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Expanded expression of Sonic Hedgehog in Astyanax cavefish: multiple consequences on forebrain development and
Arnaud Menuet1, Alessandro Alunni, Jean-Stéphane Joly
1CNRS-UPR2197 DEPSN, Institut Fessard, Avenue de la Terrasse, 91198 Gif-sur-Yvette cedex, France.
Development (Cambridge, England)
|January 26, 2007
Summary
Enhanced Sonic Hedgehog (Shh) signaling in cavefish forebrain development influences neuronal patterning. This developmental shift impacts olfactory and hypothalamic regions, contributing to evolutionary diversity.
Area of Science:
- Developmental biology
- Evolutionary biology
- Neuroscience
Background:
- Ventral midline Sonic Hedgehog (Shh) signaling is essential for embryonic forebrain development.
- Astyanax mexicanus, a blind cavefish, provides a model to study forebrain evolution compared to surface dwellers.
Purpose of the Study:
- Investigate the impact of enhanced Shh midline signaling on telencephalic and diencephalic neuronal patterning in cavefish.
- Compare forebrain development between cave and surface Astyanax mexicanus.
Main Methods:
- Comparative analysis of Shh expression patterns during development in cave and surface Astyanax.
- Examination of specific neuronal populations and gene expression (Nkx2.1a, Nkx2.1b, Lhx6, Lhx7, GABA).
- Assessment of cell proliferation and migratory pathway development.
Main Results:
- Cavefish exhibit increased Shh expression in anterior midline domains throughout development.
- Expanded Nkx2.1a expression and heightened cell proliferation observed in the cavefish basal diencephalon and hypothalamus.
- An enlarged Nkx2.1b-Lhx6-GABA migratory pathway to the olfactory bulb and altered Lhx7 expression in the basal forebrain were found in cavefish.
- These changes are Shh-dependent.
Conclusions:
- Enhanced Shh signaling in cavefish does not alter global forebrain regionalization but specifically impacts neuronal populations.
- Shh-dependent increases in olfactory and hypothalamic components suggest a role for telencephalic midline organizers in modulating forebrain evolution.
- This study highlights developmental mechanisms generating neuronal diversity in vertebrate forebrain evolution.
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