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Developmental mechanisms for retinal degeneration in the blind cavefish Astyanax mexicanus
Author(s) -
Alunni Alessandro,
Menuet Arnaud,
Candal Eva,
Pénigault JeanBaptiste,
Jeffery William R.,
Rétaux Sylvie
Publication year - 2007
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.21488
Subject(s) - biology , retina , pax6 , eye development , sonic hedgehog , hedgehog , retinal degeneration , neuroscience , retinal , microbiology and biotechnology , genetics , gene , signal transduction , transcription factor , biochemistry
The sighted surface‐dwelling (surface fish, SF) and the blind cave‐living (cavefish, CF) forms of Astyanax mexicanus offer a unique opportunity to study the evolutionary changes in developmental mechanisms that lead to retinal degeneration. Previous data have shown the role of increased midline Sonic Hedgehog (Shh) signalling in cavefish eye degeneration (Yamamoto et al. [2004] Nature 431:844–847). Here, we have compared the major steps of eye development in SF and CF between 14 hours and 5 days of development. We have analyzed cell proliferation through PCNA and phospho‐histone H3 staining and apoptosis through TUNEL and live LysoTracker analysis. We have assessed the expression of the major eye development signalling factors Shh and Fgf8, and the eye patterning genes Pax6 , Lhx2 , Lhx9 , and Vax1 , together with the differentiation marker GAD65 . We show that eye development is retarded in CF and that cell proliferation in CF retina is proportionately similar to SF during early development, yet the retina degenerates after massive apoptosis in the lens and widespread cell death throughout the neuroretina. Moreover, and surprisingly, the signalling, patterning, and differentiation processes leading to the establishment of retinal layers and cell types happen almost normally in CF, although some signs of disorganization, slight heterochronies, and a lack of expression gradients are observable. Our data demonstrate that the evolutionary process of eye degeneration in the blind CF does not occur because of patterning defects of the retina and are consistent with the proposed scenario in which the trigger for eye degeneration in CF is lens apoptosis. J. Comp. Neurol. 505:221–233, 2007. © 2007 Wiley‐Liss, Inc.