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Updated: Aug 15, 2026
Raising the Mexican Tetra Astyanax mexicanus for Analysis of Post-larval Phenotypes and Whole-mount Immunohistochemistry
Published on: December 28, 2018
Genetic and experimental studies on three associated mutant genes in the Mexican axolotl: st (for stasis), mi (for
Abstract:
Three mutant genes, st, mi, and h, were discovered in an axolotl male received from Mexico City. All three are recessive to their normal alleles, and appear to segregate independently. Larvae homozygous for st (for stasis) suffer blockage of the circulation at hatching or shortly after, and the majority soon die; any surviving live only a few weeks at most. The mi/mi (microphthalmic) can be identified at the feeding stage. None survives more than a few days. The h/h (hand lethals) live until the digits have appeared on the forelimb. They may then be recognized by the thumb-like orientation of digit 1. Transplants from st/st embryos into normal produce normal structures which persist indefinitely. Those from mi/mi and h/h donors do not survive. The structures (forelimb, gills) derived from h/h donors grow for a relatively long time, and their final death and degeneration result in defects leading to death of most of the recipients. Parabiosis is of no benefit to st/st or h/h mutants and leads to the death of the normal twin; mi/mi mutants undergo a gradual absorption by the normal twin.
Insights
Three new recessive axolotl genes (stasis, microphthalmia, and hand lethals) were identified. These mutations cause severe developmental defects, impacting circulation, eye development, and limb formation, leading to early mortality in homozygous mutants.
Area of Science:
- Developmental genetics
- Axolotl biology
- Mutant gene analysis
Background:
- Three novel recessive mutations (st, mi, h) were identified in an axolotl from Mexico City.
- These mutations affect critical developmental processes, including circulation, eye formation, and limb development.
Purpose of the Study:
- To characterize the phenotypic effects of three newly discovered recessive axolotl mutations.
- To investigate the developmental impact and viability of homozygous mutants for stasis (st), microphthalmia (mi), and hand lethals (h).
Main Methods:
- Genetic analysis of three recessive mutations in axolotls.
- Phenotypic characterization of homozygous mutants (st/st, mi/mi, h/h).
- Embryo transplantation experiments and parabiosis assays.
Main Results:
- Homozygous st/st mutants exhibit circulatory failure and early death.
- Homozygous mi/mi mutants display microphthalmia and die within days.
- Homozygous h/h mutants develop limb abnormalities, specifically digit 1 orientation, and die after digit formation.
- Transplants from st/st embryos into normal hosts develop normally; transplants from mi/mi and h/h do not survive.
- Parabiosis offers no benefit to st/st or h/h mutants, causing normal twin death, while mi/mi mutants are absorbed by normal twins.
Conclusions:
- The identified mutations (st, mi, h) represent critical developmental lethals in axolotls.
- These genes play essential roles in embryonic and larval development, affecting circulation, eye, and limb formation.
- Transplantation and parabiosis studies reveal distinct cellular and developmental interactions of these mutants.
