A Review of the Eyeless Mutant in the Mexican Axolotl

SYNOPSIS. As a homozygous recessive, gene e in the Mexican axolotlprevents optic vesicles from forming, thus producing an eyelessanimal. Previous experimental evidence has indicated that thegene acts by affecting the ability of anterior medullary plateectoderm in the eye field to respond to inductive mesodermalsignals. Other possible mechanisms of gene action are described.The hypothalamus is also affected and "eyeless" animals aresterile. The absence of eyes results in increased levels ofcirculating MSH and thus the animal is also highly pigmented.Eyes may be grafted into the heads of "eyeless" axolotls. Theseeyes become functional and lead to normal pigmentation. Whenpresent as a homozygous recessive, gene r acts to allow thepenetration of heterozygous e (E/e r/r). This results in abnormaleye development.