Fig. 1. Effects of removing msh: symmetric ventral-ventral wings. (A) Cuticle preparation of a wild-type wing. AWM, anterior wing margin; L2-L5, longitudinal veins 2-5. (B,C) Detailed views of dorsal structures of the wing in (B) wild type and (C) msh mutant clones. (Upper panels) Anterior wing margin (AWM); (center panels) alulas; (lower panels) veins. (B) In the wild type the AWM differentiates three rows of bristles. Two are dorsal (d); a row of thick mechanosensory bristles adjacent to the compartment boundary and a row of thin curved chemosensory bristles. The ventral row (v) is composed of thin bristles interspersed with chemosensory bristles in every fifth position. A schematic representation of the AWM is shown below. Red circles denote dorsal bristles, big circles indicate mechanosensory bristles and small circles indicate chemosensory bristles. Filled circles denote the chemosensory bristles located in the ventral surface, and open circles the mechanosensory bristles. (Center panel) The alula has a single row of bristles on the ventral surface and no dorsal bristles (not shown). (Bottom panel) Magnification of the dorsal side of vein L3. Corrugation of the L3 vein is asymmetric on dorsal (d) and ventral (v) surfaces of the wild-type wing. The corrugated surface (indicated in red in the diagrams at bottom) consists of 2-3 rows of more darkly pigmented cells. The opposite surface consists of one row of cells. In wild-type wings, veins L3, L5 and the distal part of L4 are corrugated dorsally and veins L2 and proximal L4 are corrugated ventrally. (C) Mutant clones were generated in f³⁶ hs-FLP (I); FRT 82 msh⁶⁸/FRT 82 P(f+) larvae. msh mutant cells were marked with forked. In the AWM small arrows indicate the clone. The blue arrows indicate chemosensory bristles and large arrowheads indicate dorsal bristles outside the clone. A schematic representation of the AWM mutant for msh is shown below. Both surfaces differentiate ventral bristles (v). (Center panel) Magnification of an alula covered with clones mutant for msh shows that both dorsal and ventral surfaces differentiate bristles. (Lower panel) Magnification of the dorsal side of vein L3 shows part of the clone mutant for msh (red arrows); wild-type cells in the vein are indicated by black arrows. Note the transition from dorsal to ventral corrugation as shown in the diagram at the bottom.