The transcriptional repressor Snail is required for proper differentiation of the tail muscle of ascidian tadpole larvae. Two muscle lineages (B5.1 and B6.4) contribute to the anterior tail muscle cells, and are consecutively separated from a transcriptionally quiescent germ cell lineage at the 16- and 32-cell stages. Concomitantly, cells of these lineages begin to express () at the 16- and 32-cell stages, respectively. Meanwhile, expression begins in these two lineages simultaneously at the 32-cell stage. Here, we show that expression is regulated differently between these two lineages. In the B5.1 lineage, was activated through , which is activated by maternal factors, including Zic-r.a. In the B6.4 lineage, the MAPK pathway was cell-autonomously activated by a constitutively active form of Raf, enabling Zic-r.a to activate independently of As a result, begins to be expressed at the 32-cell stage simultaneously in these two lineages. Such shortcuts might be required for coordinating developmental programs in embryos in which cells become separated progressively from stem cells, including germline cells.