Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 45, Pages 16829-16833Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0605630103
Keywords
development; gene duplication; skeleton evolution; chordate; notochord
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The origin of vertebrates was defined by evolution of a skeleton; however, little is known about the developmental mechanisms responsible for this landmark evolutionary innovation. In jawed vertebrates, cartilage matrix consists predominantly of type II collagen (Col2 alpha 1), whereas that of jawless fishes has long been thought to be noncollagenous. We recently showed that Col2 alpha 1 is present in lamprey cartilage, indicating that type II collagen-based cartilage evolved earlier than previously recognized. Here, we investigate the origin of vertebrate cartilage, and we report that hagfishes, the sister group to lampreys, also have Col2 alpha 1-based cartilage, suggesting its presence in the common ancestor of crown-group vertebrates. We go on to show that lancelets, a sister group to vertebrates, possess an ancestral clade A fibrillar collagen (ColA) gene that is expressed in the notochord. Together, these results suggest that duplication and diversification of C6lA genes at the chordate-vertebrate transition may underlie the evolutionary origin of vertebrate skeletal tissues.
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