Hedgehog signalling controls eye degeneration in blind cavefish

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genetics

Background:

• Hedgehog (Hh) proteins are crucial for embryonic development.
• The evolutionary role of Hh signaling in adaptation, particularly eye loss, is not well understood.

Purpose of the Study:

• To investigate the role of Hh gene expression in the evolutionary degeneration of eyes in blind cavefish.
• To identify the genetic mechanisms underlying eye loss in the Astyanax mexicanus species complex.

Main Methods:

• Comparative analysis of gene expression in eyed surface fish and blind cavefish.
• Embryonic eye development observation and lens apoptosis assessment.
• Gene overexpression experiments in surface fish models.

Main Results:

• Blind cavefish exhibit expanded sonic hedgehog (shh) and tiggy-winkle hedgehog (twhh) gene expression at the embryonic midline.
• This expanded Hh signaling leads to lens apoptosis and arrested eye development in cavefish.
• Overexpression of twhh and/or shh in surface fish mimics the eye degeneration phenotype observed in cavefish.

Conclusions:

• Aberrant Hh signaling is a primary driver of eye degeneration during cavefish evolution.
• The study provides a genetic basis for the loss of eyes in cave-dwelling vertebrates.
• Hh pathway modulation represents a significant evolutionary adaptation in response to subterranean environments.