Evolution of the endothelin pathway drove neural crest cell diversification

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genetics

Background:

• Neural crest cells (NCCs) are vertebrate-specific migratory cells crucial for forming diverse adult features.
• Genomic events like gene duplication are hypothesized to contribute to NCC evolution, but direct functional evidence is lacking.
• Endothelin (Edn) signaling is unique to vertebrates and plays roles in NCC development in jawed vertebrates.

Purpose of the Study:

• To investigate if the evolution of Edn signaling was a driving force in the evolution of NCCs.
• To understand the ancient and lineage-specific roles of Edn signaling in NCC development.
• To link gene evolution, including duplication, to the emergence of NCCs as a vertebrate novelty.

Main Methods:

• CRISPR-Cas9 mutagenesis was used to disrupt edn, ednr, and dlx genes in the sea lamprey (Petromyzon marinus).
• Comparative analyses were performed using Xenopus laevis to expand gnathostome representation.
• Functional genetic evidence was gathered by observing the effects of gene disruption on NCC development.

Main Results:

• Edn signaling was active in NCCs prior to vertebrate genome duplication events.
• Following genome-wide duplications, paralogous Edn pathways diverged, leading to distinct NCC subpopulations with varied signaling requirements.
• Differences in Edn pathway targets correlate with variations in the oropharyngeal skeleton and autonomic nervous system between lampreys and gnathostomes.

Conclusions:

• The evolution of Edn signaling provided functional genetic links to the origin and duplication of genes driving NCC evolution.
• Divergence of Edn signaling pathways after genome duplication created developmental modularity, enabling the independent evolution of NCC derivatives.
• This study provides functional evidence for the stepwise evolution of NCCs, a defining vertebrate trait, through gene duplication and pathway diversification.