Type II collagen-based cartilage evolved in stem vertebrates

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Type II collagen-based cartilage evolved in stem vertebrates

Postby Anonymous » Wed Nov 01, 2006 7:53 am

http://www.pnas.org/cgi/content/abstrac ... 103v1?etoc

Hagfish and lancelet fibrillar collagens reveal that type II collagen-based cartilage evolved in stem vertebrates

GuangJun Zhang and Martin J. Cohn

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 ColA genes at the chordate-vertebrate transition may underlie the evolutionary origin of vertebrate skeletal tissues.

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