Rab11 is required for myosin II activation, but does not affect apicobasal polarity. Four-cell embryos were unilaterally injected with Rab11 (2 ng, a) or Rab11S25N RNA (1 ng, b) or Rab11 MO (c-f), and cultured until neurula stages. Transverse cryosections of the neural groove (stage 17-18) are shown. * indicates the injected right side, marked by the lineage tracer GFP-CAAX RNA (50 pg, green, a, b) or GFP RNA (50 pg, green, c-f). a-c, Myosin II activation was assessed by pMLC-specific immunostaining. Rab11S25N (b, b’) and Rab11 MO (c, c’), but not wild-type Rab11 (a, a’), inhibit apical pMLC staining (red), as compared to the uninjected side. No significant effect is observed on ZO1 (d), aPKC (e) and Sox3 (f). Scale bar is 20 μm (a-f). Asterisk indicates lack of apical pMLC. M, midline position. These results are representative from 4-7 independent experiments.