Regulation of Hox protein function:insights from protein motifs and cofactors – Hox control

How animal body plans are specified is a central question in developmental and evolutionary biology. A major conclusion from animal model studies and from annotation of metazoan genomes is that a relatively small number of gene families encoding structurally related proteins underlies the amazing diversity of animal body plans, suggesting that these regulatory factors are reiteratively used for multiple purposes. This raises the issues of functional diversity - how can a single factor induce different biological outputs' - and of functional specificity - how can molecules sharing similar or identical biochemical properties nevertheless control specific developmental programs' Understanding diversity and specificity of regulatory molecules is an important challenge in developmental and evolutionary biology. Hox proteins play fundamental roles in organizing animal body plans during development and evolution, and have been associated to several human diseases. Thus the importance of Hox proteins in development, evolution and physiopathological processes is well established. In all above mentioned processes, diversity and specificity are two hallmarks of Hox protein function. The molecular bases underlying these properties are still poorly understood, with two major obstacles: the existence and the roles of interacting cofactors on one side and of intrinsic motifs on the other side. Another obstacle, now surmounted, has long been the dominant thought that a unique mode of Hox/PBC interaction (mediated by the HX intrinsic motif) governed the functional diversity and specificity of Hox proteins. The present proposal aims to tackle the issue of specificity and diversity of regulatory molecules, taking the Hox transcription factor as a paradigm. We will investigate how intrinsic (polypeptide motifs) and extrinsic (cofactors) determinants contribute to Hox protein activity regulation. The general objectives aims to: 1/ Decipher at mechanistic and structural levels novel Hox-PBC interaction modes; 2/ Uncover general principles underlying Hox protein function; 3/ Open new entry points in the study of the regulation of Hox protein activity. We feel that recent advances in the field, some from our lab, offer the possibility to tackle this old but still unresolved issue in an innovative and original manner from conceptual and methodological points of view. Conceptually, the project aims to integrate two important dimensions, the roles of intrinsic (Hox protein motifs) and extrinsic (cofactor) determinants. These two dimensions are fully complementary: intrinsic motifs likely provide interfaces with cofactors, and cofactor identification will help understanding how a polypeptide motif contributes to Hox protein activity; motif identification will help addressing the molecular details of a given Hox/cofator interaction, and in a long term assessing the structural bases for the interaction. Methodologically, the project combines various performing technologies. This includes structural approaches to decipher the molecular details of novel Hox-PBC interaction modes, large scale (genome-wide) and small scale (molecules-, motif- and gene-specific) analyses to unravel novel general principles underlying Hox protein function, and recent imaging technologies to screen the whole genome for novel Hox cofactors.