3H-uridine incorporation in early porcine embryos

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Abstract
The present study investigated the ontogeny of 3H‐uridine incorporation into RNA as a measure for RNA synthesis in preimplantation porcine embryos from the two‐cell stage up to the stage of the newly hatched blastocyst. A total of 568 embryos were cultured in vitro for 3 hr in medium (KRB plus lamb serum) containing 9 μM 3H‐uridine. After disruption of cell membranes, RNA was isolated on DEAE cellulose filters, and the radioactivity was taken as a measure for the rate of RNA synthesis. No RNA synthesis was detected at the two‐cell stage. From the four‐cell to the morula stage, 3H‐uridine incorporation per embryo increased about ninefold (P < 0.001) in blastocyst stages, the increase between developmental stages was not statistically significant. Hatched blastocysts had the highest genomic activity. On a per cell basis, 3H‐uridine incorporation was not different from the four‐cell stage up to the zona pellucida‐intact blastocyst and amounted to 0.29–0.37 fmol 3H‐uridine incorporation/cell/3 hr. In hatched blastocyst, 3H‐uridine incorporation per blastomere was increased (P < 0.01 compared with younger stages) and amounted to 0.86 fmol 3H‐uridine incorporation/cell/3 hr. It is concluded that 1) the rate of uridine incorporation depends on the cell stage in zona pellucida‐intact porcine embryos and 2) uridine incorporation per blastomere is significantly increased in hatched blastocysts compared with earlier stages.