CRISPR is an extremely useful tool for mouse models but is not ready for use on human embryos

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By IMPC

Published 28th November 2018

A researcher in China claims to have produced the first genome-edited babies through using CRISPR. The IMPC uses the CRISPR/Cas9 system to generate the required knockout mouse lines. The project moved to use this technology because of its speed and accuracy, yet those involved in controlling and implementing CRISPR are keen to stress there is a long way to go before this technology should be implemented in human embryos. A recent blog post and video highlight how and why the IMPC uses this technique: Two new articles highlight the usefulness and intricacies of CRISPR/Cas9 technology & CRISPR-Cas9 and mouse genomics

Dr Lydia Teboul, Head of Molecular and Cellular Biology at the Mary Lyon Centre at MRC Harwell said “We have been using the CRISPR/Cas9 system over the past four years to create over 200 mouse lines with new mutations as part of our work for the International Mouse Phenotyping Consortium. We have learned a lot about the technology in the process. A key feature of these genome editing tools is the unpredictability of the outcome of applying them to embryos. Because of this, it is clear that the technology is not ready for use for assisted reproduction in clinic.”

Vchal/Shutterstock

The below article is republished under a Creative Commons license and highlights some of the main issues with altering human embryo DNA.


By Joyce Harper, UCL

A scientist in China claims to have produced the world’s first genome-edited babies by altering their DNA to increase their resistance to HIV. Aside from the lack of verifiable evidence for this non peer-reviewed claim, this research is premature, dangerous and irresponsible.

He Jiankui from the Southern University of Science and Technology in Shenzhen (which has reportedly since suspended him) said he edited the DNA of seven embryos being used for fertility treatment, so far resulting in the birth of one set of twin girls. He says he used the tool known as CRISPR to delete the embryos’ CCR5 gene (C-C motif chemokine receptor 5), mutations in which are linked to resistance to HIV infection.

If true, this is a significant advance in genetic science, but there are some very serious problems with this news. First, the research has not yet been published in a peer-reviewed journal so we cannot be sure of the exact details of what has been done. Instead, the scientist made the claims to the Associated Press news organisation, and the journalists involved haven’t been able to independently verify them. The parents of the allegedly gene-edited babies declined to be interviewed or identified.

Second, we know there can be significant problems with using existing gene-editing technology on human embryos. The main two issues are mosaicism, where the edited DNA does not appear in every cell of the embryo, and off-target effects, where other parts of the genome may also have been edited with unknown consequences.

Before genome editing becomes a clinical treatment, it is essential that scientists resolve both of these issues and eliminate other potential adverse effects on the embryo. We need comprehensive studies to show that genome editing is not going to cause harm to the future people it helps create. Any children born as a result of genome editing will also need long-term follow up. It would be vital to see the preliminary work that He has done to confirm that his technique has eliminated mosaicism and off-target effects, and it is surprising that he has not published this.

 

There is also a question over why gene-editing was used to tackle the particular issue of HIV transmission in this case. The reports suggest that the couples involved in the study were made up of HIV-positive men who had the infection under control and HIV-negative women. The risk of transmission of HIV for these couples would have been negligible, and there are well-established ways to prevent HIV transmission to the offspring of HIV-positive couples.

Finally, there is the wider ethical debate, which the scientist in this case has chosen to ignore. I was a member of the Nuffield Council on Bioethics working group. We spent 20 months examining all aspects of genome editing and published our report this summer. Our conclusion was that we needed a public debate before gene editing on embryos was carried out because this procedure takes reproduction to a new level.

Do we really need gene editing?

Most reports suggest that the potential main use of genome editing would be therapeutic genome editing to prevent the transmission of genetic diseases, such as cystic fibrosis. In most cases, couples at risk of transmitting a genetic disease to their children are able to prevent transmission using established techniques of screening before birth or even before an embryo is implanted via IVF. So perhaps editing embryos for therapeutic reasons is not the way forward.

But genome editing could also more controversially used for genetic enhancements, such as ensuring children have a particular desirable characteristic such as a certain eye colour. This raises even more ethical questions.

We also need legislation. In the UK, for example, the use of genome editing would be regulated by the Human Fertilisation and Embryology Authority, and would currently be illegal. Before this technique becomes a treatment, governments need to pass laws that will control and regulate it otherwise it could easily be misused.

With all this in mind, any research in this area needs to be peer-reviewed and published in the scientific literature, with all the necessary preliminary work, so that we can make a valued analysis of the technique. In bypassing this process, He has made our job much harder.The Conversation

Joyce Harper, Professor of Reproductive Science, UCL

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The entire genome of many species has now been sequenced, but the function of the majority of genes still remains unknown. This is where the International Mouse Phenotyping Consortium (IMPC) comes in, with the goal of characterising all 20,000 or so protein-coding mouse genes. To achieve this, genes are systematically inactivated then mice are put through a standardised phenotyping platform, with tests undertaken across a broad range of biological systems.

The consortium is comprised of 19 research institutions, 5 national funders and 11 countries. Each centre focuses on particular genes, applies standardised tests and then records the resulting data. After this, phenotype analysis is conducted and the resulting data and statistics made freely available to the research community. As well as completing large scale comparative studies, the overall aim of the project is to create a platform for this data where researchers and clinicians can search for genes, phenotypes or diseases of interest to help them understand human biology, health and disease.

Professor Steve Brown, the IMPC chair says “The IMPC is rising to the challenge of generating a complete functional catalogue of the mouse genome. Since its inception in 2011, it has made great strides with a third of the genome already analysed. Moreover, many startling and hitherto undiscovered features of the mammalian genome landscape have been revealed.”

