Figure 5. ActivinB Is Required for Pmar1-Mediated Endomesoderm Induction.

Embryos were injected with either 0.02 μg/μl SpHE-gfp or 0.02 μg/μl SpHE-gfp and 0.015 μg/μl SpHE-pmar1, as indicated to the left of the images. Embryos were analyzed by two-color FISH for gfp (red) and either (A) endo16 (green) at 26 h p.f. or (B) gcm (green) transcripts at 18–20 h p.f. The presence of 1.4 mM ActivinBMO1 strongly reduces both ectopic and endogenous endo16 mRNA levels ([A], i–l vs. e–h, compare arrowheads in [A] j and k vs. f and g for residual endogenous endo16 expression in the presence of ActivinMO1), but not those of the pigment cell marker, gcm ([B] i–l vs. e–h). Embryos shown are representative of more than 80% of a minimum of 50 embryos in each of three separate experiments in which gfp was detected in nonvegetal regions of the embryo. DIC images in (A) d and (B) d, h, and l illustrate the absence of detectable developmental defects in injected embryos. gfp-expressing cells containing Pmar1 in (A) h and l have adopted a mesenchyme phenotype and ingressed into the blastocoel at 26 h p.f.