EFFECT OF ENUCLEATION ON PROTEIN-SYNTHESIS DURING MATURATION OF BOVINE OOCYTES IN-VITRO

The role of the nucleus in protein synthesis reprogramming during oocy te maturation was examined in immature or mature bovine oocytes, enucl eated at the germinal vesicle (GV) stage or the metaphase II (MII) sta ge. Cumulus-oocyte complexes (COCs) were denuded before or after matur ation in vitro. Denuded oocytes were (i) enucleated al the GV or MII s tage (after DNA staining and ultraviolet (UV) exposure), (ii) stained and exposed to UV but not enucleated, or (iii) used as controls. After treatment, oocytes were labelled for 4 h with S-35-methionine or were matured for 24 h before labelling. GV- or MII-karyoplasts and small p ortions of cytoplasm (cytoplasts), removed during enucleation, were al so labelled. Labelled oocytes, karyoplasts or cytoplasts were prepared for one-dimensional polyacrylamide gel electrophoresis. Incorporation of labelled methionine into oocyte protein was measured. Enucleation dd not affect protein synthesis reprogramming, but incorporation of S- 35-methionine in immature UV-stained oocytes was high-possibly due to nuclear repair mechanisms. Protein profiles of GV- and MII-karyoplasts differed from those of immature and mature oocytes. In conclusion, no rmal protein synthesis reprogramming in the cytoplasm can occur in the absence of the nucleus, and specific proteins are synthesized in the nuclear region.