Fig. 3

Fig. 3 Six1a is required for early myog expression in fast muscle precursors. Flat mount embryos after two-color WISH for myog (purple) and mespa (red) at 9 s (A, B) or single-color in situ hybridization for myog (A′, B′, C, and D), smyhc1 (E–G) or myod (H, I) at 9 s. The four posterior somites with the adjacent presomitic mesoderm are shown. Insets show the posterior part of the embryo. Arrowheads indicate the region of fast muscle precursors. Note that the myog expression is nearly absent along the entire posterior border in SIII and retained in a few medially located cells in SIV (B) and in somites shown in panel D (white arrowheads). The expression in the adaxial cells (white arrow) was retained (B and D). The hardly visible residual myog expression in the affected cells marked by asterisks. CM caused no effect on myog expression (B′). UM or SM cause no obvious effect on the expression of slow muscle-specific marker smyhc1 (F and G, 62/65 and 55/60 of embryos injected with UM or SM, correspondingly) or on myod expression in fast muscle precursors (I; 70/73 of embryos injected with SM). Scale bar, 100 μm.