Nucleic acid sequencing: methods, applications, developments and challenges

DNA, or deoxyribonucleic acid, is the genetic information carrier of all living organisms, forming a double-stranded helix. Each strand is made up of a sequence of nucleotides, themselves consisting of a sugar, a phosphate group and a nitrogenous base: adenine, cytosine, guanine or thymine. These are the main elements of an organism's genetic code.

This sequence of nucleotides forms the genes which, within each cell, code for the information necessary for the development, maintenance and reproduction of an organism. The size of a genome (a cell's entire genetic material containing all coding and non-coding sequences) can vary from a few thousand bases for viruses, to a few million for bacteria (4.6 megabases or Mb for Escherichia coli) and a few billion for multi-cellular organisms (3.4 gigabases or Gb for humans).

Sequencing is the reading of the succession of nucleotides along a DNA molecule. The result is a text written in the alphabet A, C, G, T. Sequencers read fragments of several bases, called "reads", whose length varies according to the technology. The genome of an organism is then obtained by assembling the reads. Since the mid-2000s, high-throughput sequencers have become an indispensable tool for biological research, particularly in the medical field.

Deciphering genomes is a major challenge for scientific research. It helps us to better understand how living beings function, and has numerous applications in every field of expertise: medicine, the environment, agriculture, etc.

Demand has never been greater for revolutionary technologies that provide fast, accurate and inexpensive information about the genome. Technical advances in recent years have made sequencing faster and more efficient. Since the 1970s, with the advent of enzymatic sequencing using the Sanger method, a number of technical hurdles have been overcome, leading to high-throughput sequencing. In this article, we present these developments, which have led to a considerable increase in data volume, a reduction in the time required to perform sequencing, and a reduction in the cost of sequencing. We will also discuss the wide range of applications for sequencing technologies, and provide guidelines for selecting platforms to answer biological questions of interest.

Finally, we'll discuss the consequences of such a revolution. Tomorrow, thanks to genome decryption, it may be possible to make a personalized diagnosis of each individual, and thus put in place appropriate, ultra-personalized treatments. Is knowing what diseases we'll be suffering from in the future a blessing or a burden?