The Synthesis and Localization of Envelope Glycoproteins in Oocytes of Xenopus laevis using Immunocytochemical Methods

Abstract

Development Growth & DifferentiationThe site of origin and the mode of differentiation of the coelomic envelope (CE) in growing oocytes of Xenopus laevis were studied using the rabbit antiserum raised against the isolated envelope from oviposited eggs. The antiserum preabsorbed with egg extracts reacted with most components of CE glycoproteins detectable by SDS-PAGE, and stained specifically the CE of full-grown (st. VI) oocytes using indirect immunofluorescence methods. Transmission electron microscopy employing IgG-conjugated colloidal gold demonstrated that the CE antigens were distributed throughout the whole cytoplasm of st. I oocytes, and began to be deposited around the oocyte surface at late st. I. During st. II to VI the density of CE antigens in the oocyte cytoplasm decreased markedly, while the deposition of extracellular CE antigens increased gradually in association with the formation of a fibrillar network. The CE antigens were observed in and around the highly extended oocyte microvilli during st. II to IV, but were never found in follicle cells at any stages of oocyte growth. On western blot analyses, the extracellular CE components appeared first at st. II, and increased both in amount and number of bands during st. Ill -V to attain a typical electrophoretic profiles of well-developed CE. The cytosols of growing oocytes, however, possessed several antigenic components which were distinct from those of extracellular CE, suggesting the occurrence of intracellular precursor molecules for CE. The CEs of st. IV oocytes defolliculated and cultured in [3H] leucine contained certain CE components that expressed the radiolabel on fluorography. These results indicate that in Xenopus laevis the oocyte is directly involved in the synthesis and assembly, as well as secretion of CE with least contribution by the follicle cells.

Zona pellucida protein ZP2 is expressed in the oocyte of Japanese quail (Coturnix japonica)

“…In most mammalian species including mice, there is clear evidence showing that ZP glycoproteins are synthesized by the growing oocytes (Bleil & Wassarman 1980). In X. laevis, they are also expressed in the oocytes (Yamaguchi et al 1989). In addition to the oocytes-restricted expression, the follicular granulosa cells also contribute to the synthesis of ZP3 in rabbits (Lee & Dunbar 1993) and in cynomolgus monkeys (Martinez et al 1996).…”

Molecular characterization of egg envelope glycoprotein ZPD in the ovary of Japanese quail (Coturnix japonica)

“…Although no ZPD homolog has been identified in mammalian species, the expression of ZP glycoproteins appears to be regulated differently in different species. There is clear evidence showing that ZP3 is synthesized by the oocytes themselves in mice (Bleil & Wassarman 1980) and in Xenopus (Yamaguchi et al 1989), whereas the granulosa cells in the follicles also participate in the formation of ZP3 in rabbits (Lee & Dunbar 1993) and in cynomolgus monkeys (Martinez et al 1996). On the other hand, a glycoprotein homologous to ZP3 in chorion, the fish egg envelope, is produced in the liver and transported to the ovary by the blood circulation, like vitellogenin (Hamazaki et al 1985(Hamazaki et al , 1989.…”

Untitled

“…However, TEM studies employing IgGconjugated colloidal gold revealed that vitelline envelope antigens were distributed throughout the whole cytoplasm and began to deposit around the surface of the stage I oocyte. 22 This study indicated that the cytoplasm of the stage I oocyte already contained components reactive with anti-vitelline coat antibodies 22 , thus suggesting that the oocyte may play a major role in synthesizing its own vitelline envelope.…”