Regulation of microtubule dynamics and nucleation during polarization in MDCK II cells.

Abstract

Abstract. MDCK cells form a polarized epithelium when they reach confluence in tissue culture. We have previously shown that concomitantly with the establishment of intercellular junctions, centrioles separate and microtubules lose their radial organization (Bacallao, R., C. Antony, C. Dotti, E. Karsenti, E. H. K. Stelzer, and K. Simons. 1989. J. Cell Biol. 109:2817-2832. Buendia, B., M. H. Brt, G. Griffiths, and E. Karsenti. 1990Karsenti. . 110:1123Karsenti. -1136. In this work, we have examined the pattern of microtubule nucleation before and after the establishment of intercellular contacts. We analyzed the elongation rate and stability of microtubules in single and confluent cells. This was achieved by microinjection of Paramecium axonemal tubulin and detection of the newly incorporated subunits by an antibody directed specifically against the Paramecium axonemal tubulin. The determination of newly nucleated microtubule localization has been made possible by the use of advanced doubleimmunofluorescence confocal microscopy. We have shown that in single cells, newly nucleated microtubules originate from several sites concentrated in a region localized close to the nucleus and not from a single spot that could correspond to a pair of centrioles. In confluent cells, newly nucleated microtubules were still more dispersed. The microtubule elongation rate of individual microtubules was not different in single and confluent cells (4/xm/min). However, in confluent cells, the population of long lived microtubules was strongly increased. In single or subconfluent cells most microtubules showed a tla of < 30 min, whereas in confluent monolayers, a large population of microtubules had a t~a of >2 h. These results, together with previous observations cited above, indicate that during the establishment of polarity in MDCK cells, microtubule reorganization involves both a relocalization of microtubule-nucleating activity and increased microtubule stabilization.

MTCL1 crosslinks and stabilizes non-centrosomal microtubules on the Golgi membrane

“…8a) 15 . Given that MTs in polarized epithelial cells are stabilized compared with less differentiated cells 20,21 , these results further suggest that the N-terminal region may not require the KR-rich region to function in epithelial cells. Recently, the MT minusend-binding proteins, CAMSAPs, have been reported to exert a strong stabilizing effect on non-centrosomal MTs in epithelial cells [22][23][24] .…”

Molecular Aspects of Membrane Trafficking in Paramecium

“…Due to its preference for" + ---+ -" transport, it may be involved in trichocyst docking. Remarkably, such"+ ---+ -" directed transport to the cell periphery, as established for trichocysts (Plattner et al, 1982;Glas-Albrecht et al, 1991), has also been found in epithelia (Bacallao et al, 1989;Bre et al, 1990). Table I summarizes the relevant molecular details known so far from Paramecium.…”

Development and Cell Polarity of the C. elegans Intestine

“…By contrast, in many other epithelial cells most MTs are noncentrosomal and align along the apicobasal polarity axis. They create asymmetry by orienting their minus-and plus-ends towards the apical and basal membrane domains, respectively (Bacallao et al, 1989;Bre et al, 1990).…”