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Neurogenetics

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by bilateral vestibular schwannomas and meningiomas. The recently isolated NF2 tumor suppressor gene encodes a 595 amino acid protein (merlin). Based on its homology to the moesin-ezrin-radixin family, merlin has been supposed to be linked to the plasma membrane, but its intracellular localization in cells physiologically expressing NF2 protein is still unknown.
In order to investigate the cellular localization of merlin, we used a monoclonal antibody directed against the N-terminal amino acids 1 - 168 (Transduction Laboratories). Fibroblasts were cultivated in RPMI and used in the 4th to 7th passages. In Western blotting experiments, the NF2 protein was highly expressed in human fibroblasts and detected by a single band of about 75kD. Immunofluorescent labelling and examination by confocal laser scanning microscopy revealed a marked staining on the central part or the entire cell body, in areas of spreading membranes and in filopodia. In addition, intense labelling was also found near the cell membrane of spontaneously apoptotic cells, as revealed by double labelling with anti-NF2 and in situ 3'end labelling of DNA double strand breaks. After preabsorption of the antibody with a N-terminal protein fragment (residues 1-265) of the NF2 protein, no immunoreactivity was found. Selective solubilization of the fibroblast membrane fraction using first Lubrol WX and then NP40 extraction, revealed a single band at 75 kD exclusively in the Lubrol WX fraction. In contrast, no band could be detected in the NP40 fraction.
In summary, merlin is concentrated in or linked to the plasma membrane and the localization in the spreading membranes may indicate a cell-substrate adhesion function.


Headings
Neurofibromatosis type 2 (NF2)
merlin

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