Ultrastructure of Xenopus laevis oocytes after injection of an extract from progesterone-treated oocytes

Abstract

When the supern atan t of a cen trifuged homogen ate from progesteron etreated oocytes is injected into Xenopus full grown oocytes, an in complète and abnormal maturation called "pseudomaturation" occurs. The first sign of pseudomaturation is observed in the cortical région: the plasma membrane becomes lobulated and pièces of cortical cytoplasm are shed into the médium. The most remark able ultrastructural characteristic of pseu domaturation is the hyperdevelopment of the internai membranous System, characterized in particular by the extensive growth of the endoplasmic reti culum, the maintenance of numerous annulate lamellae, unusually slow to disappear. The pores of the latter are often aligned and characteristicaliy united by columns of partially fibrillar materiai. Before the break down of the germinal vesicie, sheets of fibrillar materiai appear at intervais in the cytoplasm, mainly around the nuclear membrane. The basai part of the nuclear membrane undergoes extensive folding before break down of the germinal vesicie occurs; the nuclear membrane usually ruptures near the apical pôle. The main altération in the nucleus is a rapid condensation of the fibrillar core of the numerous nucleoli; the fibrillar and the granular parts of the nu cleoli segregate; they are often found associated with bundles of 340 Â micro tubules. Chromosome condensation is never observed. Several attempts have been made to analyze the mechanisms of amphibian oocyte maturation, in particular hormonal stimulation and the rôles played, respectively, by the nucleus and the cytoplasm (75, 20). Maturation can be induced, in full grown Rana pipiens or Xenopus laevis oocytes, by addition of progestérone to the médium (i, 19). According to Masui and Mark ert (75), maturation can also be induced in large Rana pipiens oocytes by injecting cytoplasm tak en from oocytes which have undergone maturation after progestérone treatment. The présence of a maturation

Nuclear pore complex assembly studied with a biochemical assay for annulate lamellae formation.

“…Such stacks were common in the pellet. In agreement with the results of others, we did not detect any pore-containing membranes at t = 0', confirming that intact NPCs were not being introduced by any of the individual components of the reaction mixture (Steinert et al, 1974;Kessel and Subtelny, 1981;Imoh et al, 1983;Larabell and Chandler, 1988;Bement and Capco, 1989;Dabauvalle et al, 1991).…”

“…AL reconstitution, as discussed earlier, represents a simplified system for studying nuclear envelope and pore formation in the absence of chromatin. It had been demonstrated that while annulate lamellae are abundant in the cytoplasm of Xenopus oocytes, fully mature eggs and extracts harbor no pore-containing membranes (Steinert et al, 1974;Kessel and Subtelny, 1981;Imoh et al, 1983;Larabell and Chandler, 1988;Bement and Capco, 1989;Dabauvalle et al, 1991). During meiotic maturation of the oocyte, AL respond to mitotic signals in a manner similar to the nuclear envelope and, therefore, disassemble.…”

Induction of maturation (meiosis) in Xenopus laevis oocytes by three organomercurials.

“…Injection of a homogenate from progesterone-treated oocytes induces, in recipient oocytes of Xenopus laevis, an abortive and highly abnormal maturation that we have called pseudomaturation (4,12,13); the homogenate thus contains, besides MPF, a "pseudomaturation inducing factor" (PIF). While MPF is localized in the endoplasm and stimulates protein synthesis in injected recipient oocytes, PIF is located in the cortical layers of the donor oocytes and is a powerful inhibitor of protein synthesis (4,12).…”

Localization by situ hybridization of amplified ribosomal DNA during Xenopus laevis oocyte maturation (a light and electron microscopy study).

“…They had already been described hn previous work (12) Application of the methods used in the present paper to later stages of development (unfertilized, fertilized, and cleaving eggs) might provide useful information about the fate of rDNA after maturation. The significance of the mitochondrial envelope which surrounds the nucleolar organizers after they have been cast out into the cytoplasm remains obscure: they might conceivably play a role in their eventual further degradation or in their apparent absence of replication during segmentation (13,14).…”