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Three and Four-Dimensional Visualization and Analysis Approaches to Study Vertebrate Axial Elongation and Segmentation

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Amphioxus and the evolution of head segmentation.

Linda Z Holland¹, Nicholas D Holland, Edwin Gilland

¹*Marine Biology Research Division, Scripps Institution of Oceanography, University of California-San Diego, La Jolla CA 92093-0202, USA; Department of Anatomy, Howard University College of Medicine, 520 W Street NW, Washington, DC 20059, USA.

Integrative and Comparative Biology

|June 15, 2011

Summary

This summary is machine-generated.

The vertebrate head

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Area of Science:

Evolutionary developmental biology
Comparative genomics
Craniate evolution

Background:

The segmentation of the vertebrate head has been debated for over 150 years.
Segmentalist theories propose head segmentation evolved from amphioxus-like ancestors.
Antisegmentalists argue for an unsegmented vertebrate head or loss of segmentation before vertebrate origins.

Purpose of the Study:

To investigate the evolutionary origins of vertebrate head segmentation.
To reconcile morphological and molecular data on head development.
To clarify the ancestral state of cranial mesoderm segmentation.

Main Methods:

Comparative analysis of classical morphological studies.
Examination of developmental gene expression patterns in amphioxus and vertebrates.
Re-evaluation of theoretical conclusions based on new evidence.

Main Results:

Morphological studies confirm classical findings but challenge theoretical conclusions.
Gene expression studies reveal conserved anterior-posterior patterning mechanisms.
Homologs of amphioxus somite genes are found in lamprey head cavities and vertebrate muscles.

Conclusions:

Molecular data support an evolutionary scenario where lamprey and shark cranial paraxial mesoderm derive from amphioxus-like somites.
Bony vertebrates have lost mesodermal head segments, but remnants persist in eye and jaw muscles.
The study provides new insights into the evolution of vertebrate head segmentation.