Published on 3 July 2015

Raphaël Mercier Interview
Research Director at INRA
Institut Jean-Pierre Bourgin

Mitosis and Meiosis, two fundamental divisions that bring us together

There are 2 types of cell divisions in the living world: mitosis and meiosis.
Mitosis is most often described: it consists in dividing a cell into two other identical cells. It is usually said that it is the division of a "mother" cell into two "girls" cells even if it's actually asexual division. Mitosis takes place throughout life, from fertilization to death, every time a cell needs to renew itself. It ensures that the genetic heritage of an individual is the same in all cells.
Meiosis is cell division that allows to create gametes (sperm / grain of pollen and ovules) and ensures the lifecycle of sexually reproducing organisms.
For humans being it occurs at the stage of the embryo and helps to form the stock of oocytes, for women. For men meiosis occurs continuously from puberty in the testicles and ensures the production of sperm.
It is this process which ensures the genetic diversity because the creation of gametes assumes recombination of chromosomes, each containing thousands of genes. This is what allows that brothers and sisters have a different genetic makeup despite the fact that they have the same parents, for instance.
This is the same process in all eukaryotic organisms, that is to say, whose cells have a nucleus: animals, plants, mushrooms...

The recombination of chromosomes: a game of chance with complex rules

Each Meiosis are different and produce 4 new cells, from the principal cell, that become gametes containing only one copy of each chromosome, unlike other cells that contain a pair of chromosomes. In addition, this copy of each chromosome is not one of the two present in the parent, but a mixture of the two chromosomes of the parent. During meiosis the chromosomes of one pair break and exchange their DNA and their genes, it is called the "crossing-over".
Consequently each gamete is unique, having inherited a random selection of the parent’s genes. During fertilization, two gametes merged producing child's first cell that will possess two copies of each chromosome, each copy being unique, one coming from the meiotic lottery of the mother, the other coming from the meiotic lottery of the father.

This recombination is the base of the individuals’ characteristics and that what make their uniqueness and diversity.

10,000 years of plant breeding
The process of meiosis was discovered in the early 20th century and the development of experimental techniques in biology and genetics allowed to have a better understanding of this division-recombination essential to the reproduction and growth of species.

But Human has started to select species several millennia ago, particularly to develop varieties of food. We will not be able to eat tomatoes, corn, bread or drink coffee if we were in need to eat only wild plants.

Therefore, we know how is made recombination, we can measure the effects but we do not yet know, for instance,  why meiosis is sometimes defective or why "crossing over" occur in some segments of chromosomes and not other.
The purpose of these questions and the research conducted is essentially important but can also facilitate the work of agronomists in the creation of varieties.

Understand the molecular working system to understand the evolution of species
Research on meiosis can serve three purposes:
- Understand the evolution of species and how they adapt (for instance: to climate change

- Facilitate the development of new plants by selection or combination of genes
- Accompany some medical research related to meiosis defect
Raphaël Mercier and his team develop experimental protocols in order to serve these three objectives. Many questions remain: what are the molecular mechanisms that determine the number and the position of crossing-over, and especially concerning that hundreds of DNA breaks during meiosis, just few recombinations occur? ; What are the mechanisms that ensure the right number of chromosomes in the gametes? Can we induce reproduction without meiosis?

Their research is conducted on Arabidopsis and has emerged as one of the leading models in the field of the study of meiosis. They have shown that meiosis can be modifed into mitosis (Erfurt et al, PLoS Biol 2009; Marimuthu et al Science 2011) and identified factors that limit meiotic recombination (Crismani et al, Science, 2012, Seguela et al PNAS 2015, Girard et al PLoS Genetics 2015). "

A wide scientific community

Researchers interested in these recombination processes are extremely numerous and constitute the "scientific community of meiosis."
They meet once a year to discuss their work. The next meeting held at Oxford, September 2015 (More info)
By then Raphaël Mercier will introduce his work to the plant biology’s scientific interest group  and at ICAR 2015, where his intervention will be structured around 3 different mechanisms involving multiple genes which are responsible for the crossing-over limitation.

To learn more on meiose, click  >here<