Experimental studies on a lethal gene (t) in the Mexican axolotl, Ambystoma mexicanum

In the Mexican axolotl, Ambystoma mexicanum, the developmental mutation lethal t is inherited as a simple Mendelian recessive. Mutant larvae failed to feed and died, on the average, 17 days after hatching. Unfed wild-type larvae died an average of 23 days after hatching. By 15 days, forelimb development had progressed further in the wild type; a cartilaginous scapula and humerus were present, but no cartilage was seen in the mutant limb. Histological examination indicated that the visceral cartilage may also be abnormal, and the rectus cervicus muscle was found to have fewer and smaller fibers. Though the mutant was not rescued by parabiosis with wild-type embryos, transplants of presumptive gill and limb tissue to wild-type hosts survived, indicating that the mutation is not an autonomous cell lethal.