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Fig. 1. Cell divisions during the fast phase of GBE are predominantly oriented
along the anteroposterior axis. (A) Side-view diagram illustrating
the process of germband elongation (GBE). Images (C-F) were taken from the
dorsal side of the embryo (eye icon). Notice how the posterior tip of the
germband (red) moves towards the anterior of the embryo (left side).
(B) Cell-division angles were measured relative to the ventral midline.
(C-F) Cell divisions during the fast and slow phases of GBE. Examples
of snapshots taken after 5 minutes (C) and 10 minutes (D) (during the fast
phase), and at 45 minutes (E) and 50 minutes (F) (during the slow phase) are
shown. The time when the pole cells become visible on the dorsal side was
arbitrarily taken as t=0. Note how cell divisions tend to be
longitudinally oriented during the fast phase (white lines).
(G,H) Quantification of cell division angles during the two
phases of GBE. The fast phase occurs during the first 25 minutes, whereas the
slow phase takes place during the subsequent 70 minutes. A total of 50 and 100
cell divisions were counted (per embryo) for the fast and slow phases,
respectively. Each bar represents the average obtained from five embryos. The
standard error is also shown. Longitudinal divisions are predominant during
the fast phase of GBE (white lines in D). A, anterior; P, posterior.
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