Centrosomal deployment of γ-tubulin and pericentrin: Evidence for a microtubule-nucleating domain and a minus-end docking domain in certain mouse epithelial cells

Abstract

This report provides evidence for two functionally and spatially distinct centrosomal domains in certain mouse cochlear epithelial cells. The vast majority of microtubules elongate from sites associated with the apical cell surface in these cells rather than from pericentriolar material surrounding the immediate environs of their apically situated centrioles. The distribution of g-tubulin and pericentrin at cell apices has been examined while microtubule nucleation is progressing because these centrosomal proteins are believed to be essential for microtubule nucleation.Antibodies to both proteins bind to pericentriolar regions but no binding has been detected at the apical cell surface-associated sites where the ends of thousands of recently nucleated microtubules are concentrated. Sparse transient microtubule populations can be detected between pericentriolar regions and surface sites while microtubule assembly advances. A procedure apparently operates in which the pericentriolar region functions as a microtubule-nucleating domain and the cell surface-associated sites operate as docking domains which capture the minus ends of microtubules that migrate to them shortly after nucleation.Docking domains may include some components of the pericentriolar material that have been relocated at the cell apex. A docking element hypothesis for centrosomal control of minus end positioning and dynamics in animal cells generally is proposed.This investigation has also shown that the concentration of g-tubulin and pericentrin around centrioles differs spatially and quantitatively in ways that are characteristic for the four cell types studied. Some of these characteristics can be

Measuring tubulin content in Toxoplasma gondii : A comparison of laser-scanning confocal and wide-field fluorescence microscopy

“…Second, endogenous ␣-tubulin itself may be used to a different extent in different organelles. T. gondii, similar to most eukaryotes, has multiple tubulins (including ␣, ␤, and ␥ isoforms), and it is clear from other organisms that the different tubulin isoforms are not used equally for all purposes (37)(38)(39)(40).…”

The centrosome is a dynamic structure that ejects PCM flares

“…movies available at jcs.biologists.org/supplemental. centrosomes with anti-Pericentrin antibodies (Mogensen et al, 1997).…”

Microtubule nucleation and anchoring at the centrosome are independent processes linked by ninein function

“…Protein complexes participating in microtubule nucleation have been extensively studied . By contrast, microtubule-anchoring complexes have been less well characterized (Bornens, 2002;Dammermann and Merdes, 2002;Mogensen, 1999;Mogensen et al, 1997;Mogensen et al, 2000;Quintyne et al, 1999).…”

“…However, in mammalian cells, γ-tubulin is localized to and nucleates microtubules at the two centrioles, whereas microtubule anchoring seems to be specific to the mother centriole . Furthermore, in polarized epithelial cells, microtubule-nucleation and -anchoring activities are taking place in distinct locations (Mogensen et al, 1997): γ-tubulin is concentrated at the centrosome, yet most microtubules are anchored at non-centrosomal apical sites, where, instead, ninein and centriolin accumulate. These results indicate that γ-tubulin might not be the sole factor dictating microtubule anchorage.…”