Abstract
BACKGROUND: We previously reported the genomic characterization of immunoglobulin loci in Ambystoma mexicanum of the laboratory d/d white strain, where the IGH locus gene orientation was incompatible with VDJ recombination, suggesting scaffold orientation errors. A novel 29.1 Gbp A. mexicanum genome derived from an F1 cross between A. mexicanum and A. tigrinum (UKY_AmexF1_1) has recently been released, containing only 220 unmapped scaffolds. Here, we present an updated description of the immunoglobulin loci based on this improved genome assembly. METHODS: Using our previously annotated AmbMex60DD sequences, we performed an alignment-based annotation followed by manual curation on the UKY_AmexF1_1 assembly. Gene models were further refined using RNA-Seq datasets from axolotl spleen, liver, lung, heart, and gill tissues. RESULTS: The IGH locus was mapped at 350-364 Mbp on chromosome 13q. Synteny is preserved between both genome versions, but in UKY_AmexF1_1, all IGH genes share the same transcriptional orientation. A major difference was observed in the lambda locus, which in the UKY_Amex_F1_1 genome contains 13 IGLC-IGLJ clusters comprising 60 IGLJ genes, compared with only three clusters in the AmbMex60DD genome. No kappa locus was detected in either assembly. CONCLUSION: This study confirms our previous findings and provides an example of intraspecies structural variation in adaptive immune receptor loci. It underscores the importance of well-assembled genomes and establishes the current A. mexicanum reference as a valuable resource for investigating immune evolution and function in axolotls and other vertebrates.