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SCPP genes in the coelacanth: Tissue mineralization genes shared by sarcopterygians
Author(s) -
Kawasaki Kazuhiko,
Amemiya Chris T.
Publication year - 2014
Publication title -
journal of experimental zoology part b: molecular and developmental evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.823
H-Index - 63
eISSN - 1552-5015
pISSN - 1552-5007
DOI - 10.1002/jez.b.22546
Subject(s) - vertebrate , biology , evolutionary biology , enamel paint , gene , genetics , medicine , dentistry
The coelacanth is the basal‐most extant sarcopterygian that has teeth and tooth‐like structures, comprising bone, dentin, and enamel or enameloid. Formation of these tissues involves many members of the secretory calcium‐binding protein (SCPP) family. In tetrapods, acidic‐residue‐rich SCPPs are used in mineralization of bone and dentin, whereas Pro/Gln‐rich SCPPs participate in enamel formation. Teleosts also employ many SCPPs for tissue mineralization. Nevertheless, the repertoire of SCPPs is largely different in teleosts and tetrapods; hence, filling this gap would be critical to elucidate early evolution of mineralized tissues in osteichthyans. In the present study, we searched for SCPP genes in the coelacanth genome and identified 11, of which two have clear orthologs in both tetrapods and teleosts, seven only in tetrapods, and two in neither of them. Given the divergence times of these vertebrate lineages, our discovery of this many SCPP genes shared between the coelacanth and tetrapods, but not with teleosts, suggests a complicated evolutionary scheme of SCPP genes in early osteichthyans. Our investigation also revealed both conserved and derived characteristics of SCPPs in the coelacanth and other vertebrates. Notably, acidic SCPPs independently evolved various acidic repeats in different lineages, while maintaining high acidity, presumably important for interactions with calcium. Furthermore, the three Pro/Gln‐rich SCPP genes, required for mineralizing enamel matrix and confirmed only in tetrapods, were all identified in the coelacanth, strongly suggesting that enamel is equivalent in the coelacanth and tetrapods. This finding corroborates the previous proposition that true enamel evolved much earlier than the origin of tetrapods. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 390–402, 2014 . © 2013 Wiley Periodicals, Inc.