Schematic of embryonic DV patterning. From an initially transcriptionally inert nave embryo (nuclear cycle (nc) 79, 6080 min (min) after egg laying (AEL)), a dorsoventral (DV) nuclear gradient of the maternally supplied transcription factor Dorsal (Dl) (nc 1013, 1.52.5 hours (h) AEL) specifies cell fates at zygotic genome activation (ZGA) (nc 14, 2.53.5 h AEL). Distinct transcriptional programs initiated by the absence of Dl dorsally, moderate nuclear Dl laterally, and high nuclear Dl ventrally lead to cell specification into dorsal ectoderm, neuroectoderm, and mesoderm, respectively. Disrupted Dl gradient formation in Toll signaling mutants produces embryos composed entirely of presumptive dorsal ectoderm ( gd 7 ), neuroectoderm ( Toll rm9/rm10 ), and mesoderm ( Toll 10B ).
