Fig. 6

Developmental expression patterns of ancestral early patterning genes. a–c Representative developmental expression of six3 (a), nk2.1 (b), and otx (c) between 12 and 30 hpf. d The expression of the three genes otx (blue), six3 (green), and nk2.1 (red) mapped on the lineage movie at 12 hpf and the clonal offspring of these cells visualized at later stages. Cells expressing both six3 and nk2.1 are labeled in orange. e Whereas the otx and nk2.1 clonal domain reflects the lateral regions adopting bilateral symmetry very early (compare to Figs. 5A' and 7D), the six3 domain encompasses the medial region with later and lineage-unrelated origin of bilateral symmetry (compare to Fig. 7C and D). f Visualization of cell age (time from the last division) at 30 hpf reveals the prototroch and the apical organ as the earliest differentiating regions of the episphere (compare to expression of the neural markers in Additional file 12: Figure S3). g Analysis of the lineage depth (the number of preceding cell divisions of a given cell, starting from the zygote until the given time point) identifies the lateral regions as the most proliferative in accordance to the shortest cell cycle length (h)