Axolotl MHC class II β chain: predominance of one allele and alternative splicing of the β1 domain

Abstract

The axolotl MHC is composed of multiple polymorphic class I loci linked to class II B loci. In this report, evidence of the existence of one class II B locus (Amme‐DAB) that codes for two different transcripts is given. A 2.1‐kb transcript is translated to a complete β chain and a shorter transcript of 1.8 kb encodes a molecule lacking the β1 domain. For two complete class II B mRNA synthesized, up to one mRNA devoid of the β1 domain is synthesized. Alternative splicing involving a peptide binding domain at a class II B locus evidenced in axolotl (Ambystoma mexicanum) is also observed for A. trigrinum, the tiger salamander. Very little variability is found among various axolotl MHC class II B cDNA sequences, and the same allele is obtained from inbred and wild axolotls. The transcription of one MHC class B locus in two class II B isoforms in thymic cells and in splenic lymphocytes may shed new light on the well‐known deficient immune responder state of the axolotl.