Abstract
We describe novel nucleolar structures, observed by thin section electron microscopy in oocyte nuclei of the grashopperLocusta migratoria, which we interpret, based on morphological and compositional criteria, as rDNA transcription units. Morphologically they resemble the condensed and foreshortened “Christmas trees” seen in Miller spreads of nucleolar chromatin prepared from the same biological material. They contain DNA and rRNA as shown by immunocytochemistry and in situ hybridization and are concentrated in several intranucleolar cavities. The presumptive rDNA transcription units extend throughout the interior of these nucleolar pockets or are selectively enriched at their outermost zones in close contact with the surrounding fibrillarinpositive dense component. We suggest that the nucleolar pockets ofLocusta oocytes are equivalent to the fibrillar centers of somatic nucleoli and discuss possible implications for the current understanding of the functional organization of nucleoli.
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Edited by: S. A. Gerbi
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Scheer, U., Xia, B., Merkert, H. et al. Looking at christmas trees in the nucleolus. Chromosoma 105, 470–480 (1997). https://doi.org/10.1007/BF02510484
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DOI: https://doi.org/10.1007/BF02510484