USM 501 of the Museum, a mixed CNRS research unit known as UMR 7221, is located at 7 rue Cuvier, in the 5th arrondissement of Paris.

Our research is situated in the framework of the analysis of the evolution of endocrine regulations, in particular in post-embryonic development. The vast and growing array of genomic tools has given rise to a new type of physiological analysis, molecular physiology, by which regulations supporting integrated responses at the level of the organism can be analysed at the molecular level.

The collective aim of our research is to better understand how the different levels (cells/molecules) of a physiological system interact to determine their deployment and to allow adaptive modifications at critical periods of development and in morphogenesis.

Our four teams have distinct but complementary approaches to achieving this common goal:

• Team 2 (led by G. Levi): Regulations during morphogenesis

• Team 3 (led by L. Sachs): Function and action mechanisms of thyroid hormone receptors

Why a comparative approach?

Put in a comparative context, these approaches enable studies on evolution to be reconciled with those in molecular biology.

While genome-sequencing projects are providing complete inventories of the regulatory proteins for various groups of species, and underlining the strong homologies between species as distant as nematodes and vertebrates, these sequences alone do not provide an index as to the specificity of function of proteins, nor of the integration of signals at different levels of regulation. It is precisely the comparative aspects bearing on the specificity and integration of these signals, above all at the level of modules of elements regulating gene expression, which are the focal point of our analytic and experimental attention.

Our conception of comparative physiology today can be seen as the study of molecular regulations and networks placed within integrated contexts or systems. As writer Georges Perec emphasised more than 20 years ago now, the analogy between a jigsaw puzzle and physiological systems:

"Initially, the art of jigsaw puzzles seems simple, slight, wholly contained within the basics of Gestalt theory: the object in question – whether it involves an act of perception, a learning process, a physiological system… is not the sum of elements that must first be isolated and analysed separately, but is an entirety… [in which] knowledge of the whole and its laws, of the entirety and its structure, could not be derived from discrete knowledge of the elements that compose it.”