Figure 4.

Axial tissues exert a pushing force on the PD

(A) Layout of the model showing simulated ablations (boxes) corresponding to results in (B). Empty arrow, an axial cell; filled arrow, a PSM cell. See also Movie S4.

(B) Axial elongation speeds (±SEM) for both before and after tissue ablation. For PD, cell addition was disabled in the beginning of simulation. Speeds were averaged over 2000 time points in each simulation. Each experiment includes n=40 simulations. p=0.93, control; p<0.05, other groups (paired t-tests).

(C) Net forces along AP experienced by an axial cell and a PSM cell. The cells start at the same AP level as marked in panel (A). Positive indicates A to P. Data points are binned by 200 iteration windows. Curves: 4 times moving average.

(D) Gel replacement of PD followed by confocal timelapse. Green indicates spots of DiI injection to follow cell movements. Spots in the pPSM can be seen expanding while the axial tissues narrow. Scale bar: 200μm.

(E) Quantified shape changes of the gel implant in (D). Consistent observations in n=3 embryos.

(F) Contours of the gel implant in (D). Asterisk highlights the indentation where the gel is in contact with pNC.

(G) Summary of gel replacement experiments. The l/w ratios after 2–3 hours are plotted as a percentage of the initial aspect ratio. Tissue names indicate implant locations (e.g. pNC, PD), “+/−“ indicates further perturbations (e.g. Blebbistatin treatment [+Bleb.], pPSM ablation [-pPSM]). Asterisks: p<0.05, t-tests. n.s.: p=0.4. See also Figures S3O–P.

(H) Shape change and cell dispersion of PD transplant. A group of GFP+ progenitors (shown in red) is transplanted posterior to the pNC of cherry+ host (shown in green). Arrows: cells in the transplant disperse into host pPSM. Anterior flattening of the transplant and cell dispersion were observed in n=4/6 similar experiments. Scale bar: 100μm.