Zhang Guangjun, Cohn Martin J
Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611, USA.
Proc Natl Acad Sci U S A. 2006 Nov 7;103(45):16829-33. doi: 10.1073/pnas.0605630103. Epub 2006 Oct 31.
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 (Col2alpha1), whereas that of jawless fishes has long been thought to be noncollagenous. We recently showed that Col2alpha1 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 Col2alpha1-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.
脊椎动物的起源是由骨骼的进化所定义的；然而，对于促成这一具有里程碑意义的进化创新的发育机制，我们却知之甚少。在有颌脊椎动物中，软骨基质主要由II型胶原蛋白（Col2alpha1）组成，而长期以来人们一直认为无颌鱼类的软骨基质是非胶原性的。我们最近发现七鳃鳗的软骨中存在Col2alpha1，这表明基于II型胶原蛋白的软骨进化得比之前认为的更早。在此，我们研究脊椎动物软骨的起源，并报告盲鳗（七鳃鳗的姐妹类群）也有基于Col2alpha1的软骨，这表明其存在于冠群脊椎动物的共同祖先中。我们进一步表明，文昌鱼（脊椎动物的姐妹类群）拥有一个在脊索中表达的祖先A类原纤维胶原蛋白（ColA）基因。这些结果共同表明，在脊索动物 - 脊椎动物过渡阶段ColA基因的复制和多样化可能是脊椎动物骨骼组织进化起源的基础。
