In eukaryotic cells, two concentric membranes, the nuclear envelope (NE), separate the nucleus from the cytoplasm. The NE is punctured by nuclear pore complexes (NPCs; molecular mass 120 MDa) that serve as regulated pathways for macromolecules entering and leaving the nuclear compartment. Transport across NPCs occurs through central channels. Such import and export of macromolecules through individual NPCs can be elicited in the Xenopus laevis oocyte by injecting the mineralocorticoid aldosterone and can be visualized with atomic force microscopy. The electrical NE resistance in intact cell nuclei can be measured in parallel. Resistance increases when macromolecules are engaged with the NPC. This article describe six observations made from these experiments and the conclusions that can be drawn from them. (i) A homogeneous population of macromolecules (approx. 100 kDa) attaches to the cytoplasmic face of the NPC 2 min after aldosterone injection. They are most likely to be aldosterone receptors. After a few minutes, they have disappeared. (ii) Large plugs (approx. molecular mass 1 MDa) appear in the central channels 20 min after hormone injection. They are most likely to be ribonucleoproteins exiting the nucleus. (iii) Electrical resistance measurements in isolated nuclei reveal transient electrical NE resistance peaks: an early (2 min) peak and a late (20 min) peak. Electrical peaks reflect macromolecule interaction with the NPC. (iv) Spironolactone blocks both the early and late peaks. This indicates that classic aldosterone receptors are involved in the pregenomic (early) and post-genomic (late) responses. (v) Actinomycin D and, independently, RNase A block the late electrical peak, confirming that plugs are genomic in nature. (vi) Intracellular calcium chelation blocks both early and late electrical peaks. Thus, the release of calcium from internal stores, which is known to be the first intracellular signal in response to aldosterone, is a prerequisite for the late genomic response.
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February 2003
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Conference Article|
February 01 2003
Route of steroid-activated macromolecules through nuclear pores imaged with atomic force microscopy
H. Oberleithner;
H. Oberleithner
1
Institute of Physiology, University of Münster, Robert-Koch Strasse 27a, D-48149 Münster, Germany
1To whom correspondence should be addressed (e-mail oberlei@uni-muenster.de).
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C. Schäfer;
C. Schäfer
Institute of Physiology, University of Münster, Robert-Koch Strasse 27a, D-48149 Münster, Germany
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V. Shahin;
V. Shahin
Institute of Physiology, University of Münster, Robert-Koch Strasse 27a, D-48149 Münster, Germany
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L. Albermann
L. Albermann
Institute of Physiology, University of Münster, Robert-Koch Strasse 27a, D-48149 Münster, Germany
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Publisher: Portland Press Ltd
Online ISSN: 1470-8752
Print ISSN: 0300-5127
Copyright 2003 Biochemical Society
2003
Biochem Soc Trans (2003) 31 (1): 71–75.
Citation
H. Oberleithner, C. Schäfer, V. Shahin, L. Albermann; Route of steroid-activated macromolecules through nuclear pores imaged with atomic force microscopy. Biochem Soc Trans 1 February 2003; 31 (1): 71–75. doi: https://doi.org/10.1042/bst0310071
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