Tracing the evolutionary origin of vertebrate skeletal tissues: insights from cephalochordate amphioxus.
Vertebrate mineralized skeletal tissues are widely considered as an evolutionary novelty. Despite the importance of these tissues to the adaptation and radiation of vertebrate animals, the evolutionary origin of vertebrate skeletal tissues remains largely unclear. Cephalochordates (Amphioxus) occupy a key phylogenetic position and can serve as a valuable model for studying the evolution of vertebrate skeletal tissues. Here we summarize recent advances in amphioxus developmental biology and comparative genomics that can help to elucidate the evolutionary origins of the vertebrate skeletal tissues and their underlying developmental gene regulatory networks (GRN). By making comparisons to the developmental studies in vertebrate models and recent discoveries in paleontology and genomics, it becomes evident that the collagen matrix-based connective tissues secreted by the somite-derived cells in amphioxus likely represent the rudimentary skeletal tissues in chordates. We propose that upon the foundation of this collagenous precursor, novel tissue mineralization genes that arose from gene duplications were incorporated into an ancestral mesodermal GRN that makes connective and supporting tissues, leading to the emergence of highly-mineralized skeletal tissues in early vertebrates.
Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 11529, Taiwan.
Luok Wen
LW
Yong
Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 11529, Taiwan. Electronic address: jkyu@gate.sinica.edu.tw.
Jr-Kai
JK
Yu
D000818:Animals; D001846:Bone Development / Q000235:genetics*; D043344:Chordata / Q000235:genetics / Q000254:growth & development; D015509:Developmental Biology; D019143:Evolution, Molecular; D053263:Gene Regulatory Networks / Q000235:genetics; D064175:Lancelets / Q000235:genetics* / Q000254:growth & development; D008648:Mesoderm / Q000254:growth & development / Q000378:metabolism; D014714:Vertebrates / Q000235:genetics*