Fig. 5. Dominant-active T559D Moesin expression prevents photoreceptor apical regionalization. (A,B) Electron micrographs of 65% pd wild type (A) and hs>T559D Moesin Myc (B) ommatidium. The apical membrane, spanning between adherens junctions (A,B; arrows), is severely disorganized by T559D Moesin expression (B). In this ommatidium (B), R5 is less affected, showing clear rhabdomere and stalk domains, presumably due to lower levels of T559D Moesin expression. (C,D) The apical actin cytoskeleton is severely disrupted in dominant-active Moesin-expressing cells, and Crumbs (C) does not properly relocalize to the stalk. (D) The field in C, showing Crumbs staining (blue) merged with staining for F-actin (red) and Myc (green). Red rhabdomeres of `escaper' cells, not expressing T559D Moesin Myc, appear normal. (E) The ommatidium marked with an asterisk in D is shown at a higher magnification. T559D Moesin was not expressed equally in all cells in this ommatidium, as reflected by the lack of Myc staining in the asterisked R7. F-actin in the rhabdomere of R7 is orderly, and Crumbs was properly cleared from the rhabdomere membrane and localizes to the stalk. Compare with neighboring photoreceptors in D. Scale bars: 1 µm in A,B; 10 µm in D.