Adhesion Molecules-28

Advances and Experimental-2

Aging-9

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Channels and Transporters-79

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Circadian Rhythms-13

Coagulation-14

Cytokines/Growth Factors-52

Development-223

DNA-56

DNA Surveillance and Repair-42

Drug Design-17

Endocrine-66

Evolution-33

Extracellular Matrix-30

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Gene Expression-178

Gene Therapy-53

Heart-61

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Immunology-93

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Protein-12

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RNA-152

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Transplant-51

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Chapter category: Reproductive Biology

Nucleolar Remodeling in Nuclear Transfer Embryos

Chapter authors:
Jozef Laurincik and Poul Maddox-Hyttel

Transcription of the ribosomal RNA (rRNA) genes occurs in the nucleolus and results in ribosome biogenesis. The rRNA gene activation and the associated nucleolus forma- tion may be used as a marker for the activation of the embryonic genome in mammalian embryos and, thus serve to evaluate the developmental potential of embryos originating from varied nuclear transfer protocols. In bovine in vivo developed embryos, functional ribosome-synthesizing nucleoli become structurally distinct toward the end of the 4th post-fertilization cell cycle. In embryonic cell nuclear transfer embryos, fully developed nucleoli are not apparent until the 5th cell cycle, whereas in somatic cell nuclear transfer embryos the functional nucleoli emerge already during the 3rd cell cycle. Intergeneric reconstructed embryos produced by the fusion of bovine differentiated somatic cell to a nonactivated ovine cytoplast fail to develop fully functional nucleoli. In bovine in vivo developed embryos, a range of important nucleolar proteins (e.g., topoisomerase I, upstream binding factor and RNA polymerase I, fibrillarin, nucleophosmin and nucleolin) become localized to the nucleolar anlage over several cell cycles. This relocation is completed toward the end of the 4th cell cycle. A substantial proportion of bovine embryos produced by nuclear transfer of embryonic or somatic cells to bovine ooplasts display aberrations in protein localization in one or more blastomers. This information is indicative of underlying aberrations in genomic reprogramming and may help to explain the abnormalities observed in a proportion of fetuses and offspring derived from nuclear transfer embryos.

Jozef Laurincik
Constantine the Philosopher University, Faculty of Natural Sciences

Poul Maddox-Hyttel
Department of Animal and Veterinary Basic Sciences, Royal Veterinary and Agricultural University

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