Structural changes in the proximal tubule of the short-toes axolotl mutant

A recessive lethal mutation in axolotls that involves the kidneys, the Mullerian ducts and the limbs was described by Humphrey (1967). In the present experiments, we have examined the structural defects that lead to kidney malfunction and subsequent death in homozygous mutants and compared the defects with those observed in other axolotls lacking this mutant gene. The ultrastructure of the mesonephric kidney was studied in homozygous s/s short-toes axolotls with ascites and/or edema and hemorrhages (group 1a); in s/s short-toes axolotls not yet expressing kidney malfunction symptoms (group 1b); in normal siblings, either +/+ or +/s, without affected limbs but possibly heterozygous for the 's' gene (group 1c); in +/+ animals with malfunctioning kidneys that lack the short-toes gene (group 2a) and in normal +/+ animals from different gene pools (group 2b). In all of the short-toes animals that expressed pathological phenotypes, the proximal tubule showed abnormal morphology. There was no morphological evidence of kidney abnormality in the siblings having normal limbs or in the group 1b axolotls examined. However, mesonephroi from animals (group 2a) of other gene pools that had ascites exhibited a different and more pronounced pathology. On the basis of the dramatically distinct proximal tubule pathology of the sporadic floaters, we conclude that this phenotype is more likely caused by infection than to a variant of the short-toes gene.