Fig. 1. SoxB1 protein encoded from mRNA microinjected at the one-cell stage does not persist in vegetal cells. (A) Translation of SoxB1 mRNA is efficiently blocked in embryos that develop from zygotes injected with SoxB1MO, as shown by the absence of staining with an antibody specific for SoxB1 (green, compare with B and C). Red staining detects the 6e10 extracellular epitope produced by primary mesenchyme cells. This embryo is at the temporal equivalent of prism stage but has failed to differentiate an archenteron (Kenny et al., 2003). (B) Co-injection of the SoxB1 morpholino and MO-immune SoxB1 synthetic mRNA rescues differentiation of gut and coelomic rudiments (white arrowheads). SoxB1 protein translated from the microinjected mRNA (green) accumulates and persists in the ectoderm, but does not persist in secondary mesenchyme (white arrowheads) or endoderm (except for low levels in the foregut). (C) An embryo at the hatched blastula stage treated as in B also clears SoxB1 protein (green signal, left) from vegetal blastomeres, despite the fact that the microinjected mRNA is present in them, as shown by whole-mount in situ hybridization to SoxB1 mRNA in the same embryo (blue signal, right). The embryo is stained for SoxB1 (FITC) and DNA (DAPI); the merged fluorescent signals over SoxB1-positive nuclei are blue-green, whereas those of SoxB1-negative nuclei are blue. Immunofluorescence images are shown on the left; DIC images, right. A and V indicate animal and vegetal poles, respectively. Scale bars: in B, 20 µm for A,B; in C, 20 µm.