WEISS, K.M.; KAWASAKI, K; SHOLTIS, S; Penn State University: Evolutionary genetics of dental development: teeth as part of vertebrate structural organisation.

Vertebrate mineralized tissues are in part the product of the expansion history of a cluster of secretory calcium-binding phosphoprotein (SCPP) genes. These genes are important in bone and tooth mineralization. The SCPP gene family helps assign ontology and evolutionary identity to amelogenin, the only member gene not in the main cluster. Phylogenetic reconstruction is possible because of the structural nature of the SCPP genes, even though they have little sequence homology. Interestingly, though basically maintaining tandem cluster organization, enamel matrix and bone/dentine protein SCPP genes are expressed in opposing tissues, as in dental epithelium and mesenchyme, and in physically close but functionally unrelated structures (salivary glands), suggesting interesting but as yet unknown regulatory control mechanisms. Independent and somewhat parallel expansions have occurred in tetrapod and teleost lineages, perhaps answering some basic questions about the origins of vertebrate exo- and endoskeletal tissues such as enamel and enameloid, including structures and processes derived for the protection of the young (eggshell and milk). Dentition patterning genes expressed in tooth development appear to regulate relevant SCPP genes as downstream targets, probably indirectly, tentatively closing a developmental circle for the dentition.