At ULB, Thomas attended lectures by Jean Brachet, who pioneered the field of nucleic acids (DNA and RNA) and their role in heredity and protein synthesis.
[1] After two years of postdoctoral training in the laboratories of Harriet Ephrussi (Paris, France, 1953–1954) and of Alfred Hershey (Cold Spring Harbour, USA, 1957–1958), Thomas returned to ULB in 1958, where he was appointed to lecture on Genetics.
Thomas' career was attested by a number of prestigious awards, including the Francqui prize in 1975, the five-year prize of the Belgian National Funds for Scientific Research (FNRS) in 1985 for his discoveries on DNA, genetic transformation of bacteria and bacteriophages and the Grande Médaille from the French Academy of Sciences in 1999.
Thomas discovered that the UV absorption of native DNA is far lower than expected from a "theoretical" spectrum built from the extinction coefficients of its component nucleotides.
[9] The existence of positive regulation and that of regulatory cascades were later found to play essential roles in the development of all multicellular organisms, including humans.
The intricacies of the regulatory network controlling the decision between lysis and lysogeny by bacteriophage lambda led Thomas to realise that understanding phage behaviour based on the sole intuition became very difficult.
Thomas learned how to use the Boolean formalism by attending classes of his colleague Jean Florine at the Université Libre de Bruxelles.
On the one hand, positive circuits, involving an even number of negative interactions (or none) can lead to the coexistence of multiple dynamical regimes.
[17] This has major biological implications since, as first pointed out by Max Delbrück[18] and amply confirmed since, cell differentiation essentially results from successive choices between multiple steady states.
Two articles by Thomas and Marcelline Kaufman compare the logical and differential predictions of the number and nature of the steady states.
[29][30] Indeed, regulatory circuits can be defined formally as sets of non-empty elements of the Jacobian matrix (or of the interaction graph) of dynamical systems such that the line and column indices are in circular permutation.
With this in mind, a number of surprisingly simple sets of first order differential equations were constructed and shown to display deterministic chaos.
While he was inflexible about scientific rigor, he readily provided his students with a vast freedom of thoughts, experimental design and publication.
Many of them, including Martine Thilly, Suzanne Mousset, Albert Herzog, Alex Bollen, Christine Dambly, Josiane Szpirer, Ariane Toussaint, Jean-Pierre Lecocq, Jean Richelle and Denis Thieffry went on pursuing scientific careers in Belgium and France, in the field of molecular genetics on a large set of organisms, from phages to bacteria, fungi, drosophila, zebra fish and humans.
As Thomas shifted his research interest from biochemistry to phage genetics, then to mathematical biology and finally to dynamical systems, he addressed complex theoretical questions with an experimental mind frame, moving from wet experiments to computational simulations.
A series of testimonies and tribute articles can be found in a special issue of the Journal of Theoretical Biology dedicated to the memory of René Thomas and published in 2019.