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Published on: January 12, 2015
Amphioxus mouth after dorso-ventral inversion.
Takao Kaji1, James D Reimer2, Arseniy R Morov3
1Department of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-hiroshima, Hiroshima 739-8526 Japan ; Present address: Department of Diabetes Technology, Graduate School of Biomedical Engineering, Tohoku University, 6-6-12 Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi 980-8579 Japan.
The amphioxus mouth develops uniquely via a mesodermal coelomic vesicle, sharing evolutionary origins with ambulacrarian pore-canals. This suggests at least three deuterostome mouth types, with chordate mouths possibly linked to early chordate body plan changes.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Zoology
Background:
- Deuterostomes typically develop mouths independently of the blastopore.
- The homology of mouths across deuterostome groups remains largely unknown.
- Amphioxus exhibits unusual lateral mouth development, unexplained by evolutionary context.
Purpose of the Study:
- To investigate the developmental process of the amphioxus mouth.
- To determine if the amphioxus mouth is a novel acquisition.
- To understand the relationship and differences between amphioxus mouths and those of other deuterostomes.
Main Methods:
- Studied the developmental process of the amphioxus mouth.
- Investigated the role of the left first somite and coelomic vesicle in mouth opening.
- Analyzed the involvement of Nodal-Pitx and Bmp2/4 signaling pathways.
- Observed effects of Nodal signaling perturbation on somite symmetry and mouth development.
- Examined Bmp2/4 expression and signaling blockade effects on mouth formation.
Main Results:
- A mesodermal coelomic vesicle, associated with the Hatschek nephridium, is crucial for amphioxus mouth opening.
- Asymmetrical development of anterior somites, regulated by Nodal-Pitx signaling, is essential for mouth formation.
- Perturbation of Nodal signaling resulted in symmetric somites and larvae lacking orobranchial structures.
- The coelomic vesicle expressed bmp2/4, and blocking this signaling prevented mouth opening.
Conclusions:
- The amphioxus mouth, involving a unique mesodermal coelomic vesicle, shares evolutionary origins with ambulacrarian coelomic pore-canals.
- At least three distinct types of mouths exist within deuterostomes.
- The acquisition of chordate mouths is likely associated with the dorso-ventral inversion in the chordate ancestor.
