Over-expression of betaI tubulin in MDCK cells and incorporation of exogenous betaI tubulin into microtubules interferes with adhesion and spreading

Regional differences in expression of β-tubulin isoforms in schizophrenia

A growing body of evidence suggests that abnormal elements of the cytoskeleton may be associated with the pathophysiology of schizophrenia. Isoforms of a major cytoskeleton protein, β-tubulin, were recently demonstrated to have distinct roles in neuronal differentiation and cell viability. For these reasons, we tested the hypothesis that there are differences in the expression of β-tubulin isoforms (βI-βIV) in the brain in schizophrenia, using western blot analysis in an elderly group of subjects with this illness and a control group. We found that βI-tubulin protein expression was decreased in the anterior cingulate cortex and increased in the dorsolateral prefrontal cortex, but not changed in superior temporal gyrus or hippocampus in schizophrenia. Our data supports the growing body of evidence suggesting abnormalities of the cytoskeleton in schizophrenia.

The beta isotypes of tubulin in neuronal differentiation

The differences among the vertebrate beta isotypes of tubulin are highly conserved in evolution, suggesting that they have functional significance. To address this, we have used differentiating neuroblastoma cells as a model system. These cells express the betaI, betaII, and betaIII isotypes. Although there is no difference prior to differentiation, a striking difference is seen after differentiation. Both betaI and betaIII occur in cell bodies and neurites, while betaII occurs mostly in neurites. Knocking down betaI causes a large decrease in cell viability while silencing betaII and betaIII does not. Knocking down betaII causes a large decrease in neurite outgrowth without affecting viability. Knocking down betaIII has little effect on neurite outgrowth and only decreases viability if cells are treated with glutamate and glycine, a combination known to generate free radicals and reactive oxygen species. It appears, therefore, that betaI is required for cell viability, betaII for neurite outgrowth and betaIII for protection against free radicals and reactive oxygen species.

Potassium Channels Lost During Harvesting of Epithelial Cells are Restored with a Kinetics that Depends on Channel Species

The polarized distribution of K(+) channels in MDCK cells is lost upon harvesting and restored upon re-seeding. Using semi-quantitative PCR, in the present work we find that (i) Cells do not "wait" for the normal recycling of membrane proteins to restore their lost channels, but trigger their replacement, suggesting that the membrane has a way of engaging the nucleus. (ii) Replacement channels do not come from an internal reservoir, as it is the case with Na(+), K(+)-ATPase, but requires a de novo synthesis. (iii) Replacement is not an all-or-none response, since mRNA for MaxiK channels increases by 8-fold after re-seeding, but those for Kv1.6 and Kv1.7 are not affected by harvesting/re-seeding. (iv) TEA, charybdotoxin and iberiotoxin fail to trigger the replacement response in mature monolayers, suggesting that replacement is not due to suppression of channel function. (v) MDCK cells have a typical transporting epithelial phenotype (TEP) consisting of tight junctions (TJs) plus polarity. Although the polarized distribution of K-channels is a prominent attribute of TEP, blocking their function does not perturb the development of TEP, as gauged through the development of TJs, nor level of expression (Western blot) and distribution (confocal microscopy) of occludin, and claudins 1, 3 and 7.

Zebrafish beta tubulin 1 expression is limited to the nervous system throughout development, and in the adult brain is restricted to a subset of proliferative regions

Tubulin, the building block of microtubules, consists of an alpha and beta subunit, each in itself a family of several highly homologous isotypes. Abundance, tissue specificity, developmental regulation, and possibly function vary between isotypes. Six isotypes of beta tubulin (class I to class VI) have been cloned from several vertebrate species. Class I beta tubulin is believed to be widely expressed, but has not been studied by in situ hybridization in any vertebrate species so far. We have cloned a beta tubulin from zebrafish that appears most similar to other vertebrate class I tubulins and name it zbeta1 tubulin, accordingly. We report a distinct expression pattern of zbeta1 tubulin in the zebrafish embryo in restricted regions of the peripheral and central nervous system that comprise early-differentiating neurons. The expression pattern changes during development and in the adult zebrafish expression mostly is confined to a subset of proliferative zones that include the subependymal zone around the telencephalic ventricle, zones in the preoptic and hypothalamic area and in the olfactory epithelium. Thus, zbeta1 tubulin is expressed with remarkable selectivity during neuronal differentiation and neurogenesis in the embryonic and adult nervous system, respectively.

Association of the Ste20-like kinase (SLK) with the microtubule. Role in Rac1-mediated regulation of actin dynamics during cell adhesion and spreading

Cytoskeletal remodeling events are tightly regulated by signal transduction systems that impinge on adhesion components and modulators of cellular architecture. We have previously shown that the Ste20-like kinase (SLK) can induce apoptosis through the induction of actin disassembly and cellular retraction (Sabourin, L. A., Tamai, K., Seale, P., Wagner, J., and Rudnicki, M. A. (2000) Mol. Cell. Biol. 20, 684-696). Using immunofluorescence studies, we report that SLK is redistributed with adhesion components at large podosome-like adhesion sites in fibronectin-stimulated fibroblasts. However, in vitro kinase assays demonstrate that its activity is not modulated following fibronectin stimulation. Double immunofluorescence studies in exponentially growing or spreading fibroblasts show that SLK is associated with the microtubule network and can be coprecipitated with alpha-tubulin. Furthermore, the stimulation of adhesion site formation by microtubule-disrupting agents induces the relocalization of SLK with unpolymerized alpha-tubulin to large vinculin-containing adhesion complexes. Using microinjection studies, we show that ectopic expression of activated SLK induces the disassembly of actin stress fibers, a process that can be inhibited by dominant negative Rac1. Significantly, endogenous SLK can be colocalized with Rac1 in spreading cells on FN. Finally, the overexpression of SLK by adenoviral infection inhibits cell spreading on fibronectin. These results suggest that SLK is part of a microtubule-associated complex that is targeted to adhesion sites and implicated in the regulation of cytoskeletal dynamics.