Figure 8

Neuroblast X, the cap and trail 9 (left side of the brain) in double-pulse experiments (48-h interval between the pulses) with the S-phase markers BrdU (first pulse, red) and EdU (second pulse, green) combined with immunolocalization of tyrosinated tubulin (white); late POI and early POII stages. (A, B) Both panels show the same specimen but (B) shows only the red label for the first pulse. Labeled cells in trail 9 and cluster 9 have only incorporated the first label and are not cycling anymore during the second pulse. (C) This specimen was a POI during the first pulse and hatched to POII during the 48-h chase period before the second pulse. The cap is already transforming into the medial proliferation zone (MPZ; compare Figure 14). The cells in trail 9 show only the first label (red) whereas most cells in the lateral proliferation zone (LPZ) and MPZ show both labels and therefore appear yellow. This suggests that cells in trail 9 may be post-mitotic and on their way to differentiation in cluster 9. Note strong crosstalk of the white channel (tubulin) and the green channel so that stream 10 and several nerve roots appear green instead of white. Stream 10 (str10) is devoid of any mitotic cells. The inset in (C) shows an overview of the ventral side of a brain in a further advanced POII stage showing the arrangement of the LPZ, and trail 9. Scale bars: 20 μm (A, B), 50 μm (C), 200 μm (C inset).