amino acids (YYRTKWYY), Ctid-MHC I lineages were divided into two groups [Ctid-MHC I (8(+)) and Ctid-MHC I (8(-))]. The expression analysis showed that the Ctid-MHC I locus/loci appeared in the kidney, gill, intestine, heart, spleen, liver, and brain. A GenBank homology BLAST was performed independently with each alpha domain, and Ctid-MHC I alpha1, alpha2, and alpha3 were categorised into two (V and IX), five (II, IV-VII), and four (IV-VII) domain lineages, respectively. Based on the alphabetic labelling system created in our earlier studies, one alpha1 (IX), four alpha2 (IV-VII), and unique alpha3 (V-VII) domain lineages were observed in grass carp and across the teleostean species.