Figure 2.

Cell autonomy of PCP signalling within the neural keel. (a-b) Whole-mounts and transverse sections through the trunk of 24 hour post-fertilization WT (a) and MZtri (b) embryos injected with 100 pg of lefty mRNA. Convergence of the neural plate into a neural rod occurs normally in WT+lefty embryos, despite the absence of underlying mesendoderm (a'). This convergence is disrupted in MZtri+lefty mutants, which show neurulation defects in the absence of trunk mesoderm (b'). Brackets in a and b indicate the extent of trunk axial extension. Identical results were obtained using a different genetic combination: maternal-zygotic one-eyed-pinhead (MZoep) mutants were used to eliminate Nodal signalling, and PCP signalling was perturbed through diego mRNA injection (not shown). (c) mGFP-labelled MZtri cells were transplanted into MZoep host embryos at mid-blastula stages to generate MZtri->MZoep chimeric embryos. MZoep mutants lack Nodal signalling and do not form endoderm or trunk mesoderm lineages²⁹, therefore endoderm and trunk somites in chimeric embryos develop entirely from GFP-positive MZtri donor cells. (c') Transverse sections of 24 hpf MZtri->MZoep chimeras were counter-stained with rhodamine-phalloidin to visualize neural tube formation (outlined in c'). The absence of MZtri neurulation defects indicates a requirement for PCP signalling autonomous to the neuroectoderm. (d-g) Transverse sections through the trunk of WT and MZtri chimeric embryos at 24 hpf. (d) Bilateral distribution of mRFP-labelled WT cells (arrowheads) within the neural tube of an mGFP-labelled WT host. (e) Unilateral accumulation of mRFP-labelled MZtri cells within the neural tube of mGFP-labelled WT host embryos. (f-g) mRFP-labelled MZtri (f) or WT (g) cells transplanted into mGFP-labelled MZtri host embryos accumulate unilaterally within the MZtri neural anlage. Scale bars, 50 μm.