A Multi-cell, Multi-scale Model of Vertebrate Segmentation and Somite Formation
(A–F) Experimental images from Kulesa and Fraser , taken at 0, 25, 50, 80, 100 and 110 minutes (reproduced with authorization). Scale bar 50 µm. (G–M) Snapshots of a simulation reproducing the “ball and socket” morphology described by Kulesa and Fraser , taken at 0, 15, 30, 45, 60, 85, 100 and 190 minutes. Scale bar 40 µm. Initially, a “sleeve” of cells that will eventually be posterior to the forming border cradles presumptive somite cells that will eventually be anterior to the forming border (A–C, G–J). As the intersomitic border continues to develop, these two populations of cells move relative to each other to position themselves on the appropriate sides of the border (D–E, K–M). The “sleeve” then retracts, leading to a rounded intersomitic border (F, N). The white and red dots in the simulations correspond to those in the experimental images. (O) Confocal image of one half of the PSM in a live chick embryo at HH Stage 10, stained with the cell-surface lipid label BODIPY ceramide. (P) Simulation detail at the corresponding time point. Simulated morphology closely resembles that observed in vivo, including the initially narrow gap separating adjacent somites (white circles), the block-like shape of the newly forming somite, the gradual rounding of more mature somites, and the resulting notch-like intersomitic clefts at the medial and lateral edges of maturing somites (red circles). Another notable feature of the simulation is the persistence of misplaced cell types after differentiation (white arrow heads). Model cell type colors are identical to those in Figure 5. Scale bars 50 µm. Reference simulation parameters: segmentation-clock period = 90 min; PSM growth rate = 1.63 µm/min; Table 4 (FGF8 and Wnt3a); Table 3 (cell-cell adhesion); Table 2 (cell sizes and motility); and Table S1 (segmentation clock).