In the most recent issue of the Proceedings of the National Academy of Sciences USA, professor Carsten Peterson and his collaborators Bjrn Samuelsson and Carl Troein demonstrate how this is possible. The American physician and scientist Stuart Kauffman a pioneer in the field, who formulated and attempted to solve the problem as early as 1967 is their co-author.
At any given time, each of the 25,000 genes in a cell may or may not be producing a protein each gene is 'on' or 'off', to use language from the world of computers. A gene can affect other genes, turning them 'on' or 'off'. A simple case is that two genes are controlling a third gene. To activate this third gene, both the controlling genes might need to be active, or maybe only one or the other.
"In such a simple subsystem, sixteen different rules are possible in the interaction between the genes, and a large number of different solutions can emerge for the entire network," says professor Peterson. It was systems like this that Dr. Kauffman started working with; he assumed that the different solutions corresponded to different cell types. This would also explain how the DNA can be the same in all types of cells. Unfortunately, real systems are vastly more complicated. More than two genes may be involved in activating a single gene.
Contact: Gran Frankel
Swedish Research Council