RNase A activity in Japanese quail oocytes

The presence of RNase A activity was studied in vitro in homogenates of quail oocytes and early embryos using [3H]poly(U) as a substrate. The activity was measured by adsorption of the undegraded substrate onto DE-81 filter paper discs and by chromatographic separation on a Sephadex G-50 column. RNase A activity examined by these methods was almost undetectable in quail previtellogenic, vitellogenic and ovulated oocytes as well as in the embryos from laid eggs. It is estimated to be about 1.1 x 10(-5) Kunitz units per ovulated oocyte. Higher activity starts to appear in gastrulating embryos. These findings are discussed in relation to other studies demonstrating the high stability of maternal RNA during early development, especially in growing oocytes.