A zebrafish embryo, prior to gastrulation. Fluorescent RNA in situ hybridization highlights cells that express genes involved in determining their future fate: sox32 (magenta, in cells that will become endoderm), gsc (green, in cells that will become prechordal plate), and ntl/tbxta (red, in cells that will give rise to the notochord and tail mesoderm.) Cell membranes are labeled in yellow, and DNA in blue.