Fig. 2

Spiral embryogenesis in P. dumerilii: Linking lineage to gene expression and fate cell-by-cell. a Early stages of the P. dumerilii embryo. The mitotic spindles are labeled with anti-alpha-tubulin antibody (green), the actin with rhodamine phalloidin (magenta), and the nucleus with DAPI (blue). Arrows show the direction of cell division. The zygote first divides into AB and CD cells (2-cell stage) and after the second cleavage A, B, C, and D cells are generated. The subsequent spiral cleavages with alternating division axes lead to a 64-cell stage embryo with A, B, C, and D quadrants (described in Hsieh 2020 [70]). b–b’’’ P. dumerilii cell lineage with 4d lineage highlighted. Mesoderm (shades of blue), germline (magenta), and mesodermal posterior growth zone (8ML) arise from the 4d lineage. b’’ The segmental mesoderm blocks that arise from this lineage are shown with respect to the larval schematic (b’’’) (modified from Özpolat et al. 2017). c–e’ Cell lineage-specific markers (e’ is modified from Wilson 1892, Bastin et al. 2015, Vopalensky et al. 2019) Otx (c,) and fzCRD-1 (c’) expressing cells at 12 hpf were aligned onto the live-imaging movie of a Platynereis embryo used for constructing the anterior cell lineages (d). d’ A subset of the cell lineage from b is shown (*). Otx, which patterns neuronal tissues, and fzCRD-1, which labels a pair of kidney-like cells, are differentially expressed in daughter cells from the same founder cells, 1cd1122. The progeny of the otx-expressing daughter cell will continue to divide and form neurons while the fzCRD-1 expressing daughter cell will cease dividing and differentiate into a kidney-like cell. e At 24 hpf, fzCRD-1 is expressed in two elongated cells that correspond to the pair of kidney-like cells originally observed by E. B. Wilson in his foundational work on P. megalops and Nereis cell lineages in 1892 [53 (arrowheads in e’)