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Fig. 6. Inhibition of Bmp2/Bmp4/Bmp7 signaling in UV-treated embryos or
ß-Catenin-depleted embryos results in radial brain formation.
Bmp2/Bmp4/Bmp7 MOs were injected four times radially (12 ng each) into
two-cell-stage UV-irradiated embryos, or were co-injected with ß-Catenin
MO (7 ng total) (n=45 or more per experimental set). White arrowheads
point to the blastopore/anus. (A,B) Depletion of Bmp4/Bmp7 in wild-type
embryos leads to tail defects, but leaves the head and trunk regions mostly
unaffected [Dorso Anterior Index, DAI=6.6
(Kao and Elinson, 1988)]. (C)
UV-treated embryos are radially ventralized and develop into ventral `belly
pieces' lacking all CNS and head structures (DAI=0.7). They are devoid of
neural tissue, as shown by the lack of Sox2 expression at stage 20
(inset). (D) UV-treated embryos injected with Bmp4/Bmp7 MOs are radially
dorsalized, and lack trunk and tail structures (DAI=8.1). At stage 20, half of
the ectoderm of UV-treated Bmp2/Bmp4/Bmp7 morphants expresses the pan-neural
marker Sox2 (inset). (E) ß-Catenin MO-injected embryos, like UV
embryos, develop into radially ventralized belly pieces (DAI=0.3). They are
also devoid of neural tissue, as shown by the lack of Sox2 expression
at stage 20 (inset). (F) Depletion of Bmp4/Bmp7 activity in ß-Catenin
MO-injected embryos leads to dramatically hyperdorsalized embryos (DAI=9.5)
with a radial cement gland (compare with B). At stage 20, half of the ectoderm
of ß-Catenin/Bmp2/Bmp4/Bmp7 morphants expresses the pan-neural marker
Sox2 (inset). (G) Embryos dorsalized by LiCl treatment (DAI=8.6). (H)
Western blot analysis of endogenous phosphorylation of Smad1 at gastrula stage
11. Embryos ventralized by ß-Catenin MOs have high levels of Smad1
phosphorylation, which require Bmp4/Bmp7 signals.
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