Whispers about CRISPR

Note: This is Part 1 of a 2-part article about CRISPR, which will be concluded next week.

The explosive growth of scientific discovery over the last century or so shows no sign of slowing. From the grand, majestic vistas of modern astronomy to much humbler findings in a multitude of areas, there always seems to be something new. One of these humble findings – so humble that hardly anyone took any notice of it for the next 26 years – was the discovery of the principles of genetics by an obscure monk named Gregor Mendel, beginning in the year 1874.

This is hardly surprising, considering that Mendel’s tasks were incredibly boring: pollinating and growing pea plants, counting the peas – no one knows how many, but probably in the hundreds of thousands – and analysing the results. It was only in 1900, 16 years after Mendel’s death, that several other scientists rediscovered his findings and understood their significance.

And yet Mendel’s staggering legacy is the myriad of directions genetics has taken since then and the fact that the pace of development has not shown any sign of slowing in over a century.

Fast forward to the present.

Probably the most exciting recent development in genetics has been CRISPR, the gene editing software discovered in the 1980s. The name is an acronym for its structure, which consists of bits of bacterial DNA Clustered Regularly and Interspaced with other Short bits of DNA in the form of Palindromic Repeats.[1]

Between the years 2007 and 2010 several groups carried out experiments demonstrating that CRISPR is an immune system used to protect bacteria against viruses.[2]

A very clever team of scientists, led by Jennifer Doudna (UK) and Emmanuelle Charpentier (France), worked out a way to make a simplified, artificial version of this system, called CRISPR/Cas9, which can be used to edit the genomes of more complex organisms, such as plants, animals and humans.

Doudna Charpentier

Jennifer Doudna (left) and Emmanuelle Charpentier

The two main parts of the CRISPR/Cas9 system are an enzyme (Cas9) which cuts a DNA molecule at a particular precise point, and an RNA molecule which guides the enzyme to the point where the cut is to be made.

The most valuable part is that this system can be made to cut any piece of DNA, simply by altering the RNA, because RNA bonds precisely with its complementary DNA molecule. This is much easier than any other gene editing system discovered so far.

And that is both the exciting and the terrifying aspect of the system. In other words, the prospects are boundless, but so are the risks.

Of course, the whole system is vastly more complex than I have described it here. Anyone wishing to learn more about the system should go to the great variety of online resources, including the Wikipedia article, which to my mind seems amazingly comprehensive.

CRISPR has enormous potential for good, because it can be used to repair many types of mutations causing genetic diseases far more quickly and accurately than any other technology previously known.

[1] A palindrome is a sequence of characters (e.g. letters, numbers) that reads exactly the same backwards or forwards. Simple palindromes include names such as Anna and Bob. Who could forget such famous palindromes as “Madam I’m Adam” (the first man’s introduction to his wife) and “Able was I ere I saw Elba,” (attributed to Napoleon)?

[2] Spare a thought for the poor bacteria which would be dead in minutes if not for CRISPR and related systems which allow them to defend themselves against viruses. (And please don’t forget that the overwhelming majority of bacteria are friendly chaps that just want to get on with the rest of us; the nasty pathogenic types are, relatively speaking, very rare.)

 

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