Fig. 4. BMP depletion causes ventral mesoderm to acquire dorsal fates, animal caps to become neural, and primordial germ cell losses. (A) RT-PCR analysis of Bmp4/Bmp7-depleted VMZ explants. Microinjections of Bmp4/7 MOs cause VMZ to adopt a DMZ fate with upregulation of neural markers, such as Ncam, N-Tubulin, Otx2, and dorsal midline markers, like Shh and Xnot. (B,C) Histological sections of control VMZ compared with Bmp4/Bmp7-depleted VMZ. Absence of Bmp4/Bmp7 signaling in VMZ induces massive cell proliferation accompanied by muscle differentiation (mu), and neural tissue (ne) and cement gland (cg) formation. Insets show external views of the explants. en, endoderm; epi, epidermis; m, mesothelium; c, coelomic cavity; lpm, lateral plate mesoderm. (D-G) Animal caps depleted of Bmp4, Bmp7, or both, contain neural tissue as shown by the expression of N-Tubulin, a marker of differentiated neurons (n=12 per experimental set). (H) RT-PCR analysis of animal cap (AC) explants. Inhibition of Bmp4/Bmp7 results in neural differentiation in animal caps as shown by the expression of Ncam and Otx2 in the absence of mesodermal marker -Actin. ODC provides a loading control and Xag is a cement gland marker. (I-L) Germ cells, marked by the probe Xpat (small dots in the endodermal region), fail to develop in embryos injected with Bmp2/Bmp4/Bmp7 MOs. Primordial germ cells still form, albeit in reduced numbers, in Bmp4 or Bmp4/Bmp7 MO-injected embryos (n=8 per experimental set).