By Santanu Chakraborty
The problem extends beyond that of accuracy of snipping out bits of DNA and replacing them with other sequences
Editing of human genomes is commonplace in laboratories around the world. What I mean by that is scientists routinely tinker with the genomes of individual cells derived from humans and being grown in a dish. More generally, various mammals typically mice are used as model systems to develop genetic technologies of the future. It is in these systems small animals and cells growing in dishes that the technologies of the future are first developed. The aim is two fold, one is to understand the mechanisms of life well and the other is to use them for human benefit. So it is hardly a surprise that the editing of entire human genomes would happen sooner or later, even if it should violate ethical norms of the day. One such work was revealed recently when scientists in China led by He Jiankui used a newly developed gene editing tool, commonly known as CRISPR, to create babies meant to be resistant to the HIV virus. This proved extremely controversial setting off a debate, to put it politely, that continues to rage.
There is a de-facto embargo on editing the genomes on embryos. Why should that be a problem and editing single cells in the laboratory not? To understand that and put some more recent work, which I will refer to later, into context let us consider the following. How would you go about curing a genetic disease if you had the ability to alter the genome of a single cell? Note that the genome of a human cell is contained in a few massive threadlike molecules made up of only four component molecules whose combined length when strung together is approximately four billion molecules long. This exists inside the nucleus, a balloon like compartment inside the cell. Now all this happens on a tiny scale as each cell is only a few microns in diameter with one micron being only a millionth of a meter. Life has evolved molecular machines to work at this scale selecting its components and ways of putting them together over millions of years.
Experiments of mice have yielded extremely powerful proofs of concept which continues to drive the development of such technologies. A recent paper by Peter et al. (Nature Communications, 2019, 10:4112) used CRISPR to alter the genome of mice to recover lost neuronal connectivity. A certain gene (something called C11orf46 but we will call it Gene 1 for short) is implicated in the loss of neuronal fibers that connect one half of the brain to the other.
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Another way to edit the genome - Bangalore Mirror
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