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

Reproduction - Tập 122 Số 1 - Trang 21-30 - 2001
P. Hyttel1, Dorthe Viuff2, Trudee Fair3, Jozef Laurinčík4, PD Thomsen5, H. Callesen6, PL Vos7, Peter J.M. Hendriksen7, S.J. Dieleman7, K. Schellander8, U. Besenfelder9, T. Grève2
1Department of Anatomy and Physiology, Royal Veterinary and Agricultural University, Groennegaardsvej 7, 1870 Frederiksberg C, Denmark. [email protected]
2Department for Clinical Studies, Reproduction, Royal Veterinary and Agricultural University, Groennegaardsvej 7, 1870 Frederiksberg C, Denmark;
3Department of Animal Science and Production, Lyons Research Farm, University College Dublin, Ireland;
4Konstantin the Philosopher University and Research Institute of Animal Production, Nitra, Slovak Republic;
5Department of Anatomy and Physiology and
6Department of Animal Breeding and Genetics, Danish Institute of Agricultural Sciences, 8830 Tjele, Denmark
7Department of Farm Animal Health, Faculty of Veterinary Medicine, Yalelaan 7, 3584 CL Utrecht, The Netherlands
8University of Bonn, Faculty of Agriculture, Institute of Animal Breeding Science, Endenicher Allee 15, 53115 Bonn, Germany;
9IFA-TULLN, Department of Biotechnology in Animal Production, Konrad Lorenz Str. 20, 3430 TULLN, Austria

Tóm tắt

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.

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Reproduction

Tập 122 Số 1

21-30

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