Characterization of cDNA encoding immunoglobulin light chain of the mandarin fish ( Siniperca chuatsi)

Abstract

Immunoglobulin light chain cDNA sequences of a perciform fish, the mandarin fish Siniperca chuatsi were amplified from head kidney mRNA by reverse transcription (RT)-PCR and RACE methods using degenerated primer and gene specific ones. In cDNA sequences of the VL region, nucleotide exchanges were present mainly within CDRs, although a lesser degree of variability was also found in FRs. Moreover, the length of CDR1 and CDR3 in the mandarin fish is shorter than in most other fish species. In the middle of S. chuatsi CL region, a microsatellite sequence (AGC) 6–8 was found, which is also present in another perciform species, the spotted wolffish ( Anarhichas minor). The comparison of amino acid sequence of the mandarin fish CL domain with those of other vertebrates showed the highest degree of similarity of 94.5% to the spotted wolffish, while the similarity with rainbow trout ( Oncorhynchus mykiss) Ig L1 (62.7%) and channel catfish ( Ictalurus punctatus) Ig LG (55.9%) isotypes is also higher. However, there is only 50% identity in the VL regions between the mandarin fish and the wolffish. The sequence similarity of the mandarin fish CL domain with those of higher vertebrate did not readily allow it to be classified as κ or λ isotype. The phylogenetic analyses also demonstrated that the CL genes of the mandarin fish and most other teleost fish cluster as a separate branch out of the mammal κ and λ branches.