Fig. 2. Myosin II is apically enriched and essential for spiracle invagination. (A) Myosin II distribution is visualised in the spiracular chamber cells using embryos expressing Myosin II regulatory light chain (Spaghetti squash) fused to GFP (Sqh-GFP). Discs large (Dlg) (red) labels the basolateral membrane at stage 11/12 and only the lateral membrane at stage 13. The images are sagittal views and brackets indicate the position of the invaginating spiracle cells. Apical is up. (B) Spiracular chamber defects in sqh^1GLC embryos (i,ii) compared with wild type; spiracular chamber cells are labelled with GFP-Actin, using the ems-GAL4 driver. In i, spiracle cells remain on the surface of the embryo; the arrowhead indicates two spiracle cells detached from the main cluster; notice that some cells fail apical constriction (cell labelled with bracket in i', which is a magnification of the rectangle in i), as opposed to other cells with a wedge shape and high accumulation of apical Actin (e.g. cell labelled with an asterisk). (ii) The arrow indicates the disrupted pattern of apical Actin in the mild class of sqh^1GLC spiracles. Scale bars: 10 µm.