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CRISPR partially restores sight in blind rats

21 November 2016

By Paul Waldron

Appeared in BioNews 878

Scientists in the US have used a genome-editing technique to partially restore vision in blind rats.

This is the first time that such techniques have been used to add genetic code to the genomes of adult cells which have stopped dividing. Previously, the CRISPR/Cas9 system could only be effectively used in dividing cells, such as stem cells and some adult cells like skin and gut.

'We now have a technology that allows us to modify the DNA of non-dividing cells, to fix broken genes in the brain, heart and liver,' said Professor Juan Carlos Izpisua Belmonte of the Salk Institute, California, and lead author of the study. 'It allows us for the first time to be able to dream of curing diseases that we couldn't before, which is exciting.'

In the study, published in Nature, the researchers used a modified version of the CRISPR/Cas9 system of genome editing. After cutting the DNA in a cell and inserting replacement DNA, the genome-editing process normally relies on a DNA-repair mechanism present in all dividing cells to re-join the DNA strand ends. However, some adult cells such as those of the eye, brain, or heart do not divide so cannot use this mechanism.

The team used a different DNA-repair cellular pathway, 'non-homologous end-joining' (NHEJ) found in adult cells, and paired it with an updated way of inserting replacement DNA, called homology-independent targeted integration (HITI) – delivering this package of molecular tools to the target cells using a modified virus. The result demonstrated that new genes could be inserted into adult nerve cells in the lab, and also into the brain cells of living adult mice.

'Using this NHEJ pathway to insert entirely new DNA is revolutionary for editing the genome in live adult organisms,' said Dr Keiichiro Suzuki of the Salk Institute and one of the paper's lead authors. 'No one has done this before.'

Finally, the researchers used this technique on rats which had a genetic mutation in the Mertk gene, expressed in the eye. In these rats, cells in the light-sensitive retina at the back of the eye die and vision is lost. This is similar to the inherited human disease retinitis pigmentosa.

Rats which were treated with the HITI system to introduce the correct Mertk gene showed increased production of the healthy form of Mertk protein in some cells, and an increase in their visual function. The researchers wrote however that 'the rescue was only partial and not enough to completely restore vision'.

Dr Andrew Wood of the University of Edinburgh, who was not involved in the work, said: 'This study is a really exciting development for therapeutic applications of genome editing. Before it can be applied to humans, it is now important to improve the efficiency with which the genome-editing molecules can be delivered to the relevant cells.'

On Wednesday 7 December 2017, genome editing and embryo research will be debated at the Progress Educational Trust's public conference 'Rethinking the Ethics of Embryo Research: Genome Editing, 14 Days and Beyond'.

Click here for full for full details, including the conference agenda and how to book your tickets, and email with any queries.

RELATED ARTICLES FROM THE BIONEWS ARCHIVE

26 June 2017 - by Meghna Kataria 
Eliminating the faulty protein that causes Huntingdon's disease goes some way to reversing disease progression in mice, a study has found...
08 May 2017 - by Emma Laycock 
US scientists have used CRISPR gene-editing to remove HIV DNA from the genomes of living animals, eliminating further infection.
09 January 2017 - by Dr Özge Özkaya 
Scientists have discovered a new set of proteins that can block the CRISPR/Cas9 system...

03 May 2016 - by Sarah Gregory 
A trial of gene therapy for choroideremia, a rare form of inherited blindness, has partially restored the vision of several patients...
01 February 2016 - by Kulraj Singh Bhangra 
Researchers have used the CRISPR/Cas9 genome-editing technique to correct a genetic mutation that causes blindness...
16 November 2015 - by Ari Haque 
A US biotechnology start-up co-founded by two pioneers of CRISPR technology intends to begin gene editing in humans as part of an experimental treatment to target a rare genetic eye disorder...
15 December 2014 - by Dr Rosie Gilchrist 
Scientists have used gene therapy to restore some sight to animals with visual impairment similar to retinosa pigmentosa, a type of human blindness...
16 January 2014 - by Siobhan Chan 
Gene therapy for an eye condition called choroideremia is safe and has improved the vision of six patients, says a study in the Lancet...

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