Man is but a worm: chordate origins

Area of Science:

• Zoology
• Developmental Biology
• Evolutionary Biology

Background:

• The evolutionary origin of chordates remains a significant challenge in zoology.
• Chordates possess a unique body plan that emerged from a deuterostome ancestor prior to the Cambrian period.
• Phylogenetics and developmental gene expression data have reshaped understanding of deuterostome relationships.

Purpose of the Study:

• To investigate the evolutionary origin of chordates using molecular and developmental data.
• To propose a new hypothesis for chordate ancestry based on comparative gene expression.
• To re-evaluate the body plan evolution of early chordates.

Main Methods:

• Analysis of phylogenetics and comparative developmental gene expression data.
• Examination of gene families and networks involved in body axis specification (anterior-posterior, dorsal-ventral, left-right).
• Focus on signaling pathways such as Hox gene clusters, Wnt, BMP, and nodal signaling.

Main Results:

• Chordates share gene families and networks for body axis specification with other deuterostomes.
• Anterior-posterior axis establishment is conserved among deuterostomes.
• The dorsal-ventral axis in chordates is inverted compared to other invertebrates but utilizes similar BMP pathway components.
• Left-right asymmetry is regulated by nodal signaling across diverse deuterostomes.

Conclusions:

• Chordate ancestors were likely worm-like deposit or filter feeders.
• The expansion of BMP signaling in dorsal-ventral patterning may have facilitated the evolution of key chordate features like pharyngeal gill slits.
• Early chordates possessed an anterior, tripartite, unsegmented neurosensory region.