Fig. 2. Embryonic expression of mkp3 in zebrafish. (A-P) Lateral views, except in D and Q-T, animal view. (A) mkp3 is not expressed as a maternal transcript, but is initiated at the high stage (B). (C,D) At 30% epiboly, expression marks the margin. (E-H) During somitogenesis stages, mkp3 is restricted to domains where FGF genes are expressed, such as anterodorsal head, the MHB, rhombomere 4 and the caudal region. (I) Comparison of mkp3 (orange) with the ventral marker, vega2/vent (blue). (J-P) mkp3 expression is regulated by FGF signaling. (J-L) Sphere stage. Inhibition of FGF activity via ectopic expression of XFD, a dominant-negative FGF receptor, suppresses mkp3 expression (K), while hyperactivation of the FGF pathway through the expression of fgf8 induces an expansion in mkp3 expression (L). (M-P) 24 hpf. Expression of mkp3 is lost in the MHB (arrows) in ace, a fgf8 mutant (N), and in noi, a pax2.1 mutant (P). (Q-T) mkp3 expression is regulated by the RAS/MAPK pathway. The mkp3 3'UTR was used to detect endogenous mkp3 expression at 30% epiboly in uninjected (Q), DNRas-(R), mkp3-(S) and DNAkt (T)-injected embryos. mkp3 expression was suppressed in DNRas and mkp3-injected embryos, but was unaffected in DNAkt-injected embryos.