FIGURE 4.

Hinge point formation depend on proper somitic mesoderm morphogenesis. (A) Dorsal view of a representative neurula stage 16 embryo stained with Phalloidin (F-actin). Red arrows: F-actin accumulation at the neural plate boundary denotes hinge point formation. Purple arrows: Hinge point formation is impaired at the neural plate side overlying Wee2 morphant somitic medoderm. Asterisk: Side overlying Wee2 morphant somitic mesoderm. Scale bar: 100 μm (B) Normalized F-actin intensity profile along the mediolateral neural plate axis. n = 10 embryos. Peak intensity indicates the position of the hinge point. Note that F-actin accumulation at the side overlying somitic mesoderm injected with Wee2 morpholino is impaired. Inset: Representative example of neural plate of an embryo with unilateral Wee2 morphant somitic mesoderm. Asterisk: Wee2 morphant side. Purple box was used to plot F-actin intensity profile along the neural plate mediolateral axis. Scale bar: 100 μm (C) Quantification of hinge point formation. χ² test; ****p < .0001 n = 15 embryos. (D) Stills from a time lapse recording of a neurula embryo expressing Utrophin GFP. Green dotted line: midline. Cyan arrows: Neural plate surface ectoderm boundary at the side overlying control somitic mesoderm. Red arrows: Neural plate/surface ectoderm boundary at the neural plate side overlying Wee2 morphant somitic mesoderm. F-actin accumulation characteristic of hinge point formation occurs only at the neural plate/surface ectoderm boundary overlying control somitic mesoderm Scale bar: 50 μm.