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Fig. 5. Establishment of the compartments for future neural subdivisions at stage
16+. (A) Location in embryo and size of the cell groups later contributing to
distinct cephalic divisions, color-coded according to
Fig. 3. Lateral view of tel-,
di-, mes- and rhombencephalon, and spinal cord cell groups from stage 16+ (a)
to stage 24 (f). Animal pole on the top and dorsal side on the right. White
and red broken lines outline the boundaries for future neural subdivisions.
The cell groups for tel-, di- and mesencephalon are displaced anteriorly
without changing their AP length, while those for rhombencephalon and spinal
cord elongate along the body axis. (B) Measurement of cell movement within
cell groups. (a) Horizontal planes across the CNS-forming cell mass to measure
cell movement along the AP axis. The planes were drawn on a computer graphics
embryo model, so that planes 3 and 8 are placed at the position corresponding
to the boundaries at stage 16+ between diencephalon- and mesencephalon-forming
cell groups (plane 3) and between mesencephalon- and rhombencephalon-forming
cell groups (plane 8). Other planes were drawn at intervals of 40 µm,
corresponding to a two-cell width distance. (b) Number of cells crossing the
transverse planes (1-10) in an hour was counted at stages indicated. (c)
Number of cells crossing the midline at the stage indicated. (C) Occurrence of
mitotic cell divisions giving rise to split fate daughter cells. Divisions
that produced daughter cells that contributed to different neural subdivisions
at stages 13-17 are indicated by two colored rectangles of the color code, as
in Fig. 3. Numbers on the top
indicate the split cell fate division in each stage. (D) Proliferation of
labeled cell populations in cell groups that contributed to particular neural
subdivisions at stage 24. Increase in cell number is robust between stage 17
and stage 19, but thereafter becomes moderate except in retina.
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