Schiel gene discovered?

Mutation leads to the "silver look" in zebrafish

When squinting, the eyes look in different directions. ideabug / istock
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Silberblick: Researchers may have uncovered a genetic basis for strabismus. They found that mutations in a particular gene in zebrafish lead to the malformation of an important cranial nerve. This nerve controls movements of the eyeball and therefore plays a significant role in a healthy look. Whether changes in the now identified gene in humans have similar consequences, further studies must show.

If we fix a certain object, both eyes usually look in the same direction. Each eye captures an image slightly different from that of the other eye. In the brain, these two images are then assembled into a common sensory perception.

Due to a malposition, however, it can happen that one eye deviates from the desired direction of sight: those affected squint. Untreated, this so-called "silver look" can have serious consequences - especially in childhood. Because the visual system does not develop properly in such cases, for example, visual acuity deteriorates or spatial vision is disturbed.

Investment in view

But why are some people even squinting? It is clear that in certain forms of strabismus the predisposition also plays a role. Exactly this factor has now been dedicated to scientists around Kazuhide Asakawa from the National Institute of Genetics in Mishima, Japan. They wanted to know: How do genetic mutations influence the development of the eye muscles and their controlling neurons in the brain?

To find out, they looked at zebrafish. These model organisms are almost transparent as embryos, so that their inner development from a few cells to the right fish can only be tracked with the aid of a microscope. For their study, the researchers used genetically modified animals in which the neurons controlling the eye movement and the corresponding muscles in different colors fluoresced and could thus be observed even better. display

Fluorescent proteins in the nervus abducens (green) and the eye muscles (magenta) in the zebrafish © Kazuhide Asakawa

Defective protein

They discovered that if the gene protocadherin 17 (Pcdh17) is altered, the motor neurons of the so-called abducens nerve do not develop properly - an important cranial nerve for the movement of the eyeball. As the scientists report, this genome section contains the genetic blueprint for a protein that is normally located on the cell surface of motor neurons.

If a defective protein is formed as a result of a mutation, this has fatal consequences: the nerve does not align properly in the brain and can not establish a connection to the eye muscles to which it is to forward information. The consequence of these missing motion signals can be a squint problem.

"The Pcdh17 protein is not only found in zebrafish, but also in humans. It could thus play a similar role in the human body for the development of normal eye movements, "concludes Asakawa. (Cell Reports, 2018; doi: 10.1016 / j.celrep.2018.07.024)

(Research Organization of Information and Systems, 08.08.2018 - DAL)