Decay at the molecular level of genes regulating enamel in toothless animals

University of California biologists have reported new evidence of evolutionary changes found in today's fossil and genome data, once again proving Darwin's theory of evolution.

Scientists have linked the process of losing enamel in fossil data with molecular decay of the enamelin gene, a gene involved in the formation of enamel in mammals.

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

However, there are also mammals that do not have mineralized teeth (for example, horned whales, ants, pangolins) and also toothed animals that do not have enamel (eg, lazy , pig, small sperm whale).Fossil evidence has revealed exactly when tooth enamel has disappeared in these species.

'Fossil data is almost confined to hard tissues like bones and teeth,' said Mark Springer, a biology lecturer, lead researcher. 'With this limitation, there is little chance for us to examine the development of the existing genes in the organisms of today and the morphological characteristics stored in fossils.'

In 2007, Springer and Robert Meredith and John Gatesy from the California Department of Biology at Riverside began a survey of enameled animals, focusing on the enamelin gene. They predict that these species will have copies of the gene encoded for enamelin that regulate teeth, and these copies will be evidence of gene degradation at the molecular level.

'Non-enameled animals have ancestors that have teeth and tooth enamel,' said Pringer. 'We predict that in today's animals, we will find evidence that enamel regulation genes such as enamelin, for example, are degraded at the molecular level, and these genes only exist. as a trail of ancient characteristics, they are no longer necessary for the animal's existence. '

Now his lab has found evidence of these molecular holes in today's animal genomes. With the use of modern gene sequencing technologies, Meredith discovered that the changes in the enamelin gene disrupted the enamelin protein coding process, resulting in the destruction of the gene scheme for the enamelin protein.

Ancient baleen whale, such as Aetiocetus weltoni, lived 25 million years ago (pictured above), once had teeth and enamel. But today's horned whales (below) do not have teeth and live on food as tiny organisms are filtered through their jaws. Although there are no teeth, the horny whales today retain a copy of the teeth regulation genes, such as the enamelin gene; these redundant genes are inherited from their ancestors with teeth and are evidence of mutant decline in accordance with the content of evolutionary theory. (Photo: © John Gatesy and Carl Buell.)

The findings were published in PLoS Genetics on September 4.
Darwin theorized that all organisms originated from one or several organisms, and that the natural choice motivated changes in evolution. Fossil data demonstrate that the first mammals have teeth with tooth enamel. Therefore, enamel-free animals today certainly evolved from toothed animals with full enamel.

'Therefore, we can predict that the remaining traces of the enamel-coding genes will be found on enamel-free animals,' Springer said. 'However, when we made predictions, we did not have enamelin gene sequences in non-toothed animals as well as non-enameled animals. Therefore, our laboratory focuses on finding these gene sequences so that we can test our predictions. '

Previous studies in evolutionary biology provided only limited evidence of the relationship between morphological degeneration in fossil data with molecular degradation at the molecular level. The Springer team's research took advantage of the hardness of teeth and enamel to provide clearer evidence of this connection.

'In the study, we clearly see the parallel development of the enamel loss process in fossil data and the molecular decay of the enamelin gene into a pseudogene in the representatives of four Different mammals have lost tooth enamel. '

In general, the study divided into the following steps: First, Meredith collected DNA sequences for the enamelin gene in different animals. The team then analyzed these sequences with various methods of molecular evolution, including new approaches invented by the team.Finally, they use analytical results to test the old hypotheses as well as make new hypotheses.

'Currently, we are actively decoding the evolutionary history of genes other than enamelin that are involved in tooth enamel formation,' Springer said.