Instead of complete blindness – "chicken"
Scientists: gene therapy for the first time protected a mouse from developing blindness
Biologists from the USA for the first time used the CRISPR/Cas9 genomic editor to "fix" DNA in mouse retinal cells and remove a gene associated with the development of complete blindness, according to an article published in the journal Nature Communications (Yu et al., Nrl knockdown by AAV-delivered CRISPR/Cas9 prevents retinal degeneration in mice).
"Our past experiments have shown that we can avoid the development of blindness in such animals if we remove the Nrl gene in the retinal cells, which will cause the rods to turn into cells similar in shape to cones. This will save both the "former" sticks and the real cones adjacent to them from destruction in the future," explains Anand Swaroop from the National Eye Institute in Bethesda (USA).
The eyes of humans and many other mammals contain two types of light–sensitive cells - cones and rods. Cones allow us to distinguish colors, but at the same time they work only at sufficiently high illumination, and sticks allow us to see silhouettes of objects in the dim light of stars or the Moon.
According to Swarup, sticks, in addition to the work of "night vision", play another important role – they support and nourish the remaining cells of the retina, and their destruction irreversibly leads to the death of cones and the entire retina as a whole. Most of the mutations associated with vision loss usually affect the rods, and if they are present, a person usually loses first night vision, and then the ability to see the world in daylight.
Experiments on embryos that Swarup and his colleagues have conducted in the past have shown that the process of growth of rods and cones is actually controlled by one gene – Nrl. If this gene is removed during the formation of the embryo, then the retina appears, the cones in which do not die, despite the absence of rods.
Scientists have suggested that the removal of this gene in retinal cells in an adult animal will lead to similar consequences. Guided by this idea, biologists created a retrovirus based on the popular genomic editor CRISPR/Cas9, infecting only sticks and removing the Nrl gene from their DNA.
Green fluorescence indicates the expression of NRL genes in the retina of mice. At the top – normal expression, at the bottom – reduced after the removal of the NRL.
An image from the press release of NIH-funded scientists deploy CRISPR to preserve photoreceptors in mice - VM.
Biologists tested the work of this gene therapy on three groups of mice whose DNA contained different mutations leading to the destruction of rods and retinal degeneration. As these experiments have shown, the removal of the gene really led to the transformation of rods into analogues of cones, and this transformation stopped the destruction of the retina.
Eventually, the mice lost the ability to see in the dark, as all of their wands were disabled, but did not lose their vision in the daytime. According to biologists, gene therapy worked even when treating the eyes of very elderly mice, although it was less effective than when infecting the retina of young individuals.
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15.03.2017