Fig. 1

Overview of early spiral cleavage and live imaging of the developing episphere. a The early development of a prototroch larva by spiral cleavage. The apical quartet of micromeres 1m (light red) present at 8-cell stage gives rise to the episphere, whereas the quartet of macromeres 1M (gray) gives rise to the hyposphere. The precursors (1m-2) of the prototroch cells are labeled in yellow. For 66-cell stage, a schematic apical view (top) together with a corresponding snapshot (bottom) of the nuclear signal in the time-lapse recording of the developing episphere is shown. The colors of the nuclear tracks in the snapshot correspond to the coloring in the schematic apical view. The dashed blue line represents the border between embryonic quadrants. Apical views modified from [9]. The ventral views are extensively schematized for simplicity. b Left-hand panel shows the overview of time-lapse recordings used for the analysis of the cell lineage. Asterisks mark the movies used to create the consensus lineage tree (Additional file 10: Figure S2). The reference lineage movies RefLin1 (Additional file 3 and RefLin2 (Additional file 6) were assembled from 3 or 2 recordings, respectively, schematized by the colored bars along the timeline. To perform temporal calibration of the movie frames to developmental time, total nuclei in the episphere of at least three fixed specimens for each indicated stage (5, 10, 12, 14, 16, 20, 24, and 30 hpf) were counted (plotted in the right-hand panel, error bars represent the standard deviation of the mean, n = 3)