One of the most impressive developments in molecular biology is the
ability to change the DNA of living organisms. Techniques for real-time
genetic modification are complex and diverse; often involving a large
protein capable of binding to a specific sequence of DNA and cutting it at
that sequence. Zinc finger nucleases (ZLN’s) and transcription
activator-like effector nucleases (TALEN’s) are examples of such protein
complexes. However, these techniques remain time consuming and
costly for the examination and alteration of large genomes.
And while the genomes of prokaryotic organisms like bacteria are
relatively simple, those of eukaryotic organisms like plants and mammals
are quite complicated and difficult to modify. Fortunately, researchers in
Harvard professor George Church’s laboratory are developing a
technique called CRISPR (clustered regularly interspaced short
palindromic repeats) for altering the DNA of human cells. CRISPR, like
most techniques in molecular biology, is derived from a natural process
in bacteria and archaea as an immune response to invading viruses.
In CRISPR, a small 20 nucleotide strand of RNA (sgRNA) binds to a
DNA region of interest. This sgRNA is bound to a protein (Cas9) which
breaks the DNA strand, allowing for an additional DNA segment to be
inserted between the break. CRISPR has also been used as a means to
regulate the activity of DNA which is already present in an organism’s
genome, either by increasing or decreasing protein expression.
The biological impact of scientists and doctors developing a means for
editing human DNA is enormous. An individual with a disease could
have their genome sequenced to determine their genetic defect;
scientists could create a complement RNA molecule to bind to this
mutated DNA region, cut, and replace it with a fully functioning DNA
Synthetic biologists could also use this technique to add completely
unique gene segments to human beings. From a moral standpoint,
improvement of the human being can be a controversial topic – critics
claim that we do not have the right to ‘play God’, but I think we would all
agree; if CRISPR can give me wings or the ability to produce my own
milk, I will forget about any ethical dilemma.
Frøkjær-Jensen, C. (2013). Exciting prospects for precise engineering of caenorhabditis elegans genomes
with CRISPR/Cas9. GeneticsGeneticsGenetics, 195, 635-642.
Lim, W., et al. (2013) Resource CRISPR-mediated modular RNA-guided regulation of transcription in