[Formation of the gray crescent, induced in axolotl oocytes during maturation, depends on factors of nuclear origin].

Inhibitors of protein synthesis caN elicit the precocious appearance of a grey crescent (GC) in in vitro maturing Ambystoma mexicanum oocytes. This treatment however fails to induce GC formation when the oocytes are enucleated before initiation of maturation. The ability to form a GC is reestablished in enucleated oocytes by the injection of nucleoplasm from a normal oocyte, either before or after injection of the inhibitor. In the latter case, the GC appears even though the protein synthesis level is already about one-tenth that of the control enucleated oocytes. One or several nuclear factors, in conjunction with protein synthesis inhibition, are therefore essential for the early symmetry reaction. The corrective nuclear factor is already present in the germinal vesicle of young oocytes at the very beginning of vitellogenesis. It is not species-specific and enucleated axolotl oocytes can be symmetrized with Pleurodeles or even Xenopus oocyte nucleoplasm. The interaction between nuclear factor(s) and cytoplasm is possible only when cytoplasmic maturation has occurred.