Identification of Mutant Genes and Introgressed Tiger Salamander DNA in the Laboratory Axolotl, Ambystoma mexicanum

M Ryan Woodcock,D Kevin Kump,Jennifer Vaughn-Wolfe,Nataliya Timoshevskaya,Jessica E Spiewak,Dustin W Perry,S Randal Voss,Alexandra Elias,Jeramiah J Smith,Vladimir Timoshevskiy,David M Parichy,Katharina Denise Kendall

doi:10.1038/s41598-017-00059-1

Abstract

The molecular genetic toolkit of the Mexican axolotl, a classic model organism, has matured to the point where it is now possible to identify genes for mutant phenotypes. We used a positional cloning–candidate gene approach to identify molecular bases for two historic axolotl pigment phenotypes: white and albino. White (d/d) mutants have defects in pigment cell morphogenesis and differentiation, whereas albino (a/a) mutants lack melanin. We identified in white mutants a transcriptional defect in endothelin 3 (edn3), encoding a peptide factor that promotes pigment cell migration and differentiation in other vertebrates. Transgenic restoration of Edn3 expression rescued the homozygous white mutant phenotype. We mapped the albino locus to tyrosinase (tyr) and identified polymorphisms shared between the albino allele (tyra) and tyr alleles in a Minnesota population of tiger salamanders from which the albino trait was introgressed. tyra has a 142 bp deletion and similar engineered alleles recapitulated the albino phenotype. Finally, we show that historical introgression of tyra significantly altered genomic composition of the laboratory axolotl, yielding a distinct, hybrid strain of ambystomatid salamander. Our results demonstrate the feasibility of identifying genes for traits in the laboratory Mexican axolotl.

Highlights

The molecular genetic toolkit of the Mexican axolotl, a classic model organism, has matured to the point where it is possible to identify genes for mutant phenotypes
We identified in white mutants a transcriptional defect in endothelin 3, encoding a peptide factor that promotes pigment cell migration and differentiation in other vertebrates
In 1962, a terrestrial tiger salamander (A. tigrinum) lacking melanin was collected near Foot Lake, Willmar Minnesota and after almost a year in captivity, it was gifted to Rufus Humphrey at Indiana University

Summary

Introduction

The molecular genetic toolkit of the Mexican axolotl, a classic model organism, has matured to the point where it is possible to identify genes for mutant phenotypes. Genomic resources have been developed to enable comparative genomics, quantitative trait locus mapping, gene expression analysis, and the creation of transgenic lines and targeted knock-outs[2,3,4,5,6,7,8,9] These efforts have brought the axolotl closer to becoming a genetic model organism, that is, a model that can be used to identify genes for phenotypes that are best studied using the axolotl. Humphrey and colleagues used cutting edge technologies for the time – somatic cell nuclear transfer and microsurgery – to create embryos that carried the albino gene Descendants of these species hybrids were crossed into various axolotl strains and are maintained today in the Ambystoma Genetic Stock Center (AGSC; University of Kentucky)

Methods

Results

Conclusion