Ribosomal RNA Synthesis in Sea Urchin Embryos: Differential Rates of Accumulation in Chemically-induced Animalized...

Animalization was induced with evans blue and with Zn++ in embryos of Arbacia punctulata and of Lytechinus variegatus, respectively. Li+ induced vegetalization in A. punctulata embryos. While animalization did not affect the rate of cleavage, vegetalized embryos exhibited a reduction in cell number at post-morula stages. Mid-gastrulae and corresponding experimental embryos each were labeled for 4 hr with uridine-[5-3 H] and with L-[3 H-methyl]-methionine. The rate of uptake of each exogenous RNA precursor was similar in control and in experimental embryos. Purified RNA preparations were fractionated by electrophoresis on 2.4% acrylamide+0.5 % agarose gels. Comparison of rates of incorporation of each RNA precursor into 26s and 18s RNAs indicated that on a per cell basis evans blue- and Zn++ -animalized embryos showed a reduction (0.53-0.56) and Li+ -vegetalized embryos an enhancement (1.41-1.53) in the rate of accumulation of newly made 26s and 18s RNAs compared to controls (1.00). These results suggest that chemically-induced animalized and vegetalized embryos provide useful tools for studying possible differential gene expression in different embryonic germ layers of the developing sea urchin embryo.