Fig. 1.

Localization of Ci-MRF transcripts during embryogenesis shown by in situ hybridization. (A) Vegetal views of transcript distribution in cleavage, gastrula, and neural plate stage embryos. The developmental stage is indicated in each panel; arrows in the 110-cell embryo and early gastrula embryo indicate A8.16 cells that have neural and muscle fates. Only cells on one side of the bilaterally symmetrical embryo are labeled in each panel. Labels on the neural plate stage embryo indicate muscle (A9.31) and neural (A9.32) precursors; in order to distinguish these cells, this embryo was stained with Hoechst dye. Approximate ages of embryos in hours after fertilization, when reared at 18°C are 44-cell (3.75 hr), 64-cell (4.25 hr), 76-cell (4.5 hr), 110-cell (5 hr), gastrula (6 hr), neural plate (7 hr). (B) Diagram of the primary muscle lineage; cells that are fate restricted to form muscle are shown in red. Numbers at the top of the diagram indicate the cell-stage. (C) Vegetal and lateral views of Ci-MRF transcript distribution in a single neurula-stage embryo (~8 hr post fertilization at 18°C). (D) Lateral (upper row) and dorsal (lower row) views of Ci-MRF transcript distribution during tail formation; Orientation of each embryo is anterior (top, left), posterior (bottom, right). Approximate developmental ages at 18°C are 9 hr (Early), 11 hr (Middle) and 13 hr (Late). Abbreviations are A (anterior), P (posterior), An (animal), Vg (vegetal), ep (epidermis), N (notochord). All scale bars are 50 μm.