Comparison of brain organization and expression of key developmental genes involved in CNS regionalization and MHB formation in vertebrates and Drosophila. Data for Drosophila reflect the situation at stage 11, data for vertebrates reflect the situation in mouse at about embryonic day 10 (E10; see ; Nkx2.2, ; Msx3, ; the data for Bts1 are from a comparable developmental stage in zebrafish ). The boxed area coloured in light red indicates the neuroectodermal region around the MHB in vertebrates, according to the expression domains of Pax2,5 and 8 and En1 and 2. Although early Pax2/5/8 gene expression is lacking in Drosophila, the corresponding box may indicate a similar domain around the otd/unpg border. Identical colours indicate orthologous genes. Vertebrate gene names in red indicate those genes that are not or differently expressed at the Drosophila otd/unpg interface. For details, see the text. PC, DC, TC; proto-, deuto-, tritocerebrum; MD, MX, LA, mandibular, maxillary, labial neuromere, respectively; SOG, subesophageal ganglion. Di, Me, Te, Dien-, Mesen-, Telencephalon, respectively; r1-8, rhombomeres 1-8.