Oligonucleotide

Una variedad de grupos étnicos viven en Gambia, cada uno de los cuales conserva su propio idioma y tradiciones. La etnia Mandinka es la más numerosa, seguida de los Fula, Wolof, Jola/Karoninka, Serahule/Jahanka, Serers, Manjago, Bambara, Aku Marabou, Bainunka y otros, como Tukulor. El pueblo Krio, conocido localmente como Akus, constituye una de las minorías étnicas más pequeñas de Gambia. Descienden del pueblo criollo de Sierra Leona y tradicionalmente se han concentrado en la capital.

Los aproximadamente 3500 residentes no africanos incluyen europeos y familias de origen libanés (0,23 % de la población total). La mayoría de la minoría europea es británica, aunque muchos de los británicos se fueron después de la independencia.

Idiomas

Un oligonucleótido es una molécula compleja formada a su vez por varios nucleótidos, cada uno de los cuales está compuesto por una base nitrogenada, un hidrato de carbono y un grupo fosfato. La síntesis de oligonucleótidos se basa en una serie de reacciones en las que se van protegiendo y desprotegiendo cíclicamente los diferentes centros reactivos de la molécula:

• Hydroxyl 2' protector: Tert-butyl dimetilsilil (TBDMS).
• Free phosphate protector: B-cianoethyl.
• Protector of the heterocycles of the bases: different groups loved.

Applications in gene therapy

Oligonucleotides are used in gene therapy as a strategy for gene silencing. Oligonucleotides of 12 to 20 base pairs complementary to the messenger RNA of the genes that we want to silence are used.

Inside the cell, the oligonucleotide binds to its target mRNA and blocks its translation, that is, the ribosome will translate the mRNA until the oligonucleotide is found and the process stops. Furthermore, the fact that RNaseH recognizes the oligo-RNA hybrid and degrades it is another advantage of this technique. It is important to design the oligonucleotide close to the translation start or to ensure that the possible resulting product has no biological function, for silencing to be effective.

Process of degradation of a RNA specific by ARNasa H after the formation of a RNA duplex

The ideal oligonucleotides for gene therapy should have the following characteristics:

• They must form stable complexes with genetic material.
• They must be specific to the target.
• They must possess high stability and a longer average life than usual to resist nucleases.
• They must be able to pass through the cell membranes without problems.
• They should not accumulate in cell organs or cells.
• Its size should be between 18 and 20 base pairs.

Oligonucleotides can be used in vivo, but they have a very short half-life and low concentration. Precisely because they do not have long-lasting effects, the main problem with oligonucleotides as gene therapy is that they require successive doses.

They are chemically modified to have a longer half-life, either in the oxygen of the phosphate bridges, in the bases, or in the phosphate that is not found in the bonding bridges. They are therefore considered as a drug/medication, since they do not alter DNA and end up degrading.

Potential applications of oligonucleotides could be in antiviral therapy, antibacterial therapy, antiparasitic therapy, ex vivo anticancer therapy, treatment of skin diseases, inhibition of inflammation, suppression of oncogenes or suppression of dominant genes.

Oligonucleotides for exon skipping

In mutations that cause early translational termination, oligonucleotides would be used to induce alternative splicing in the mutant mRNA, excluding the exon containing the mutation. In this way, the premature stop codon would not be read by the ribosome and the protein could continue to be translated, so the final product would be the same as the normal gene, without mutation.

Catalytic Oligonucleotides

If an Fe-EDTA molecule binds to the oligonucleotide, this causes active destruction of the bound mRNA, so the oligonucleotide can be released to degrade another mRNA.

Triple helix

An oligonucleotide could also bind to the double strand of DNA, giving rise to a structure known as a triple helix. If it binds to a specific gene, it would be inhibiting its transcription, and therefore, once again, silencing it. Only two oligonucleotides per cell (one for each chromosome in the pair) would be needed, thus avoiding the dosage problem. This technique would be useful for dominant mutations. However, the supercoiling of DNA and its interaction with histones make it difficult for the oligonucleotide to enter the double strand.

Oligonucleotide primers

These single-stranded oligonucleotides (also called 'primers') have a fundamental role for all PCR-based molecular techniques, since these oligonucleotides bind by complementarity to a DNA sequence, allowing DNA polymerase can begin the process of replication of genetic material.

Nucleotide primers are artificially synthesized with the goal of binding specifically to a known DNA sequence. However, they must meet a series of requirements (length, guanine and cytosine content, absence of complementary areas between them or in the oligonucleotide itself...) necessary for them to carry out their function.