title: Involvement of contractile proteins in the changes in consistency of oocyte nucleoplasm of the newt Pleurodeles waltlii.
abstract: In the present work, we show that actin is present in considerable quantities in the oocyte nucleus of the newt Pleurodeles waltlii. The nuclear sap, extracted in saline buffer containing Ca++, is fluid. DNAase I inhibition assays have shown that 90% of actin is under a globular state in such conditions. Chelation of Ca++ by EGTA leads to the formation of a nuclear gel composed of individual microfilaments. This nuclear gel contains approximately 50% of total nuclear actin in a filamentous form. Phalloidin, a drug known to stabilize F-actin, induces the formation of a network of actin cables in the nuclei. This network contains nearly 100% of total nuclear actin in the filamentous form. The observation of the cables in the electron microscope shows that they are made of tightly associated microfilaments to which RNP-like particles are bound. The actin antibodies stain the cables and the particles by the indirect immunoperoxidase technique; myosin antibodies mainly stain the particles. The formation of the phalloïdin-induced network seems to require the presence of Ca++, Mg++, and ATP. We propose a scheme for the regulation of the supramolecular forms of actin in oocyte nuclei in which a delicate equilibrium seems to exist between globular actin, microfilaments, and actin cables. This equilibrium would be controlled by the concentration of Ca++, ATP, and various actin-associated proteins.
mesh_terms: D000199:Actins / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002467:Cell Nucleus / Q000032:analysis / Q000648:ultrastructure*; D055598:Chemical Phenomena; D002621:Chemistry; D003599:Cytoskeleton / Q000502:physiology*; D005260:Female; D046911:Macromolecular Substances; D009865:Oocytes; D010590:Phalloidine / Q000494:pharmacology; D010999:Pleurodeles / Q000502:physiology*; D012455:Salamandridae / Q000502:physiology*
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D010590:Phalloidine; D000255:Adenosine Triphosphate; D002118:Calcium