rationalskepticism.org

Calilasseia wrote:

From the latter paper about Hedgehog signalling, I provide the abstract:

Yamamoto [i]et al[/i], 2004 wrote:Hedgehog (Hh) proteins are responsible for critical signalling events during development but their evolutionary roles remain to be determined. Here we show that hh gene expression at the embryonic midline controls eye degeneration in blind cavefish. We use the teleost Astyanax mexicanus, a single species with an eyed surface-dwelling form (surface fish) and many blind cave forms (cavefish), to study the evolution of eye degeneration. Small eye primordia are formed during cavefish embryogenesis, which later arrest in development, degenerate and sink into the orbits. Eye degeneration is caused by apoptosis of the embryonic lens, and transplanting a surface fish embryonic lens into a cavefish optic cup can restore a complete eye. Here we show that sonic hedgehog (shh) and tiggy-winkle hedgehog (twhh) gene expression is expanded along the anterior embryonic midline in several different cavefish populations. The expansion of hh signalling results in hyperactivation of downstream genes, lens apoptosis and arrested eye growth and development. These features can be mimicked in surface fish by twhh and/or shh overexpression, supporting the role of hh signalling in the evolution of cavefish eye regression.

So it transpires that if you transplant an embryonic lens taken from a surface-dwelling Astyanax mexicanus with normal eyes into the optic cup of an embryonic blind cavefish, normal eye development resumes. Interesting is it not? And, by manipulating the shh and twhh gene expression in surface-dwelling eyed fishes during embryonic development, the scientists were able to reproduce the eye apoptosis seen in the cave dwelling fishes.