Fig. 7. Spg/Pou2 is a maternally provided regulator of DV patterning. Schematic top view of blastula embryos. Arrows indicate a regulatory relationship that need not be direct. pou2 is required upstream of maternal TGFß/Bmp signaling to activate ventral-specifying genes such as bmp2b, bmp4 and, partially, bmp7. pou2 is also required to maintain vox, vent and eve1 from late blastula stages onwards. In addition, pou2-dependent bmp2b expression involves repression of an Fgf-dependent repressor, either at the onset of bmp2b expression or at later blastula stages. In MZspg embryos, ventral-specifying genes completely or partially fail to be initiated, causing the embryo to be dorsalized. Specifically, ventral Bmp activity fails to establish, causing ectopic expression of dorsal organizer-derived genes nog1, chd and gsc.