DNA sequence enhances our understanding of the origins of jaws
All vertebrates live on land, and all have jaws, so they are a member of the jawed vertebrate group. Humans are an example of this kind of animal.
The development of a pair of teeth and the subsequent opening of the mouth was a critical step in the transformation of early vertebrates into animals with a skeleton and a circulatory system.
During the evolution of mammals, this moved to the middle ear to enhance hearing and was replaced by the secondary jaw joint, which is how humans are built today.
The primary jaw joint has an active gene which contains sequence information for a specific protein.
The evolution of this jaw joint has long been thought to have been aided by this protein, but little is known about how it is regulated in the jaw joint cells.
Genes are activated with help from enhancers that don't contain information about genes. The "regulatory" DNA can contribute to the activation of the gene only in a certain cell type and can be found in different animal species.
The "regulatory" DNA can contribute to the activation of the gene only in a certain cell type and can be found in different animal species.
We searched through the genome sequences of many different vertebrate species and only found the DNA sequence near the Nkx3.2 gene in jawed vertebrates—not in jawless ones.
We injected these DNA sequences from jawed vertebrates into zebrafish embryos. They all activated in jaw joint cells.
Their ability to activate has been preserved for more than 400 million years shows just how important it is for jawed vertebrates.
Experiments were conducted where the newly discovered DNA sequence was deleted from the zebrafish genome using the CRISPR/Cas9 technique.
Some kind of regulatory defect was later repaired, suggesting that there is additional DNA somewhere in the genome that controls the activation of the Nkx3.2 gene and is waiting to be discovered.
Their discovery is an important step towards eventually understanding the process behind the origins of vertebrate jaws.