||FIG. 3. Increased activated MAPK expression was observed to completely surround the blastopore at mid- to late gastrula stages (A,
arrowhead indicates dorsal). (B) A sagittal section of staining in a late gastrula embryo (dorsal is on the right and the animal pole is up).
Specifically, increased staining occurs in the presumptive mesoderm (pm) and posterior neural tissue (pn) but expression is lost in the
involuted mesoderm (im) and is not present in the anterior neural tissue (b, brain). During neurula stages (posterior staining of stage 17
shown here in C and D) activated MAPK expression remains localized to posterior as well as anterior regions of the embryos. (C and D)
Anterior on the right and posterior to the left. In a sagittal section through the midline of the embryo, posterior staining was specifically
seen in the posterior mesoderm (pm, notochord) and neural (pn) tissue (D). Scale bar, 300 mm.