Up to the present time the function and significance of the zona pellucida in the development of mammalian eggs has not been fully explained. Zona-free mouse eggs will develop in vitro from the 2-cell stage, or later, up to the blastocyst stage (Tarkowski, 1961; Mintz, 1962; Gwatkin, 1963). Single blastomeres isolated at the 2-cell (Mulnard, 1965), 4and 8-cell stage (Tarkowski & Wróblewska, 196...

Up to the present time the function and significance of the zona pellucida in the development of mammalian eggs has not been fully explained. Zona-free mouse eggs will develop in vitro from the 2-cell stage, or later, up to the blastocyst stage (Tarkowski, 1961; Mintz, 1962; Gwatkin, 1963). Single blastomeres isolated at the 2-cell (Mulnard, 1965), 4and 8-cell stage (Tarkowski & Wróblewska, 196...

A new DNA ligase activity is expressed when the Axolotl eggs enter cleavage. The messenger RNA can be labelled by [3H] uridine thereby indicating its de novo synthesis. This new genetic expression is occurring just before cleavage and is the earliest found during Amphibian development. The newly synthesized [3H] mRNA can be translated in vitro in the rabbit reticulocyte lysate system. The resul...

1. A cell-free system capable of using oxygen with oxalacetate as substrate has been prepared from both unfertilized and fertilized sea urchin eggs. The oxygen uptake by this system is about twice that of an equivalent quantity of intact unfertilized eggs and half that of an equivalent quantity of intact fertilized eggs. 2. The oxygen consumption of this cell-free oxidative system can be stimul...

In mammalian eggs, glycogen may well play an important role as an energy source during cleavage. Although the presence of glycogen in rat and rabbit eggs and the fluctuation of its concentration during development have been reported (ISHIDA 1954, 1963), histochemical demonstration of enzymes related to glycogen metabolism has not yet been published. Studies of glycogen metabolism are generally ...