Effects of proteasome inhibitors on the nucleolar size of porcine oocytes

Abstract

During the final stage of oocyte growth, the morphology of the oocyte nucleoli changes into a compact structure. The objective of this study was to determine the involvement of the proteasome, which is a large protein complex responsible for degrading intracellular proteins, in the nucleolar compaction. The mean nucleolar diameter of growing porcine oocytes (about 100 μm in diameter) was larger than that of fully grown (120 μm) oocytes (15.5 ± 0.3 vs. 13.2 ± 0.1 μm, P<0.05). When fully grown oocytes were treated with proteasome inhibitors, MG132 (10 and 20 μM) and lactacystin (100 and 200 μM), the nucleolar diameter significantly increased from 12.9 μm to 14.9-16.1 μm. In contrast, transcription inhibitors, actinomycin D (0.8-8 μM) and α-amanitin (10-100 μM) reduced the nucleolar diameter of growing oocytes to 9.4-12.4 μm. MG132 partially prevented this reduction in nucleolar diameter. These results suggest that the proteasome regulates the nucleolar size in porcine oocytes perhaps through the degradation of nucleolar proteins. © 2012 by the Society for Reproduction and Development.