Fig. 5: Interactions between somites and the neural tube in hTLS and embryos.

a, Schematic diagram of the reciprocal signalling environment of the embryo (left) and hTLS (right). RA, retinoic acid; IM, intermediate mesoderm; LPM, lateral plate mesoderm. b,c, Somite-specific ALDH1A2 expression adjacent to the neural tube, in 120 h ZO-1::mEGFP hTLS (n = 4) (b) and E9.5 mouse embryo (n = 3) (c). d, Schematic of the RARE reporter cassette (top; diagram adapted from the LipExoGen website) and its functional validation upon RA addition in 2D cultures of clonal (C5 and C7) and polyclonal DR5/RARE reporter (middle) and control cells lacking the DR5/RARE elements (bottom). Prom, promoter; BSD, blasticidin selection domain; Enh, enhancer. e, The 120-h hTLS structures made with RARE reporter cell lines or control lines, with the addition of ALDH1A2 antibody staining (n = 1–8, Z-step, 2 µm and averaging eight images). f,g, Wnt signalling inhibition through IWP2 and XAV393 and resulting effect on elements of the RA (f) or Wnt (g) signalling pathways in 144-h LaminB1::mTagRFP-T (n = 6–8 per condition). Scale bars, 50 μm (b–e), 100 μm (f and g). Asterisks indicate somites; the dashed line outlines the hTLS.