Pulses of Notch activation synchronise oscillating somite cells and entrain the zebrafish segmentation clock.
Formation of somites, the rudiments of vertebrate body segments, is an oscillatory process governed by a gene-expression oscillator, the segmentation clock. This operates in each cell of the presomitic mesoderm (PSM), but the individual cells drift out of synchrony when Delta/Notch signalling fails, causing gross anatomical defects. We and others have suggested that this is because synchrony is maintained by pulses of Notch activation, delivered cyclically by each cell to its neighbours, that serve to adjust or reset the phase of the intracellular oscillator. This, however, has never been proved. Here, we provide direct experimental evidence, using zebrafish containing a heat-shock-driven transgene that lets us deliver artificial pulses of expression of the Notch ligand DeltaC. In DeltaC-defective embryos, in which endogenous Notch signalling fails, the artificial pulses restore synchrony, thereby rescuing somite formation. The spacing of segment boundaries produced by repetitive heat-shocking varies according to the time interval between one heat-shock and the next. The induced synchrony is manifest both morphologically and at the level of the oscillations of her1, a core component of the intracellular oscillator. Thus, entrainment of intracellular clocks by periodic activation of the Notch pathway is indeed the mechanism maintaining cell synchrony during somitogenesis.
Vertebrate Development and Developmental Genetics Laboratories, Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3LY, UK.
Cristian
C
Soza-Ried
Emre
E
Öztürk
David
D
Ish-Horowicz
Julian
J
Lewis
D000818:Animals; D030801:Animals, Genetically Modified; D001683:Biological Clocks; D002452:Cell Count; D004625:Embryo, Nonmammalian / Q000378:metabolism; D018869:Heat-Shock Response; D018398:Homeodomain Proteins / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051881:Receptor, Notch1 / Q000378:metabolism*; D019170:Somites / Q000166:cytology* / Q000378:metabolism*; D013997:Time Factors; D019076:Transgenes; D015027:Zebrafish / Q000196:embryology / Q000378:metabolism; D029961:Zebrafish Proteins / Q000378:metabolism*
D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D051881:Receptor, Notch1; D029961:Zebrafish Proteins; C064045:delta protein; C437805:notch1a protein, zebrafish
Delta; Notch; Oscillation; Segmentation clock; Somites; Zebrafish