How are things going with the ‘minigenes USH2c’ study?

By now, the USH2c minigenes study was started almost a year ago. A four-year study which was made possible by co-financing of the Stichting Ushersyndroom, CUREUsher and LSBS. Thanks to many contributors this study was started early in the year 2020 in the research group of Erwin van Wijk, in the Radboudumc. Merel Stemerdink is working as a doctoral candidate on the development of a minigene therapy for USH2c. In this news report, Merel tells more about the progress that she has been able to make with respect to the study during the past year! 

Merel in the aquarium holding the tank in which the USH2c zebrafishes are swimming.

The minigenes
USH2c is caused by mutations in the USH2c gene (ADGRV1) and these faults in the gene result in progressive hereditary deafblindness. In the eye these faults make the retina slowly die. The objective of the project is to develop a minigene therapy specifically for treating this retina degeneration. 

What makes the development of a therapy a challenge is that the ADGRV1 gene is really big, so big that it cannot be packed in the ‘lorry’ (‘viral vector) that is to deliver a new, healthy copy of the gene at the correct place in the retina. This is the reason why we are making an artificial short version of the ADGRV1 gene. These minigenes will be small enough to fit in a ‘viral vector’, but at the same time the minigenes have to function well enough to make good the negative effect of the mutations in the ADGRV1 gene. 

Based on various bioinformatics analyses we have developed four ADGRV1 minigenes. These minigenes contain the most important pieces of the healthy ADGRV1 gene. In the past year, we managed to isolate all these individual pieces of ADGRV1 and I will start assembling these parts and so eventually make the minigenes in the coming months. However, this obviously is not all: after this we will study whether these minigenes are actually able to take over the function of the mutant ADGRV1 gene.  

Zebrafishes with USH2c
In order to test the therapeutic effect of minigenes, we made an USH2c zebrafish last year. Zebrafishes also have the ADGRV1 gene and we see with healthy zebrafishes that ADGRV1 is expressed in the retina, just as with humans. By means of CRISPR/Cas-9 technology, we deliberately made small faults in the ADGRV1 gene of zebrafishes so as to simulate the disease in the fish. Last month was really exciting, as we started the first experiments to see of the faults made in the gene really prevent the ADGRV1 protein from being produced in the eyes of the USH2c zebrafishes and this appeared to be the case indeed! In the coming year, we will do additional research in order to get a complete picture of the visual function of this USH2c zebrafish. This is important because this will be the basis of the testing of the minigenes in the USH2c zebrafishes so as to allow us to see if and to what extent the minigenes are able to recover the functioning of the retina. 

This means that the first important steps were taken in the past year: the minigenes have been developed and the first results indicate that we have developed a zebrafish model suitable for testing the minigenes! 

Do you have any questions about the study further to this news report? You can contact Merel via the mail.

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