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BOR - Papers in Press, published online ahead of print January 18, 2006.
Biol Reprod 2006, 10.1095/biolreprod.105.047340
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BIOLOGY OF REPRODUCTION 74, 807–815 (2006)
DOI: 10.1095/biolreprod.105.047340
© 2006 by the Society for the Study of Reproduction, Inc.

Research Article

High Resolution Mapping of Ribosomal DNA in Early Mouse Embryos by Fluorescence In Situ Hybridization1

Lioudmila Romanova 3, Farida Korobova 3, Ekaterina Noniashvilli 4, Andrei Dyban 4, and Olga Zatsepina 2 3

Schemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS,3 Moscow 117997, Russia Institute of Experimental Medicine RAMN,4 St. Petersburg 197376, Russia

ABSTRACT

The nucleolar precursor bodies (NPBs) are numerous discrete entities present in the nuclei of early mammalian embryos, which structurally support active rRNA genes. However, whether all rRNA genes, including those not transcribed, are spatially associated with NPBs, and moreover what is the general arrangement of ribosomal DNA (rDNA) in early mouse embryos, still remain unanswered questions. In our study, we examined the localization of rDNA in transcriptionally silent (one-cell and early two-cell) and transcriptionally active (late two-cell) mouse embryos by highly sensitive fluorescence in situ hybridization with probes complementary to mouse rDNA repeats. The results obtained showed that irrespective of the rDNA transcriptional status, one or more NPBs per nucleus were not structurally associated with rDNA. These observations support the idea that NPBs are heterogeneous in their ability to recruit rRNA genes and thus to participate in reassembly of the mature nucleolus. As in somatic cells, and despite the absence of the characteristic nucleoli, the general arrangement of rRNA genes in early mouse embryos reflected the intensity of rDNA transcription. Ribosomal RNA genes were unequally distributed with respect to repeat putative copy numbers between nucleolar organizing region (NOR)-bearing chromosomes at the first cleavage division, and more strikingly, between sister chromatid NORs of a single nucleolar organizing chromosome. The latter indicates that sister chromatids might harbor various numbers of rRNA gene copies, and that the genes might be unequally distributed between the two blastomeres during the first cleavage mitosis.

early development, embryo, gene regulation

FOOTNOTES

1 Supported by the Russian Scientific Foundation for Basic Researches (projects 02-04-49373, 03-04-48951, and 06-04-49392).

2 Correspondence: Olga Zatsepina, Schemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS, Miklukho-Maklaya 16/10, Moscow, Russia 117997. FAX: 7 095 335 71 03; zatsepin{at}ibch.ru






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Copyright © 2006 by the Society for the Study of Reproduction.