Fig. 2. U0126 treatment and injections of mRNA encoding a MAP Kinase Phosphatase (MKP3) or a dominant-negative Raf (dnRAF) block PMC ingression and differentiation. (A-D) Control embryos. (E-H) Embryos treated with 10 µM U0126, (I-L) embryos injected with MKP3 mRNA, (M-P) dnRaf injections, (Q-T) dnRas injections. Note the absence of PMCs in the embryos treated with UO126 (E,F), or injected with MKP3 RNA (I,J) or dnRaf RNA (M,N). (A,E,I,M,Q) Mesenchyme blastula, (B,F,J,N,R) early gastrula, (C,G,K,O,S) late gastrula and (D,H,L,P,T) pluteus stage. anv, anal view. In control embryos, the PMCs ingress into the blastocoel (A) and form a ring around the archenteron and two bilateral clusters during gastrulation (B).