Ribosomal RNA Synthesis in Sea Urchin Embryos: Differential Rates of Accumulation in Chemically‐induced Animalized and Vegetalized Larvae

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Abstract
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‐[5‐3H] and with L‐[3H‐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.