Ribosomal RNA gene expression and chromosome aberrations in bovine oocytes and preimplantation embryos

This review focuses on the key features of development of the bovine oocyte and embryo, with comparisons of the developmental characteristics of embryos produced in vivo and in vitro. The oocyte is transcriptionally quiescent in the primordial and primary follicle. In the secondary follicle transcription is initiated in the oocyte and a ribosome-synthesizing nucleolus is established in this cell. Transcription and nucleolar activity are enhanced in the tertiary follicle during oocyte growth. When the oocyte reaches approximately 110 microm in diameter, corresponding to a follicle of about 3 mm in diameter, transcription ceases and the nucleolus is inactivated, forming a dense spherical remnant. During the final phase of follicular dominance this remnant becomes vacuolated and, in conjunction with resumption of meiosis, it disperses. The rRNA genes are apparently re-activated during the four-cell stage, that is, the third cell cycle after fertilization, but a nucleolus is not formed. During the subsequent cell cycle, that is, during the eight-cell stage, ribosome-synthesizing nucleoli are again established. Bovine embryos produced in vitro apparently display the same pattern of nucleolus development as that in embryos developed in vivo. Examination of the ploidy of embryonic cells using fluorescence in situ hybridization has revealed that the production of bovine embryos in vitro is associated with increased chromosome aberrations in the embryos. Blastocysts produced in vitro display a significantly higher rate of mixoploidy, that is, when the embryo consists of both normal diploid and abnormal polyploid cells, than that in embryos developed in vivo. The rate of mixoploidy among embryos produced in vitro increases with increasing developmental stage. Moreover, after fertilization in vitro, initially there is a high rate of 'true' polyploidy, that is, when all cells of the embryos are polyploid. However, the polyploid embryos are eliminated before they cleave beyond the eight-cell stage, the stage at which major activation of the embryonic genome occurs in cattle.

This article has been cited by other articles:

				M. Assidi, I. Dufort, A. Ali, M. Hamel, O. Algriany, S. Dielemann, and M.-A. Sirard Identification of Potential Markers of Oocyte Competence Expressed in Bovine Cumulus Cells Matured with Follicle-Stimulating Hormone and/or Phorbol Myristate Acetate In Vitro Biol Reprod, August 1, 2008; 79(2): 209 - 222. [Abstract] [Full Text] [PDF]

				H. Torner, N. Ghanem, C. Ambros, M. Holker, W. Tomek, C. Phatsara, H. Alm, M.-A. Sirard, W. Kanitz, K. Schellander, et al. Molecular and subcellular characterisation of oocytes screened for their developmental competence based on glucose-6-phosphate dehydrogenase activity Reproduction, February 1, 2008; 135(2): 197 - 212. [Abstract] [Full Text] [PDF]

				S. Ogushi, C. Palmieri, H. Fulka, M. Saitou, T. Miyano, and J. Fulka Jr. The Maternal Nucleolus Is Essential for Early Embryonic Development in Mammals Science, February 1, 2008; 319(5863): 613 - 616. [Abstract] [Full Text] [PDF]

				L. Vandaele, B. Mateusen, D. G D Maes, A. de Kruif, and A. Van Soom Temporal detection of caspase-3 and -7 in bovine in vitro produced embryos of different developmental capacity Reproduction, April 1, 2007; 133(4): 709 - 718. [Abstract] [Full Text] [PDF]

				A. S. Lequarre, J. M Traverso, J. Marchandise, and I. Donnay Poly(A) RNA Is Reduced by Half During Bovine Oocyte Maturation but Increases when Meiotic Arrest Is Maintained with CDK Inhibitors Biol Reprod, August 1, 2004; 71(2): 425 - 431. [Abstract] [Full Text] [PDF]

				V. Baran, A. Pavlok, B. Bjerregaard, C. Wrenzycki, D. Hermann, V. V. Philimonenko, G. Lapathitis, P. Hozak, H. Niemann, and J. Motlik Immunolocalization of Upstream Binding Factor and Pocket Protein p130 During Final Stages of Bovine Oocyte Growth Biol Reprod, April 1, 2004; 70(4): 877 - 886. [Abstract] [Full Text] [PDF]

				R. Dalbies-Tran and P. Mermillod Use of Heterologous Complementary DNA Array Screening to Analyze Bovine Oocyte Transcriptome and Its Evolution During In Vitro Maturation Biol Reprod, January 1, 2003; 68(1): 252 - 261. [Abstract] [Full Text] [PDF]