[Microtubule dynamics in epithelial cells].
Microtubules (MTs) are necessary components of all eukaryotic cells. They fulfill various functions being involved in cell division, ciliar and flagellar beating, cell shape maintaining, organelle distribution in the cell, organization of other cytoskeletal elements. Dynamic features of MTs have been commonly studied in vitro or on undiffirentiated cultured cells by means of molecular and ultrastructural methods. It is generally accepted that the phenomenon of dynamic instability is the major mechanism of MT turnover in the cell. MTs radiate from the centrosome and take part in the distribution of cell organelles. In addition, epithelial, nerve, and skeletal muscle cells contain non-centrosomal MTs. A few hypothesis of their origin have been so far put forward. According to the capture-release hypothesis, MTs are first nucleated on the a centrosome, then release to be driven in various parts of the cell by molecular motors. Some alternative mechanisms of non-centrosomal MT formation are also proposed in literature. For example, the nucleation sites were reported not only in centrosomes but also in other parts of cells, such as the apical membranes of epithelial cells, the nuclear membrane of muscle cells, pigment granule aggregates of melanophores. On studying frog urinary bladder and large intestine epithelial cells the authors observed in these cells numerous non-centrosomal MTs. This makes epithelial cells, good models for analysing structural and dynamic features of non-centrosomal MTs in differentiated cells. For the urinary bladder the pool of specific granules may serve as MT organizing centers. Non-cenrosomal MTs of these cells have big diameters (35-38 nm) and form bundles oriented in the apical-basal axis of the cell. In addition, non-centrosomal MTs of these cells may participate in the transport of specific granules and giant vacuoles that appear under stimulated water flows through the cell.
Snigirevskaia
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ES
Institute of Cytology RAS, St. Petersburg. snigir@mail.cytspb.rssi.ru
Komissarchik
Ia Iu
IaIu
D000818:Animals; D001001:Anura; D002455:Cell Division; D002462:Cell Membrane / Q000502:physiology; D018385:Centrosome / Q000502:physiology; D002923:Cilia / Q000502:physiology; D003594:Cytoplasmic Granules / Q000502:physiology / Q000648:ultrastructure; D004847:Epithelial Cells / Q000502:physiology* / Q000648:ultrastructure; D005407:Flagella / Q000502:physiology; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D015388:Organelles / Q000502:physiology; D001743:Urinary Bladder / Q000648:ultrastructure