Author

William Jeffery
http://www.life.umd.edu/labs/jeffery

Additional Author(s): Yoshiyuki Yamamoto

Published on SDB CoRe: Feb 15 2013

Ectoderm-derived: Nervous System; Neural Crest
Evolutionary Developmental Biology: Developmental Modifications
Organism: Cavefish
Stage of Development: Adult

Object Description

Astyanax mexicanus is a fish species native to Mexico with both surface dwelling (top left) and cave forms (top right).  The cavefish evolved from surface fish ancestors following isolation in lightless caves.  They feature a loss of both eyes and pigment.  The eye primordium initially forms in the cavefish embryo, but degenerates—including apoptosis and failure of the lens to differentiate.  The lens normally induces other tissues like the cornea and iris to develop.  When it is surgically removed from surface fish embryos (bottom left), the adult eye is reduced in size and sinks into the orbit, mimicking the situation in cavefish. Sonic hedgehog (Shh) signaling is important for proper eye development.  In cavefish, the expression domain of shh along the midline is expanded, inhibiting expression of pax6—a key regulator of eye development.  shh mRNA injection into surface fish embryos produces eyeless surface fish adults (bottom right).  The lenses in these shh overexpression fish undergo apoptosis.

References

Protas, P., Jeffery, W.R. Evolution and development in cave animals: from fish to crustaceans. WIREs Dev Biol, 2012, 1:823-845.

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