Fig. 8. Tld activity mirrors Dpp concentration helping to create a sharp boundary in signal reception. The graphs illustrate proposed temporal changes within the dorsal half of the embryo in the extracellular concentrations of Dpp and Sog as development proceeds from early to late cellular blastoderm. The green circles below the black line represent cells receiving Dpp signal. The darker green indicates a higher level of cumulative signal received over the entire time span. Yellow and orange represent cells receiving low level of Dpp signal because of early blockage in Dpp signaling by Sog diffusion. Red circles represent Sog-expressing cells. The embryos at the right show P-Mad accumulation with time. Embryos were stained using PMad primary antibody at 1/1000 dilution and anti-rabbit HRP at 1/200 dilution. The embryos were developed for 20 minutes.