Differential expression of Bmp genes in VAb@2cell embryos. (A-D) Similar expression pattern of bmp7a in intact and VAb@2cell embryos at the indicated stages. (E-H) The expression pattern of bmp4 remains unchanged in VAb@2cell embryos at 50% epiboly, but is strongly reduced at 65% epiboly. (I-L) The initiation of bmp2b expression is unaffected in VAb@2cell embryos at sphere-dome stage, but its zygotic transcription in the margin is reduced or absent at 50% epiboly. (M,N) Scattered bmp2b expression pattern in VAb@2cell embryos at 75% epiboly. Lateral views with dorsal on the right. (M′,N′) Higher magnification in the ventral-animal region of indicated embryos. (M″,N″) Localisation of bmp2b in indicated embryos. (O) Statistical analysis of bmp2b marginal expression in intact and VAb@2cell embryos at the indicated stages, with representative images shown at the top. Numbers on the top of the graph indicate total embryos from two independent experiments. (P-R) Comparison of bmp2b expression in indicated embryos at 50% epiboly. The bmp2b marginal expression is maintained or enhanced in VAb@1cell embryos, but is suppressed in VAb@2cell embryos. (S) Analysis by qRT-PCR of bmp2b levels in VAb@1cell and VAb@2cell embryos. Data are mean±s.d. from four independent experiments. (T) A working hypothesis to explain the dorsalising effect of VAb@2cell. In addition to DDs, putative BMP inhibitors and agonists are also vegetally localised. After fertilisation, the BMP inhibitors should be transported to the animal pole region more rapidly than the BMP agonists; this may account for the appearance of the dorsalised phenotype after VAb@2cell. Scale bars: 250 µm in A-N,P-R; 100 µm in M′-N″.
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