There are now over 6,000 genes with mouse mutant data on an isogenic genetic background (C57BL/6N) on the IMPC website, all of which can be viewed and downloaded for free. In its initial stages the knock out lines used for IMPC were all made in ES cells by homologous recombination, all containing a lacZ reporter and many of them generating conditional mouse lines. However, as for many areas of developmental biology, new gene editing technologies, in particular CRISPR/Cas9, have condensed the process of generating knockout mouse lines. Advancements such as this have improved production and will allow all 20,000 genes to be characterised in the next few years.

Around a third of knockout genes are embryonic lethal and consequently developmental biology is an integral part of the IMPC project. In particular, there is an extensive embryo phenotyping pipeline that includes systematic harvest of embryos at set stages, capture of morphology by 3D imaging (OPT or microCT, depending on embryonic stages) and evaluations of morphological abnormalities in mutant embryos. These procedures can allow direct insight into the window of lethality for each mouse line, but they also provide valuable information on gene function. For example, accurate measurements of organ size and shape can be collected using microCT scan data, or macroscopic observations undertaken by a trained researcher. Importantly, all 3D data sets are available to download from the website for further in-depth analysis by specialist researchers.

In the last few years the IMPC has made major discoveries about parts of the genome that were up to now unexplored, with novel genes discovered relating to areas such as embryonic development, deafness, diabetes, and rare diseases. Recent high profile publications have included research focusing on inferring mammalian gene function, studies on specific human conditions, sexual dimorphism in mouse research, and even using IMPC data to help in wildlife conservation. New methods and analysis tools have also been developed under the umbrella of the IMPC, such as PhenStat, an extensive library of functions that analyse the phenotypical data. Another example is illustrated by a recent article that highlights a new bioimage informatics platform for high-throughput embryo phenotyping. Although this platform was built for the IMPC, the software tools that facilitate the analysis and dissemination of 3D images can be used by other researchers, and is available under an open-source licence. Indeed, sharing resources across the research community is a crucial aspect of the IMPC, and mutant mouse lines can be obtained from the website.

The IMPC is continuing to deliver data and mouse models for the developmental biology field and ultimately will be part of the effort to understanding and treating genetic conditions in humans. More information on the latest research of the IMPC can be found on our blog, and you can search the IMPC database for free at https://www.mousephenotype.org/.

Get in touch with us at info@mousephenotype.org

The International Mouse Phenotyping Consortium (IMPC) has been predominantly interested in using mouse models to understand human health and disease. In a new study in the journal Conservation Genetics researchers have found another intriguing use of IMPC data.

By comparing genetic functional data from the IMPC with other non-human animals, it may be possible to identify genes relevant for the normal development in those species. For example, by comparing mouse genetic functional data with genomic data for selected species with specific diseases, improved breeding management could be implemented.

To test this potential application researchers at the European Bioinformatics Institute (EMBL-EBI) and Queen Mary University London (QMUL), alongside colleagues from the IMPC, compared genetic functional data from mice with genomic data from gorillas, showing how such analyses could aid in the identification of genes essential for healthy development.

As well as gorillas, the researchers highlighted other examples, including cheetahs, polar bears, wolves, pandas and cattle. This type of analysis could improve the current management approaches to breeding endangered species, by allowing researchers to identify the matches that are most likely to produce healthy offspring or select breeders to preserve genetic variation relevant for adaptation.

Genes associated with fat metabolism can be a real asset for species like polar bears

Heart disease is a common cause of death for gorillas in captivity and cheetahs suffer from impaired fertility both in captivity and in the wild. By identifying gorilla genes linked to heart disease or cheetah genes linked to infertility, researchers could help better understand the cause for the condition, which is the first step to envisage ways to prevent it. Similarly, this type of data could help identify genes linked to adaptation in certain mammals. For example, genes associated with fat metabolism can be a real asset for species like polar bears, which have diets rich in fats in the extreme environment of the Arctic.

Impaired fertility is common in cheetahs both in captivity and in the wild

“When the number of individuals of a species dramatically decreases, loss of genetic variation also takes place”, explains Violeta Muñoz-Fuentes, Biologist at EMBL-EBI. “This can result in many offspring not surviving, or exhibiting genetic defects linked to fertility or health problems.”

“Many zoos and wildlife conservation centres are seeing excellent results through their breeding programmes. Currently, many focus on minimising inbreeding. By adding a functional genetic dimension to the selective process, conservation geneticists can identify the crosses that would, for example, avoid a gene variant linked to disease in the offspring. It is nevertheless important to keep in mind that for a genetic rescue approach to be successful in the long term, the conditions that led to the decrease of individuals need to be removed; otherwise, the accumulation of deleterious alleles will likely take place again”.

Number of IMPC significant phenotypes for selected mammalian species (source: http://bit.ly/conservationarticle)

Although this type of research is still in its early stages, gene functional knowledge is a powerful tool for maximising adaptive genetic diversity within a species and even for reducing genetic variants that negatively affect an individuals’ health and survival. With the accumulation of gene function annotation by the IMPC, as well as technical advancements in gene editing such as CRISPR/Cas9, the hope is that this method of comparing genome information between laboratory mice and endangered wildlife will help in future conservation projects.

The IMPC aims to produce and phenotype knockout mouse lines for 20,000 genes

The IMPC would like to encourage conservation geneticists, conservation centres and zoos to get in touch if they are interested in using IMPC data for conservation purposes.

Jesse Mager discusses his work in mammalian developmental genetics, and how he uses IMPC data for this research.

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By IMPC

Published 5th April 2018

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