Growing Xenopus oocytes have spare translational capacity.

Abstract

Previous studies have shown that exogenous mRNAs injected into full-grown (stage 6) Xenopus oocytes are translated only at the expense of endogenous messages; translational capacity is limited. In this report, we demonstrate that injection of globin mRNA into small, stage 4 oocytes results in an increase in total protein synthesis without a concomitant decrease in the translation of endogenous mRNAs. The absence of competition with endogenous messages in stage 4 oocytes injected with globin mRNA, compared with stage 6 oocytes, was not due to differential turnover of the injected mRNA. Hybridization of RNA from mRNA-injected oocytes at both stages revealed that similar amounts of globin mRNA were present. These results are interpreted to mean that protein synthesis in growing oocytes is limited by the availability of mRNA and not components of the translational machinery. This conclusion, however, does not apply to all mRNA classes. The capacity of stage 4 oocytes to translate a mRNA (zein) on membrane-bound polysomes is as restricted as reported previously for stage 6 oocytes. This result suggests that putative membrane binding sites or rough endoplasmic reticulum content are limited in oocytes at both stages. The possible role of association of injected mRNA with endogenous proteins that prevent translation is discussed.

Nucleocytoplasmic Interactions in Morphogenesis

“…A review where more than 200 références to papers dealing with mRNA translation in Xenopus oocytes can be found has been recently published by Soreq (1985). Injection of globin mRNA into young, vitellogenic oocytes is also followed by globin expression; in such oocytes, in contrast to full-grown oocytes, there is no compétition between foreign and endogenous mRNAs for the protein-synthesizing machinery (Taylor et al, 1985).…”

MS-based quantitative analysis of the CRM1 export pathway and spatial proteomics of the Xenopus laevis oocyte

“…Therefore, oocyte stockpiles huge amounts of biological material (protein, RNA, lipids) for later usage. Even though, oocyte is quite active in protein synthesis during development, it has been reported that only a portion of the ribosome is active and they are stored for later use (Taylor et al, 1985). Metabolic pathway members, particularly, glycolysis members might be needed to contribute energy requirement of the giant oocyte during oogenesis and later during embryogenesis.…”