Fig. 3. Polyadenylated RNA is transcribed prior to midblastula transition (MBT) in intact embryos. (A) Total RNA transcribed in early embryos was detected by injection of -[³²P]UTP in two-cell embryos, which were then cultured with or without actinomycin D (ActD). RNA was prepared from various stages prior to MBT and analyzed by electrophoresis on an agarose gel, followed by autoradiography. The upper panel is an autoradiograph showing newly synthesized RNA and the lower panel shows ethidium bromide-stained ribosomal RNA from the same samples. (B) Newly synthesized polyadenylated RNA was purified by binding to oligo-dT cellulose followed by agarose gel electrophoresis and autoradiography. An equal amount of poly-A+ RNA from the 2000-cell sample was treated with RNaseA prior to loading (+RNase). Equal amounts of polyadenylated RNA were loaded in each lane, as judged by ethidium bromide staining (not shown).