RNA: a marker in embryonic differentiation.

A modified fluorochrome technique which identifies nucleic acids differentially in tissues permits following production of RNA in the embryo. Compact primordial chick embryo cells show a sequence to RNA production as differentiation begins: First in the nucleus, then in the perinuclear area, then in the cytoplasm. RNA increases in the cytoplasm with cell growth and continues as the cells merge to form an epithelium.