 mRNA at the 0000-cell stage, a stage after zygotic transcription has initiated. This suggests that a large maternal pool of unprocessed Vg0 is not essential for Nodal-Vg0 heterodimer formation and function in mesendoderm induction. Additionally comment on the sufficiency of Nodal-Vg0 production in the YSL, which may have been previously performed with Nodal. Is the zygotic marginal domain of 