Cell Biology

Reversible Disassembly

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Science  07 Mar 2003:
Vol. 299, Issue 5612, pp. 1487
DOI: 10.1126/science.299.5612.1487d

In animal cloning, nuclei from somatic cells are transplanted into recipient eggs, and the cytoplasm of the egg reprograms the differentiated nucleus so that early development can begin. One stage in this process is the disassembly of the nucleoli—the sites at which ribosomes are assembled—in the donor nucleus. Xenopus eggs do not synthesize ribosomal RNA and do not possess nucleoli, which reappear when the embryo reaches the blastula stage. Using Xenopus germ cell cytosol, Gonda et al. have characterized two proteins, FRGY2a and FRGY2b, which promote nucleolar disassembly when added to isolated somatic nuclei. These proteins were already known to act as transcription factors and to mask maternal messenger RNA in oocytes. Corroborating the role of the proteins in nucleolar dynamics, transfection of the C-terminal fragment of FRGY2a, which enters the nucleus freely and binds to nucleoli, triggered nucleolar disassembly in cells in culture. — SMH

Nature Cell Biol. 10.1038/ncb939 (2003).

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