Genetic similarity between humans and zebrafish
This study investigated whether a gene that is involved in the development of craniofacial malfunctions in humans has the same function in zebrafish. The complete genetic composition (the genome) of zebrafish is already known, which means it can be studied whether this specific gene also plays a role in the development of the skeleton in zebrafish. It turns out that this is indeed the case: if the gene is modified, it also causes malformations in the development of the facial skeleton.
“Using CRISPR-Cas9 (a special type of ‘scissors’ for cutting DNA) we have modified a gene in zebrafish that is mutated in patients with craniofacial malformations, such as cleft lip or cleft palate. Humans and zebrafish are evolutionary linked, but we still had to show that this gene has retained a similar function over time in both organisms. That turns out to be the case. So malformations in skeletal development are related to this gene”, according to Raterman.
How do you study abnormalities in skeletal development?
Raterman explains: “Right after fertilisation of the fish egg, we inject it with a CRISPR-Cas9 mix using a very small needle. It contains a recipe for where a mutation should be made in the DNA of the fish. We have made a targeted mutation by making a cut in the DNA that then repairs itself. In this way, small disruptions can occur in the gene, which can tell us something about the function of that gene.”
The injected fish does not suffer from the modification of the DNA. Two generations after the injection, there is a usable, stable mutant line in which the resulting malformations can be studied. “If we have such a mutant line, we compare the skeletal development of the fish with the mutation with that of ‘normal fish’. We do that when they are five days old. The zebrafish are still transparent at this age, so by staining we can see through the soft tissues and identify minor malformations in the skeletal formation process.”
Juriaan Metz adds: “Molecular techniques allow us to find out what causes the malformations. This provides important information about the complex processes behind the formation of the skeleton. If something goes wrong early in the development, this has consequences for the rest of life, for example for food intake or swimming behaviour.”