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Fig. 1. Characterization of the S-phase in pIIa and pIIb precursor cells (A-C) and
pIIIb precursor cells (D-F). A strategy combining time-lapse imaging (A,D) and
BrdU incorporation (B,E) was used to define the duration of the S-phase in
these cells. (A,D) Time-lapse analysis of living
neuP72> H2B::YFP pupae at 17 hours APF (A) and 19 hours
APF (D). Time (h:min) before the end of the time-lapse recording is shown at
the top of each frame. (B,E) BrdU incorporation in the same clusters as in A
and D, respectively (numbered from 1 to 4). BrdU incorporation is revealed in
red, and lineage cells were identified by specific anti-Sens immunoreactivity
(green). In B, the time following the end of the corresponding pI metaphase,
determined by time-lapse recording, was 19 minutes for cluster 1, 27 minutes
for cluster 2, 59 minutes for cluster 3 and 1 hour 56 minutes for cluster 4.
Note that both precursor cells exit the S-phase at the same time, as suggested
by the punctuated BrdU labelling (B, cluster 3). In E, the time after the end
of the corresponding pIIb metaphase was 7 minutes for cluster 1, 19 minutes
for cluster 2, 39 minutes for cluster 3 and 1 hour 15 minutes for cluster 4.
Note that BrdU incorporation was observed only in the pIIIb cell, recognized
by the size of the nucleus and its anterior position in the cluster. (C,F)
Histograms showing the percentage of BrdU-positive clusters as a function of
time after pI (C) and pIIb (F) metaphase. Black bars correspond to cell pairs
in which BrdU incorporation was homogeneous throughout the nuclei. Hatched
bars correspond to cell pairs in which punctuated BrdU incorporation was
observed. Note in F that no BrdU incorporation was observed before 15 minutes
after pIIb division. In both histograms, bars were calculated after analysis
of at least 5 clusters. Scale bar: 2 µm.
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