Fig. 1a, b.

Compartmental boundaries in Drosophila. a In the Drosophila imaginal wing disc, lineage restriction boundaries form between anterior (A) and posterior (P) compartments (orange and blue, respectively), as well as between dorsal (D) and ventral (V) compartments (dark and light shades, respectively). The Notch receptor is activated in the cells immediately ventral and dorsal to the D/V boundary (yellow stripe). b In Drosophila stage 8–11 embryos, anterior and posterior compartments meet at two interfaces in each metameric unit. The anterior-posterior interface is the parasegmental (PS) boundary, while the posterior-anterior interface (P-A boundary) corresponds to where segmental folds will form later in embryogenesis. Only parasegmental boundaries are lineage restriction boundaries. a, b Red and gray dashed lines represent lineage restriction boundaries and morphogen-dependent boundaries, respectively. Transcription factors are shown in black, components of cell-cell signalling pathways in red and adhesion molecules in pink. Arrows indicate the relationship between the genes involved in compartmentalization. N Notch, Fng Fringe, Ap Apterous, Trn Tartan, Caps Capricious, En Engrailed, Hh Hedgehog, Dpp Decapentaplegic, Cad99C Cadherin 99C, Wg Wingless