The brush border of small intestinal enterocytes is highly enriched in cholesterol- and glycosphingolipid-containing membrane microdomains, commonly termed as lipid ‘rafts’. Functionally, transcytosis of IgA and exocytosis of newly made brush-border proteins in enterocytes occur through apical lipid raft-containing compartments, but little is otherwise known about these raft microdomains. We therefore studied in closer detail apical lipid-raft compartments in enterocytes by immunogold electron microscopy and biochemical analyses. Novel membrane structures, deep-apical tubules, were visualized by the non-permeable surface marker Ruthenium Red in the brush-border region of the cells. The surface-connected tubules were labelled by antibodies to caveolin-1 and the glycolipid asialo GM1, and they were sensitive to cholesterol depletion by methyl-β-cyclodextrin, indicating the presence of raft microdomains. Deep-apical tubules were positioned close to the actin rootlets of adjacent microvilli in the terminal web region, which had a diameter of 50–100 nm, and penetrated up to 1 μm into the cytoplasm. Markers for transcytosis, IgA and the polymeric immunoglobulin receptor, as well as the resident brush-border enzyme aminopeptidase N, were present in these deep-apical tubules. We propose that deep-apical tubules are a specialized lipid-raft microdomain in the brush-border region functioning as a hub in membrane trafficking at the brush border. In addition, the sensitivity to cholesterol depletion suggests that deep-apical tubules function as a cell-surface membrane reservoir for cholesterol and for rapid adaptive changes in the size of microvilli at the brush border.
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July 01 2003
Deep-apical tubules: dynamic lipid-raft microdomains in the brush-border region of enterocytes
Gert H. HANSEN
;
Gert H. HANSEN
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
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Jens PEDERSEN
;
Jens PEDERSEN
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
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Lise-Lotte NIELS-CHRISTIANSEN
;
Lise-Lotte NIELS-CHRISTIANSEN
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
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Lissi IMMERDAL
;
Lissi IMMERDAL
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
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E. Michael DANIELSEN
E. Michael DANIELSEN
2
Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
2To whom correspondence should be addressed (e-mail midan@imbg.ku.dk).
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Biochem J (2003) 373 (1): 125–132.
Article history
Received:
February 10 2003
Revision Received:
April 02 2003
Accepted:
April 10 2003
Accepted Manuscript online:
April 10 2003
Citation
Gert H. HANSEN, Jens PEDERSEN, Lise-Lotte NIELS-CHRISTIANSEN, Lissi IMMERDAL, E. Michael DANIELSEN; Deep-apical tubules: dynamic lipid-raft microdomains in the brush-border region of enterocytes. Biochem J 1 July 2003; 373 (1): 125–132. doi: https://doi.org/10.1042/bj20030235
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