Blood island erythropoiesis is inhibited by noggin, an antagonist of BMP signaling.

Normal chicken embryos were isolated at stage 4 and were cultured according to New19 technique for 24 hours, followed by benzidine staining. Shown are representative embryos cultured in control medium (A) or noggin-conditioned medium (B). Embryos are oriented anterior to the top, with a ventral view. Original magnification × 32.