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Fig. 4. Loss of longitudinally oriented cell divisions in segmentation
mutants. (A-D) Pattern of cell divisions in an eve mutant
embryo at 7 (A), 10 (B), 70 (C) and 75 (D) minutes after the onset of
elongation. (E,F) Quantification of cell-division angles during
0-25 minutes. Out of the 260 cell divisions assessed (from five embryos), no
significant longitudinal bias can be seen (E). For this data set, cell
divisions were separately analysed in the medial (blue) and lateral (red) half
of each hemisegment (F). A total of 130 mitoses were assessed for each domain.
Some longitudinal bias can be seen for divisions occurring in the medial
region (blue in F). Mild compensatory transversal bias in the lateral domain
(red) might explain the lack of overall bias seen in E. (G)
Quantification of cell division orientation during the 26-96 minute time
period. Here, 150 divisions from five embryos were assessed. As in wild type,
no longitudinal bias can be seen. (H-K) Orientation of cell divisions
in embryos laid by bicoid nanos torso-like (BNT) females. Because
these embryos do not undergo germband extension, the posterior region was
observed from the ventral side of the egg. The portion of the embryo within
view is shown as a white outline in the bottom right corner, with the double
line indicating the ventral furrow. The first post-blastoderm divisions appear
random in orientation (K; 150 divisions were assessed in three embryos) and
cause an isotropic increase in tissue size (I,J). This increase reverts as
other regions of the embryo undergo divisions, giving an impression of
pulsatile behaviour in time-lapse recordings (see Movie 5 in the supplementary
material).
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