Fig. 3.

Summary of key landmarks in OSM development. (Details are within Figs S1-S3). (A-D) Cartoons showing the location and morphology of the A7.6 descendants, or trunk lateral cells (TLC) at 5.5, 8.5, 13 and 16 hpf. The anterior-most TLC derivatives, which give rise to the OSM, are shown with green cytoplasm for emphasis. (A′-D′) Micrographs showing the same time points, with TLC marked by MyT>H2B::mCherry (A′) or LexO(A7.6)>>H2B::mCherry (B′-D′). At 5.5 hpf, expression of Hand-related is restricted to the anterior daughter of the A7.6 blastomere (A′). Two cell divisions later, Ebf is activated exclusively in the anterior-most TLC, all of whose descendants we will call the anterior TLC (aTLC) (B′). After one more cell division, Tbx1/10 is activated in the anterior-most aTLC, the OSM founder cell (OSMF) (C′) and is maintained in both daughter cells, the OSM precursors (OSMP) (D′). (E,F) At 18 hpf, Isl>YFP (E) and Mrf (F) are both expressed in the OSMP. TLC marked by LexO(A7.6)>>H2B::mCherry. (G) Schematic diagram showing complete clonal relationships between all TLC until 8.5 hpf, and of the anterior TLC, which are all cells descended from A10.48, after 8.5 hpf, with gene expression mapped on. Onset and duration of gene expression is indicated by the colored bars above the dendrogram; gene expression is indicated in each cell also by color. Open arrowhead, aTLC; white arrows, OSMFs and OSMPs. Scale bars: 20 μm.