Fig. 3: Nodal propagates by a relay mechanism.

a Schematic of relay model. Senders (red outline) represent induced cells that express Nodal. Solid line with arrowhead, represents Nodal positive autoregulation. Dashed line with arrowhead represents juxtacrine induction by Nodal. Nodal/Activin signaling transducers Smad2/3 (green) are located in cytoplasm in the absence of ligands. In the presence of Nodal or Activin, Smad2/3 translocate to nucleus, and Nodal transcription is upregulated. Nodal mRNA is shown as magenta solid circles. b–d Experimental test of the relay model. b Staining of Smad2/3 to measure Nodal signaling activity in juxtaposition experiments with cells with the indicated genotypes. Signal is nuclear when the pathway is activated. Sender cells in all conditions were labeled by mCherry-CAAX. Images in each case taken after 20 h juxtaposition n = 4, scale bar, 20 µm. c, d Experiments performed as in (b) and Nodal mRNA (NdlRNA) was measured. Nodal RNA was quantified as a function of distance from border (n = 4 for each condition) (c) Representative images of 9 h and 20 h post-juxtaposition is shown, scale bar, 50 µm. d Nodal RNA was measured in a separate experiment with 9 h and 20 h post-juxtaposition. iWT means induced wild type cells, iNKO means induced Nodal KO cells. Data are presented as mean values + /− SEM, n = 4 biological replicates.