Fig. 6. The Gro- and CtBP-binding motifs of H are each required for its full activity in promoting the SOP cell fate. (A) Half of a wild-type fly head showing the three macrochaete bristles of the orbital region (boxed; magnified in inset). (B) Expressing wild-type H (via UAS-H) in non-SOPs with an E(spl)m-Gal4 driver converts some of these cells to SOPs, producing ectopic bristles that are either normal (white arrow) or display a `double shaft' phenotype (black arrow) due to a cell fate conversion in the bristle lineage (Barolo et al., 2002) (black arrowhead indicates another double shaft broken during manipulation). (C) Frequency of supernumerary orbital bristles observed in adult flies carrying one copy of E(spl)m-Gal4 driving expression of wild-type H (one copy of UAS-H), H lacking its CtBP-binding motif (UAS-HC), H with its Gro-binding motif mutated (UAS-H[Gm]) or H lacking both motifs (UAS-H[Gm]C). Two different insertions of each UAS construct were tested (#1, #2).