Enamel appeared in fish skin for over 400 million years – publico

                 

                         
                     

                 

 
                         

Dental enamel is the hard tissue that humans produce. Made almost completely the calcium phosphate based, which is deposited an organic matrix, this is the material that coats the teeth, covering the dentin. Although it is perfect for chewing food, its origins can be amazing. According to a new study, this tissue and the genetic apparatus required to produce have more than 400 million years. The enamel appeared in fish, just not coated teeth of those animals, appeared before in your skin.

                     

                          Over millions of years, this tissue was coating the fish head and finally also came to cover the teeth, suggests an article published yesterday in the Nature . Today, amphibians, reptiles and mammals have tooth enamel but show no trace of enamel production in the skin, demonstrating that the use of the genetic apparatus for the production of this fabric has changed completely.

In humans, the first baby teeth begin to form early in pregnancy, at 14 weeks. The deposition of the enamel is made in a protein matrix consisting of amelogenin enamelin and amelin. These three proteins are produced by ameloblasts calls cells and form a matrix that is being replaced later by calcium phosphate crystals.

Certain fish have skin stiff structures with a similar composition the teeth in vertebrates. The famous coelacanth is one such case. This living fossil is important to this story. The coelacanth is descended from a line of 400 million. At that time, coelacanths were close ancestor of tetrapods (the animal out of the water about 375 million years ago and colonized the continents giving rise to land vertebrates). As tetrapods, coelacanths have enamel on the teeth.

But it was assumed that the enamel of the teeth and stiff structure of the coelacanth’s body had arisen and evolved separately.

“In humans, the enamel is only the teeth, and it is very important to its function, so it is natural to assume that evolved there,” says paleontologist Per Erik Ahlberg of Uppsala University in Sweden, and one of the paper’s authors, quoted by Reuters. The discovery now made “is important because it’s unexpected,” says the scientist. The team left genetics and paleontology to try to unravel the origin of the enamel.

The researchers were analyzing the genome of Lepisosteus oculatus , a fish that belongs to actinopterígeos – one of the most important groups of fish, far from the coelacanths. The Lepisosteus oculatus is considered a primitive fish within the actinopterígeos. It has enamel in the teeth, but it has the skin of the body and head tissue which resembles the enamel. The latest actinopterígeos fish such as zebrafish, no longer has the substance.

The team was to analyze the Lepisosteus oculatus genes equivalent to human genes which give instructions for the production of the protein matrix, where the enamel is deposited. They found that these genes were active on the skin of the fish, and that this substance was indeed similar to enamel. What shows an evolutionary relationship.

Then the researchers were looking at the past, analyzing the scale of fossils of two species of fish that lived during the Silurian period, the Andreolepis (for there are 425 million years old, found in Sweden) and Psarolepis (of there 418 million years , discovered in China). The first had a thin layer of enamel in the body scales, but had no head or teeth. The second had enamel on the scales of the body and head, but had no enamel on the teeth.

“The Psarolepis and Andreolepis are among the oldest bony fish [the large group of fish that is different from cartilage, such as sharks and rays that do not produce enamel] ” explains Per Erik Ahlberg, quoted a statement from their university. “Therefore, we believe that the lack of enamel on teeth is due to be primitive. It seems that the enamel originated in the skin and then colonized teeth. “

From this data set, the scientists proposed a hypothesis about the emergence and evolution of enamel. The fabric first appeared in the body scales, as shown in the Andreolepis , then switched to the skull, Psarolepis is an example of this phase, and finally the tissue has advanced to the teeth, see the coelacanth.

Somehow, in the evolution of tetrapods, the enamel is no longer produced maintaining the skin only on the teeth. In the evolution of actinopterígeos, the enamel was never arise in the teeth and faded skin of the most modern fish of this group.

Looking back, the use of enamel shows how evolution is dynamic. With features that are lost or gain new functions. As Qingming Qu, another author of the study: “Despite this fabric in our teeth be used to bite or tear, it was originally used as a protective tissue, as in primitive fish.”