Approximately 300 genes are identified that are involved in coding ECM proteins in mammals by searching domains characteristic to ECM molecules through the whole genome sequence [52]. The total number of ECM molecules corresponds to about 1.5% of proteasomes, a list of all proteins expressed by the genome. ECM proteins typically consist of repeated domains, which are coded in Ibrutinib mouse the genome as separate

exonic units and evolve through multiple processes such as exon duplication and shuffling, and gene duplication and conversion [53] and [54]. Analyses of the genomes in different organisms suggest that some ECM molecules in mammals retain ancient forms, which are found in all metazoans, while some are derived from newer proteins. Mineralization is one of the hallmark processes that has taken place during vertebrate evolution. Three major mineralized tissues, enamel, dentin, and bone, have evolved over 500 million years likely from a common ancestral process [55]. The genes for enamel matrix proteins expressed Trichostatin A datasheet by ameloblasts, AMEL, ENAM, AMBN, AMTN, and Apin/ODAM, have evolved from a common ancestral gene encoding an SCPP [56] and [57]. Enamel matrix genes are clustered on human chromosome 4q13. However, AMEL is located on sex chromosomes. AMELX and AMELY are located on the X and Y chromosomes, respectively. About 90% of the AMEL transcripts are expressed on the X locus. SCPP family genes are also mapped on

human chromosome 4. Analysis of the enamel matrix genes in different species has shown that ENEM is the most ancient gene and the other four enamel genes are derived from ENEM. AMEL is derived from AMBN and was later translocated to sex chromosomes [57]. The chromosomal synteny of these genes is conserved in primates and rodents. In birds, which lost their teeth about 100 million years ago, the enamel matrix gene cluster is lacking [58]. Initially, enamel

matrices were identified as enamel-specific molecules. However, the expression of enamel matrix proteins has been shown in other tissues outside of the tooth germ as a result of improved sensitivity in detection analyses. Furthermore, the overexpression or knockdown of these matrices not only causes enamel Oxymatrine defects, but also aberrant tooth roots, bone formation, and tumor phenotypes. The enamel matrix proteins are evolutionally related, but have distinct functions. The newly identified activities of enamel matrix proteins will provide a better understanding of the mechanisms of craniofacial development, including enamel, dentin, and craniofacial bone formation. This work was supported by grants-in-aid (20679006 to S.F., 21792054 to A.Y., 21792154 to E.F.) from the Ministry of Education, Science, and Culture of Japan, the NEXT program (LS010 to S.F.), and by grants from the Intramural Program of National Institute of Dental and Craniofacial Research, National Institutes of Health to Y.Y.