Figure 4.
BMP1 CUB domains bind BMP4 growth factor. (A) Diagram of BMP1 and BMP1 CUB1/2 constructs and their mutations. (B) Mimicking an antimorph revertant mutant in BMP1 (DN-BMP1WR) or BMP1 CUB1/2 impairs protein secretion. (C–E) Overexpression of DN-BMP1 dorsalized embryos (note the enlarged head marked by Otx2), but the second site revertant mutation (DN-BMP1WR) had no effect. (F) BMP4 binds to full-length BMP1 on a BIAcore sensor chip. (G) Purified BMP1 CUB1 and CUB2 domains are sufficient for BMP4 binding. (H,I) Embryos injected with BMP1 CUB1/2 RNA were dorsalized, as indicated by the expanded Otx-2 expression domain (n = 83, 81% dorsalized). (J) Dorsalization (anti-BMP) effect was also observed after injection of BMP1 CUB1/2 purified protein into the blastula cavity (n = 85, 82% dorsalized).