What history tells us XVI. A third pillar for molecular biology: Molecular embryology

Abstract

It is generally acknowledged that the rise of molecular biology was a result of the encounter of two different research traditions: the structural chemistry and biochemistry tradition, with the progressive description of macromolecular structures, and the informational vision rooted in genetics (Morange 1998). The development of molecular biology, however, is more complex than this convergence suggests, and other disciplines such as microbiology, cell biology and embryology took an active part in the development of its concepts and of its experimental systems. Observations made in embryology supported the rise of the new molecular vision. The embryological approach of Boris Ephrussi and George Beadle – transplantation of imaginal disks in Drosophila – was at the origin of the one gene–one enzyme relation. Observations made on the variations in nucleic acid and protein turnover during development by Thomas Caspersson, Jean Brachet, Alfred Mirsky and many other embryologists helped to position the different macromolecules on the chart of informational transfer which was substituted for the genotype–phenotype relation. I would like to argue that molecular embryology was more than a simple contributor to the development of the molecular paradigm. It was a full partner, a third pillar of molecular biology, with a different conception of molecular organization, and different experimental systems. I will demonstrate this by analysing the characteristics of the Britten-Davidson model of gene regulation proposed forty years ago.