Dose response of BMP-4 plasmid for globin protein induction. Western blot analysis for globin expression in animal cap explants. Embryos were injected with 5, 20, and 200 pg of pcDNA3–BMP-4, and animal caps were explanted and cultured with or without activin (12 ng/mL) or bFGF (200 ng/mL) until sibling embryos were at stage 35. Protein extracts were made from the animal caps and separated on a SDS polyacrylamide gel. Proteins were transferred to nitrocellulose and incubated with a larval -globin monoclonal antibody. Each lane is loaded with one cap equivalence of protein extract. The finding that 5 pg of pcDNA3–BMP-4–loaded caps treated with activin (lane 2) induces more globin protein than FGF treatment (lane 3) is variable.