A 2-COMPONENT CYTOSKELETAL SYSTEM OF XENOPUS-LAEVIS EGG CORTEX - CONCEPT OF ITS CONTRACTILITY

The cortex of Xenopus laevis eggs comprises two components: the plasma membrane with underlying microfilaments (external layer) and the cyto plasmic matrix with embedded pigment granules (internal layer). Both c omponents of the egg cortex ape capable of contracting under the influ ence of calcium ions. The cortex of the fully grown oocyte does not ha ve the ability to contract, but acquires it during progesterone-stimul ated maturation, when the oocyte is transformed into an egg. It has be en proposed, on the basis of the data on the cortex cytoskeletal organ ization, that the submembranous microfilaments form an anisotropic net work in the oocytes, which is transformed into an isotropic, randomly organized network in the egg. The latter is capable of contractile act s. Reorganization of the cytoskeleton in the internal cortex layer lea ds to the formation of the actin contractile gel. Data are provided on the role of actin-associated proteins in changes of organization of t he actin cortical cytoskeleton. Mechanisms underlying the different se nsitivity of microfilaments of the internal and external layers to cyt ochalasin B, as well as the coordinated (in time) development of the c ontractility in these layers, are discussed. The model proposed for de velopment of the cortical contractility during oocyte maturation (Ryab ova et al., 1994a) is considered on the basis of a two-component cytos keletal system.