From 2007.igem.org

How can we define a multicellular organism ?

There is no universally admitted definition. Wikipedia gives: "an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function in some way as a stable whole."

For us, the organs will simply be different cells. The definition we retain is that of a multicellular entity with different types of cells fulfilling different complementary tasks.

In most organisms, some cells differentiate to realize a function useful for the organism. By useful, we mean that it will give a better fitness, or in other terms, that it will help producing more offspring. The specialized cells are usually not the same than the ones reproducing the organism, and they loose this ability. Thus, their is a notion of sacrifice of some cells to the profit of those dedicated to reproduction. The cells are able to reproduce the organism represent the germline, the ones which specialize and loose this ability represent the soma.

How to proceed ?

The question is: how can we make a cell differentiate into two distinguished lines? According to us, the answer is the Cre/loxP system. We will introduce a special genetic construction into the bacterial chromosome; the excision of a cassette framed by loxP sites will lead to the differentiation of these cells into soma. In other words, the original germ cell gives a soma cell when a particular cassette is excised consequently to Cre/LoxP-system action. The construction could be simply represented in that way: