Priming, initiation and synchronization of the segmentation clock by deltaD and deltaC

Abstract

Zebrafish somitogenesis is governed by a segmentation clock that generates oscillations in expression of several Notch pathway genes, including her1, her7 and deltaC. Using a combination of pharmacological inhibition and Mendelian genetics, we show that DeltaD and DeltaC, two Notch ligands, represent functionally distinct signals within the segmentation clock. Using high-resolution fluorescent in situ hybridization, the oscillations were divided into phases based on eight distinct subcellular patterns of mRNA localization for 140,000 cells. her1, her7 and deltaC expression was examined in wild-type, deltaD(-/-) and deltaC(-/-) embryos. We identified areas within the tailbud where the clock is set up in the progenitor cells (priming), where the clock starts running (initiation), and where the clocks of neighbouring cells are entrained (synchronization). We find that the clocks of motile cells are primed by deltaD in a progenitor zone in the posterior tailbud and that deltaD is required for cells to initiate oscillations on exiting this zone. Oscillations of adjacent cells are synchronized and amplified by deltaC in the posterior presomitic mesoderm as cell movement subsides and cells maintain stable neighbour relationships.

Random cell movement promotes synchronization of the segmentation clock

“…In zebrafish, the synchronization of the segmentation clock is realized by intercellular interaction via Delta-Notch signaling (11-13, 30, 31). Previous models have confirmed that this interaction successfully leads to the synchronization of oscillation among cells (24,25,30).However, previous analyses did not answer the following questions: (i) In the actual segmentation process, dynamic rearrangement of relative cell positions due to cell proliferation and movement is observed in the PSM (12,32,33). Can the synchronization of the segmentation clock be achieved and stably sustained under such random cell movement?…”

“…However, previous analyses did not answer the following questions: (i) In the actual segmentation process, dynamic rearrangement of relative cell positions due to cell proliferation and movement is observed in the PSM (12,32,33). Can the synchronization of the segmentation clock be achieved and stably sustained under such random cell movement?…”

“…Each cell in the lattice is identified by index j (j ¼ 1; 2; …; N). In our simulation, the lattice size was chosen as 25 × 10 (N ¼ 250) unless otherwise indicated, because the tailbud region of the PSM is approximately 250 × 100 μm 2 (12) and the diameter of each cell is approximately 10 μm.…”

“…In the PSM, oscillatory expressions are synchronized among neighboring cells. This synchronized oscillation is necessary for normal segmentation, and disruption of the synchronization results in a defective somite boundary (11)(12)(13).…”

Modelling Oscillator Synchronisation During Vertebrate Axis Segmentation

“…However, mutants for different Delta ligands are observed to affect oscillation patterns in the PSM in different ways, suggesting more than the single role of synchronisation in the PSM for Notch-Delta signalling [4,5], or at the very least a complex interaction between Notch-Delta signalling components and the somitogenesis clock.…”