Enamel First Evolved in Skin and Only Colonized Teeth Much Later

When did the enamel that covers our teeth evolve? And where in the body did this tissue first appear? In an article published online on September 23, 2015 in Nature, researchers from Uppsala University in Sweden and the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) in Beijing, China, combine data from two very different research fields, paleontology and genomics, to arrive at a clear but unexpected answer to this question: enamel originated in the skin and colonized the teeth much later. The Nature article is titled “New Genomic and Fossil Data Illuminate the Origin of Enamel.” We are all familiar with enamel. It is shiny and white; this tissue gleams back at us from the bathroom mirror every morning when we brush our teeth. It is the hardest substance produced by the body, composed almost entirely of the mineral apatite (calcium phosphate) deposited on a substrate of three unique enamel matrix proteins. Like other land vertebrates we only have teeth in the mouth, but certain fishes such as sharks also have "dermal denticles" - little tooth-like scales - on the outer surface of the body. In many fossil bony fishes, and a few archaic living ones such as the gar (Lepisosteus) from North America, the scales are covered with an enamel-like tissue called "ganoine." Dr. Tatjana Haitina, a researcher in the Department of Organismal Biology, Uppsala University, investigated the genome of Lepisosteus, which was sequenced by the Broad Institute, and found that it contains genes for two of our three enamel matrix proteins: the first to be identified from a ray-finned bony fish. Furthermore, these genes are expressed in the skin, strongly suggesting that ganoine is a form of enamel. But where did enamel originate - in the mouth, in the skin, or both at once?
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