Fig. 7. FGFA is required for activation of ERK in lateral ectodermal regions whereas ERK is required for expression of sprouty and pax2/5/8 in sea urchin. (A-D) Control or MoFGF-injected embryos were processed for whole-mount immunolocalization of activated ERK using an anti MAPK-P antibody (A,C) or for in situ hybridization using a sprouty probe (B,D). (E-J) Embryos at the mesenchyme blastula stage were treated or not with the MEK inhibitor U0126 for 6 hours and processed for in situ hybridization using the indicated probes.