During development, the posterior brain undergoes a transient segmentation process along the anteroposterior axis leading to its subdivision into 7 transversal units called rhombomeres (r) that form developmental and genetic expression units. The zinc finger factor plays a key role in this process by coupling the formation and the specification of the rhombomeres 3 and 5. Three regulatory elements controlling Krox20 expression have been characterized previously. Elements B and C are active in r5 and in r3-r5, respectively, and are involved in the onset of Krox20 expression whose amplification and upkeep are carried out by the autoregulatory element A. Thus, element C is a key tool to investigate the mechanisms responsible for the regionalized expression of Krox20 in r3. In order to deepen the characterization of Krox20 transcriptional control in r3, I undertook a functional analysis of the sequences of element C by mutagenesis and identified several conserved blocks required for its activity in r3. Furthermore, I established the complete quantitative and differential transcriptomic map of the mouse early hindbrain by RNA-Seq and I characterized several regulators of element C activity. Finally, I analyzed the mouse mutant where element C is deleted and I revealed new properties of Krox20 transcriptional control, notably a cis-cooperation between elements A and C. As a conclusion, this work shows how the combination of different approaches allows the elucidation of a complex transcriptional regulation mechanism that plays an essential role in cell specification
