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Fig. 4 Spatiotemporal expression pattern of BMPR-IA. Wholemount in situ hybridization analysis at different stages; sphere stage (A,B, blastula), shield stage (C, early gastrula) and 80% epiboly (D, late gastrula). As shown in B, in the sphere stage, detectable signals were not obtained using sense probes as a negative control. Note that BMPR-IA was expressed ubiquitously during early embryogenesis. At 80% epiboly stage (D), signals were rarely detected in the ventroanimal region in whole embryos, but in sagittal sections faint signals were observed in this region (data not shown). Lateral views are oriented with their dorsal side to the right except for (A). Scale bar; 200 μm. (E) Northern blot analysis demonstrated that BMPR-IA transcripts were present at low levels maternally. Zygotically, strong signals persist during early embryogenesis with a peak at the shield stage. The positions of 28S and 18S ribosomal RNA are indicated.