Fig. 3. Rho1 is essential for spiracle invagination. (A) Wild-type Filzkörpers. (B) Cuticle of a null mutant for Rho1 (Rho1^1B) showing irregular Filzkörpers (arrows). (C) Severe class of Rho1^1B embryos, with one uninvaginated Filzkörper. (D) GFP-Actin (green) distribution in the spiracular chamber of wild type and Rho1^1B/Rho1^72R mutants (stage 17); red, Filzkörper autofluorescence obtained with the 488 nm laser. In wild-type spiracles, a continuous line of Actin surrounds the Filzkörper, while in late Rho1 mutants this pattern is partially lost. (E,F) Expression of the dominant negative form of Rho1, RhoN19, impairs Filzkörper secretion (E) and the invagination of spiracle cells (F, arrow); green, GFP-Actin. (G,H) Wild-type spiracle and a spiracle in which RhoN19 has been expressed visualised with GFP-Actin. Expression of RhoN19 disrupts the accumulation of apical Actin (arrowhead), while elongation of the basolateral membrane is still observed (arrow). Scale bars: 10 µm.