Prox 1 in eye degeneration and sensory organ compensation during development and evolution of the cavefish Astyanax

We have investigated expression of the homeobox gene Prox 1 during eye dege neration and sensory organ compensation in cavefish embryos. The teleost As tyanax mexicans consists of sighted surface-dwelling forms (surface fish) a nd several populations of blind cave-dwelling forms (cavefish), which have evolved independently. Eye formation is initiated during cavefish developme nt, but the lens vesicle undergoes apoptosis, and the eye subsequently atte sts and degenerates. The requirement of Prox 1 for lens fiber differentiati on and gamma-crystallin expression in the mouse suggests that changes in th e expression of this gene could be involved in cavefish eye degeneration, S urface fish and cavefish embryos stained with a Prox 1 antibody showed Prox 1 expression in the lens, neuroretina, myotomes, heart, hindbrain, and gut , as reported in other vertebrates. We found that Prox 1 expression is not altered during cavefish lens development. Prox 1 protein was detected in th e lens vesicle as soon as it formed and persisted until the time of lens de generation in each cavefish population. The cavefish lens vesicle was also shown to express a gamma-crystallin gene, suggesting that Prox 1 is functio nal in cavefish lens development. In addition to the tissues described abov e, Prox 1 is expressed in developing taste buds and neuromasts in cavefish, which are enhanced to compensate for blindness. It is concluded that the P rox 1 gene is not involved in lens degeneration, but that expansion of the Prox 1 expression domain occurs during taste bud and neuromast development in cavefish.