Fig. 4

Fate mapping reveals that olig2-expressing neural plate cells give rise to primary motor neurons and oligodendrocytes (A) Dorsal view of living 10.5-hpf embryo in which caged fluorescein was photoactivated in a stripe of neuroectoderm overlying one edge of the notochord (notochord boundaries marked by white arrows). (B) Dorsal view of fixed 10.5-hpf embryo in which caged fluorescein had been photoactivated similarly to embryo in (A) and probed for olig2 RNA expression. Larger bracket indicates olig2-expressing cells, which are blue. Smaller bracket indicates cells in which caged fluorescein (fl) was photoactivated, revealed by red staining. Photoactivated cells are within the olig2 expression domain. (C) Side view of 19-hpf embryo probed for isl2 expression (blue) to reveal primary motor neurons and processed to reveal photoactivated fluorescein label (red). Photoactivated cell is a primary motor neuron (arrow). (D) Transverse section of 48-hpf embryo processed to reveal photoactivated fluorescein (red) and sox10 expression (blue). Arrow indicates double-labeled oligodendrocyte progenitor that originated in medial neural plate. (E) Transverse section of 72-hpf embryo processed to reveal photoactivated fluorescein label (red,arrow). Labeled cell occupies dorsal white matter, indicating that it is an oligodendrocyte, which originated in medial neural plate. Scale bar, 20 μm.