Nuclear distribution of RNA polymerase II in human oocytes from antral follicles: Dynamics relative to the transcriptional state and association withsplicing factors

The intranuclear distribution of two (unphosphorylated and hyperphosphoryla ted) forms of RNA polymerase II (Pol II) was studied in human oocytes from antral follicles using immunogold labeling/electron microscopy. The distrib ution of Pol II was analyzed relative to the transcriptional state of the o ocyte as well as to the distribution of two splicing factors (snRNPs and SC -35) in the intranuclear entities, namely, interchromatin granule clusters (IGCs), nucleolus-like bodies (NLBs), and perichromatin fibrils (PFs). The results showed that (1) antibodies directed against two forms of Pol II hav e similar pattern of intranuclear distribution, (2) both Pal II and splicin g factors progressively accumulate in IGCs with decrease in the transcripti onal activity of the oocyte nucleus, (3) both Pol II and splicing factors l ocalize to PFs, and (4) Pol II is present in the NLBs at all transcriptiona l states of the oocyte nucleus. These studies confirm earlier proposals tha t PFs represent a nuclear domain in which RNA transcription/processing are spatially coupled. The accumulation of Pol II and splicing factors in IGCs concomitant with a decrease in the transcriptional activity suggests a coor dinated mechanism for the movement of both Pol II and splicing factors from the sites of action to the sites of storage, J. Cell. Biochem. 77:654-665, 2000. (C) 2000 Wiley-Liss, Inc.