CONTRACTILE PROTEINS AND NONERYTHROID SPECTRIN IN OOGENESIS OF XENOPUS-LAEVIS

The distribution of contractile proteins, actin and myosin, and an act in-binding protein, spectrin, was studied in oogenesis of Xenopus laev is. These proteins are present in oocytes already at the previtellogen ic stages, which are characterized by their diffuse distribution. The localization of proteins changed with the beginning of vitellogenesis. At all vitellogenic stages, including the fully grown oocyte, animal- vegetal differences were noted in localization of actin and myosin: in the animal hemisphere they appear as fibrillar-like structures, while in the vegetal one they are localized around the yolk platelets. By t he end of the oocyte's growth, a cortical gradient appeared: predomina nt localization of actin and myosin in the cortical area. As the oocyt e maturation proceeded, the distribution of actin and myosin again bec ame diffuse and nonuniform, so that a cortical gradient appears. At th e beginning of vitellogenesis spectrin is distributed as a network all over the ooplasm, while in the fully grown oocyte it is localized mos tly in the subcortical area of the animal hemisphere and, as individua l inclusions, in other regions of the oocyte. No spectrin is found by the end of maturation. Actin, myosin, and spectrin are also present in the oocyte's nuclei. Changes in the distribution of contractile prote ins and spectrin during oocyte maturation are discussed with respect t o the development of cortical contractility, as well as to the changes in spatial distribution of yolk platelets and regional sensitivity of the maturing oocyte to cytochalasin B. (C) 1994 Wiley-Liss, Inc.