The ventral to dorsal BMP activity gradient in the early zebrafish embryo is determined by graded expression of BMP ligands

► The zebrafish ventral to dorsal BMP activity gradient is established by 40% epiboly. ► Graded expression of BMP ligands precedes the formation of the activity gradient. ► There is no evidence that BMP2B protein diffuses to form the BMP activity gradient. ► The BMP activity gradient is determined by graded ligand expression. ► Graded bmp2b transcription is due to temporal regulation by Dharma, FGF, and Chordin.