The segmented pattern of the vertebrate spine is established during embryogenesis by the formation of somites (blocks of mesoderm that form the vertebrae and back muscles) at regular temporal intervals. In the clock and wavefront model for somitogenesis, pulses of Notch, FGF and Wnt signalling in the presomitic mesoderm (PSM) are translated into the periodic array of somites at the so-called wavefront. Olivier Pourquié and colleagues now provide the first genetic evidence that FGF signalling positions the wavefront and controls the segmentation clock in mouse somitogenesis (see ). They show that conditional deletion of the FGR receptor gene Fgfr1 in the mesoderm abolishes FGF signalling and disrupts normal cyclic gene expression in the PSM. It also arrests somite formation. In addition, pharmacological inhibition of FGF signalling blocks the oscillations of both Wnt and Notch signalling in the PSM, but with different kinetics. The researchers conclude,therefore, that FGF signalling acts upstream of Wnt and Notch signalling to control the segmentation clock during mouse somitogenesis.
