Molecular decay of enamel-specific gene in toothless mammals supports theory of evolution

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Washington, September 4 (ANI): Biologists at the University of California, Riverside have found molecular decay of enamel-specific gene in toothless mammals, which provides fresh support for Charles Darwin's theory of evolution.

The researchers were able to correlate the progressive loss of enamel in the fossil record with a simultaneous molecular decay of a gene, called the enamelin gene, which is involved in enamel formation in mammals.

Enamel is the hardest substance in the vertebrate body, and most mammals have teeth capped with it.

Examples exist, however, of mammals without mineralized teeth (e.g., baleen whales, anteaters, pangolins) and of mammals with teeth that lack enamel (e.g., sloths, aardvarks, and pygmy sperm whales).

Further, the fossil record documents when enamel was lost in these lineages.

"The fossil record is almost entirely limited to hard tissues such as bones and teeth," said Mark Springer, a professor of biology, who led the study.

"Given this limitation, there are very few opportunities to examine the co-evolution of genes in the genome of living organisms and morphological features preserved in the fossil record," he added.

In 2007, Springer, along with Robert Meredith and John Gatesy in the Department of Biology at UC Riverside, initiated a study of enamelless mammals in which the researchers focused on the enamelin gene.

They predicted that these species would have copies of the gene that codes for the tooth-specific enamelin protein, but this gene would show evidence of molecular decay in these species.

"Mammals without enamel are descended from ancestral forms that had teeth with enamel," Springer said.

"We predicted that enamel-specific genes such as enamelin would show evidence in living organisms of molecular decay because these genes are vestigial and no longer necessary for survival," he added.

Now, his lab has found evidence of such molecular "cavities" in the genomes of living organisms.

Using modern gene sequencing technology, Meredith discovered mutations in the enamelin gene that disrupt how the enamelin protein is coded, resulting in obliteration of the genetic blueprint for the enamelin protein.

Darwin argued that all organisms are descended from one or a few organisms and that natural selection drives evolutionary change.

The fossil record demonstrates that the first mammals had teeth with enamel. Mammals without enamel therefore must have descended from mammals with enamel-covered teeth.

"We could therefore predict that nonfunctional vestiges of the genes that code for enamel should be found in mammals that lack enamel," Springer said. (ANI)

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