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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.
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