Fig. 1. Anti-Pby crossreacts with Prd, Gsb and Gsbn. Drosophila embryos are stained with anti-Pby (A-J) and gene-specific monoclonal antibodies (mAbs) against Prd (K-T), Gsb (U-AA) and Gsbn (BB-EE). (A-J) As anti-Pby reacts to Prd, Gsb and Gsbn protein, the Pby pattern is a fusion of the Prd, Gsb and Gsbn patterns, as well as an additional glial pattern appearing at stage 13. (K-T) At stage 4 Prd is expressed in an anterior broad stripe (K), which itself resolves into stripes 1 and 2 as it is joined by stripes 3-7 (L). During stage 5, the primary stripes resolve into a segmental pattern of 14 secondary stripes of alternating intensity as an anterior dorsal domain appears (M). By stage 10, Prd stripes are mostly absent, but the protein persists in the gnathal protuberances (Q-T). (U-AA) At stage 7, Prd and Gsb are expressed in a coincident pattern (N,U), although Gsb stripes persist through stage 10, at which time they restrict to the neuroectoderm (X-Y). (BB-EE) Gsbn is expressed in a defined neuroectodermal pattern at stage 10, and persists after the neural stripes of Gsb have diminished. The Prd-specific MAb DP201 has not been previously described. Staining in the gnathal protuberances (Q-T) is also present in G,I but is not apparent because focal planes are sagittal. Anterior is towards the left and all views are lateral, except F,H,J,P,R,T,W,Y,AA,CC,EE, which are ventral views.