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General Comment |
LocusID: 64425.
Bjerregaard B, et al reported the Regulation of Ribosomal RNA Synthesis During the Final Phases of Porcine Oocyte Growth.
In porcine oocytes acquisition of meiotic competence coincides with a decrease of general tran-scriptional activity at the end of the oocyte growth phase and, specifically, of ribosomal RNA (rRNA) synthesis in the nucleolus. The present study investigated the regulation of rRNA synthesis during porcine oocyte growth. Localization and expression of components involved in regulation of the rRNA synthesis, (the RNA polymerase I-associated factor PAF53, upstream binding factor (UBF), and the pocket proteins p130 and pRb) were assessed by immunocytochemistry and semi-quantitative RT-PCR, and correlated with ultrastructural analysis and autoradiography following (3)H-uridine incubation in growing and fully grown porcine oocytes. In addition, meiotic resumption, ultrastructure, and expression of p130, UBF and PAF53 were analyzed in growing and fully grown porcine oocytes cultured with 100 micro M butyrolactone I (BL-I), a potent inhibitor of cyclin dependent kinases (cdk), to gain insight into the regulation of rRNA transcription during meiotic arrest. Immunocytochemical analysis demonstrated that p130 became co-localized with UBF and PAF53, and that the intensity of the PAF53 labeling decreased towards the end of the oocyte growth phase. These data suggest that the decrease in rRNA synthesis is regulated by inhibition of UBF by p130 as well as by decreased availability of PAF53. Moreover, expression of mRNA encoding PAF53 was decreased at the end of the oocyte growth phase. At the morphological level these events coin-cided with inactivation of the nucleolus as visualized by the transformation of the fibrillo-granular nucleolus to an electron-dense fibrillar sphere with remnants of the fibrillar centers at the surface. Meiotic inhibition with 100 micro M BL-I had a detrimental effect on the ability of porcine oocytes to resume meiosis, and on nucleolus morphology resulting in lack of RNA synthetic capability as the fibrillar components, where rRNA transcription and initial processing occur, condensed or even disintegrated.
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Re-localization of nuclear DNA helicase II during the growth period of bovine oocytes Baran V, et al .
Nuclear DNA helicase II (NDH II) is the bovine homolog of human RNA helicase A. The aim of this study was to compare NDH II localization between somatic cells (bovine embryonal fibroblasts) and female germ cells (oocytes), with the main focus on the dynamic changes in the redistribution of NDH II during the growth phase of the bovine oocytes. The fine granular staining of NDH II was spread in the whole nucleoplasm of fibroblasts, excluding the reticulated nucleoli. In contrast, the large reticulated nucleoli of the growing oocytes isolated from early antral follicles exhibited strong positivity for NDH II together with the immunostaining signals of upstream binding factor (UBF) and RNA polymerase I subunit (PAF53), documenting the high synthetic activity of these nucleoli. At the time of termination of oocyte growth, NDH II was preferentially located at the nucleolar periphery together with proteins of fibrillar centres. In fully grown oocytes, NDH II was still present in the thin periphery shell around the compact nucleolar core. The semiquantitative RT-PCR revealed that the average signal of NDH II mRNA in fully grown oocytes was only at 40% level in comparison with growing oocytes. Western blot analysis further confirmed that a 140 kD NDH II protein was abundant in growing oocytes, while the signal was substantially weaker in fully grown oocytes. The significant decrease in NDH II gene expression and in NDH II mRNA translation correlates with a termination of the oocyte growth. Altogether, the results demonstrate that NDH II expression parallels the activity of ribosomal RNA biosynthesis in the bovine growing oocytes.
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