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Precraniate origin of cranial motoneurons
Héloïse D Dufour1, Zoubida Chettouh, Carole Deyts
1Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8542, Ecole Normale Supérieure, 46 Rue d'Ulm, 75005 Paris, France.
Summary
Cranial motoneurons, previously of unclear origin, are homologous to ascidian motoneurons. This finding suggests the vertebrate hindbrain evolved before the origin of craniates, pushing back cranial nerve evolution.
Area of Science:
- Evolutionary developmental biology
- Neuroscience
- Comparative genomics
Background:
- Cranial sensory neurons in craniates originate from neurogenic placodes and neural crest.
- The phylogenetic origin of cranial motoneurons in the hindbrain remains unclear.
Purpose of the Study:
- To determine the phylogenetic status of cranial motoneurons.
- To investigate the evolutionary origins of the vertebrate hindbrain and cranial nerves.
Main Methods:
- Comparative analysis of gene expression in ascidian (Ciona intestinalis) and vertebrate motoneurons.
- Identification of conserved transcription factors (CiPhox2, CiTbx20, CiHox1) in ascidian hindbrain development.
Main Results:
- Ascidian postmetamorphic motoneurons express transcription factors homologous to vertebrate cranial motoneurons (CiPhox2, CiTbx20).
- These ascidian motoneurons originate from a hindbrain region marked by CiPhox2 and CiHox1, similar to vertebrates.
- The ascidian brain structure corresponds to the vertebrate hindbrain.
Conclusions:
- Ascidian postmetamorphic motoneurons are homologous to vertebrate cranial motoneurons.
- The vertebrate hindbrain is an ancient structure, predating the origin of craniates.
- The evolutionary origin of cranial nerves predates the emergence of craniates.
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