Sciences de la Santé
Review: CRISPR-CAS9, Genetic Editing Technology
Yahia BELLOUCHE M. D.
Abstract The explosive development in the domains of microscopy, data analysis and molecular biology
have led us to a better understanding of cell functioning. Basic the sequence gene-protein- function might be, further mapping of the different loci and their products allowed a larger view on the pathophysiology of many illnesses, that said, almost every pathological process we could meet in the different entities, contain a quantitative and / or qualitative disorder in the sequence above. All that opened the debate on the importance of the genome and the potential benefits of the technologies of genetic editing such as the CRISPR-CAS9 system, subject of our discussion.
Basic concepts
Every Cell in the body holds a complete copy of the genome, which is a set of DNA chains, organized in different structural levels, resulting from chemical links between millions of nucleic acids. Each gene occupies a definite place called a locus that codes for at least one“ functional molecule”, proteins mostly, that induce a given change somewhere in the cell or out of intracellular compartment. The sequence explained above is not in fact simple, many processes follow up to the final effector. Copies are made of the gene in the form of mRNA after transcription, they transit into the cytosol and get translated by means of polysomes onto proteins that can submit some modification( glycosylation, cleavage, conformational maturity ….), before they get addressed to the corresponding compartment where they accomplish the tasks supposed. This model implies an“ On demand” gene expression system rather than a“ Continuous” one. The general regulation loop scheme is very much valid In this context, this means that a stimulus can induce which gene to be expressed and when, recent data suggests further control of external milieu, one that commands how and what is transcribed in a gene, which means that a phenotype is in fact, an interaction product between an intrinsic genetic code and some surrounding conditions, study subject for Epigenetics. As a result, the environment of a cell and its level of differentiation define various functional stages where a cell performs different tasks and exposes many changes. The pool of proteins expressed by a cell in a given functional state is known as a proteome, its field of study Proteomics. Same definitions can be applied to the genome, genomics respectively. Considering now the pathological side, an interactive and dynamic genome, beneficial for a cell on one
hand, would only mean extra vulnerability to modifications and alterations on the other. A fact that can be largely deduced from the genetic analysis of affected cells from many examples such as cancer, viral infections and inflammatory response. However, those are extremely rare, and even with the presence of many potential alteration inducers, the genome is somewhat sane, this has been studied largely through the last decade and many protection systems were discovered, the CRISPR-CAS9 being one of those.
CRISPR-CAS9 system in prokaryotes Experimental data from the 1980s discovered that species of E. Coli could resist a viral infection after a few generations, raising a question about the mechanisms. Bacteriophages( viruses infecting bacteria) contain some genetic sequences that – after penetration- get integrated in the bacteria genome causing alterations and modifications through transcription. These sequences code for viral structure proteins and mandatory enzymatic material. Throughout the natural history of infection, some colonies begin to expose a certain degree of resistance, documented by the deceleration of viral multiplication rates. Further analysis of the bacterial genome detected some DNA sequences originating from the virus itself. The questions about the mechanisms were not solved until 2007 with the work of Barrangou & Col, where the CRISPR-CAS system was well understood. Studies have concluded that some gene loci in the genome were the association result of pieces of repetitive sequences and some viral sequences called spacers. That said, the CRISPR loci transcription product was found to be a special type of RNA( called crRNA) that had the ability to bind a set of proteins such as CAS, the resistance to viral infection appears after two phases,
12 Hiver 2018