Fig. 1. Widerborst is a B' subunit of PP2A required for planar polarization. (A) Wild-type wing epithelial cells each make a single hair. (B) Driving expression from EP3559 on the dorsal wing blade with Apterous GAL4 causes multiple wing hairs to form. (C) Expression of a cDNA (LD3434) corresponding to CG5643 (the locus downstream of EP3559) produces a similar phenotype. (D) Dendritic tree depicting the relationships between different PP2A B' subunits from fungi (Sp T11663, Sp Ydd2, Sc Rts.1, Nc CAC28812.1), C. elegans (Ce C13G3.3a, Ce RTS.1), Drosophila (Dm CG7901, Dm Wdb), Xenopus (Xl B' ), zebrafish (zWdb1, zWdb2) and Homo sapiens (Hs B' , ß, , and ). The bar in the upper right -hand corner depicts the branch length corresponding to 0.05 amino acid substitutions per residue. (E) Location of EMS mutations within the Wdb transcript, and structure of the Wdb dominant-negative construct. Grey regions are non-coding. The red region is strongly conserved between all members of the B' subfamily. Green indicates sequences conserved only between Widerborst and the and subfamily members. Blue indicates divergent sequence unique to Widerborst. Arrows indicate the positions at which, wdb^dw, wdb¹², wdb¹⁴, and wdb^IP are mutated and the resulting sequence changes. wdb^dw and wdb¹² probably cause short N-terminal truncations (see Materials and Methods) because they make protein that is detectable with an antibody against the C terminus. (F) The ventral wing blade of a wdb^dw/wdb^IP transheterozygote shows regions where hair formation fails or is compromised. Stunted hairs are often misoriented (arrows). (G) The ventral wing blade of a fly that expressed dominant-negative Wdb along the anteroposterior compartment boundary, under the control of PatchedGAL4. The expressing region is indicated in red. Expressing cells form hairs that are stunted and misoriented. Occasionally, hairs fail to form. Posterior to the expression domain, hair formation and orientation are affected non-autonomously (asterisk and arrows). (H) The ventral wing blade of a fly that expressed dominant negative Wdb along the anteroposterior compartment boundary (red). Even hairs of normal morphology display orientation defects.

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