Fig. 5

Mitosis in the growth zone of Thamnocephalus. a Scoring pH3-positive cells (black columns) in the growth zone captures consistently higher numbers of cells in M-phase compared to cells measured with nuclear staining (gray columns, Hoechst). Mitosis rates are highest just after hatching and increase prior to the first molt (dotted line). b Regardless of developmental stage, ~ 80% of the actively dividing cells (Hoechst) in the growth zone are oriented along the AP body axis. c Total calculated number of cells in the growth zone (black columns) compared to average number in mitosis (red) at successive developmental stages. (For comparison, the first red column is pH3 positive cells the second Hoechst. pH3 data were not collected after 12 h and the averages for the Hoechst scored mitotic figures drop to 1 and 2.) d Representative photo of AP-oriented cells in the GZ (arrows) in an early larva, although not stained with Engrailed, the approximate position of the last En stripe is indicated (asterisk). Note the medial–lateral oriented cells in the developing segments (arrowhead). Scale bar equals 100 µm