Yeast, a cellular model

Man is a eukaryotic organism. This means that the genetic material of human cells is present in a delimited nucleus and in the mitochondria (specialised organites). Like humans, yeast is a eukaryotic organism, as opposed to procaryotic organisms such as bacteria.

But contrary to humans, made up of billions of cells, yeast is unicellular! That is why it is easier to study and handle.
 

Saccharomyces cerevisiae yeast is a complex and particularly efficient living organism and almost half of its genes are similar to those found in mammals. It is one of the top-ranking biological models, close to the human cell in terms of organisation and metabolism (chemical reactions needed to live and for cells to multiply). That is why, for this and other reasons, we owe much of our knowledge on the cellular operation of eukaryotes - human, animal and plant - to yeast. Other yeasts such as Schizosaccharomyces pombe are also used as eukaryotic models in fundamental research.

Yeast is a model as it is easy and economical to handle: it is unicellular, reproduces fast (duplication in barely two hours in most cases) and is remarkably adapted to genetic analysis. Moreover it is the first eukaryotic micro-organism whose genome has been entirely characterised: the sequence of its sixteen chromosomes is fully known.

Hundreds of human genes are capable of replacing their counterpart in yeast, which makes it easier to study their role. But in the past ten years, two Nobel prizes - in Physiology and Medicine - have been awarded to researchers having used yeast in their work to understand fundamental aspects of how human cells function.

The first, in 2001, rewarded the discovery of the different stages of the cell cycle and its control mechanisms (in particular genetic). The importance of such information is considerable in view of the fact that tens of thousands of billions of human cells come from one original cell... Work on yeast also helped to decode the role played by certain human genes without having to study them directly in humans!

The second Nobel Prize, in 2009, highlighted the importance of the role of telomers - which protect chromosomes from deterioration - through studies on yeast. The results were extrapolated to understand ageing (during which telomers are seen to shorten in time) and cancer (telomer synthesis is frequently more active in cancerous cells).

Its cellular model status gives yeast possibilities broadly exploited by man.  Hundreds of genes responsible for orphan diseases have thus already been identified - such as cystic fibrosis and Leigh syndrome.

The mechanisms of certain diseases such as Alzheimer, late onset diabetes or migraine have also been studied.

By using human genes in yeasts, it is possible to test the efficiency of new drugs or the effect of various substances, without having to use human or animal guinea pigs. Finally, scientific breakthroughs made in yeast have allowed the technical development of new and valuable methods and tools in research.

But we do not yet know everything about yeast! The functions of about a quarter of its genes are not yet known and many mechanisms remain to be decoded, in particular certain aspects concerning the organisation of its genome, its interaction with the environment or its evolution. The international scientific community of "yeast specialists" is dynamically focusing on these questions.

However, knowledge already acquired and the intrinsic quality of yeast, such as resistance to difficult environments or its relatively simple nutritive needs, make Saccharomyces cerevisiae a choice model on which to elaborate new molecule creation strategies aimed at nutrition, human or animal health and energy and to develop new methods and tools indispensable to the "cell factory" concept.