Localization of tropomyosin in mouse embryo fibroblasts

The discovery of tau protein

In January of this year I received an unexpected request from George Bloom to contribute an historical perspective on "the discovery of tau protein," an event that occurred roughly 50 years ago. My first thought was that it could not have been that long ago, as the memories of what was my first independent scientific discovery are still fresh in my mind today. But 50 years is half a century and, as I thought about the events, I realized how much the practice of science has changed.

The cytoskeleton of chick retinal pigment epithelial cells in situ

Gelatin-coated slides were used to obtain en face preparations of retinal pigment epithelium (RPE) from 6- to 21-day-old chick embryos in order to study the distribution of F-actin in microfilaments (MF) and the MF-associated proteins, myosin, tropomyosin, alpha-actinin and vinculin in situ at different stages of development by fluorescence microscopy. The epithelial sheets were fixed in formaldehyde and then extracted in a solution containing 0.1% Triton X-100. NBD-Phallacidin was used to visualize the F-actin in MF, and antisera against myosin, tropomyosin, alpha-actinin and vinculin were used to determine the distribution of these four MF-associated proteins. F-actin, myosin, tropomyosin, alpha-actinin and vinculin were present in cortical rings around the apical ends of the RPE cells throughout this period of development. Of these proteins, only F-actin was identified in the apical processes of RPE cells. The increase in the amount of F-actin could be followed as the length and the number of apical processes increased with age and maturation of RPE cells. F-actin was first detected in numerous short apical processes on the surface of each RPE cell on day 12. From day 12 to day 17, they were at an intermediate stage of elongation and from day 17 onward all of the RPE cells had long F-actin-containing apical processes. These results indicate that the F-actin-containing MF assemble much later in the apical processes than in the cortical rings.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial cell monolayer integrity. I. Characterization of dense peripheral band of microfilaments

Although the endothelial cell (EC) cytoskeleton has been studied both in vitro and in vivo, little is known about its role in endothelial integrity. We have previously suggested that specific EC microfilament (MF) structure, which we have termed the "dense peripheral band (DPB)," may play a major role in this process. We have extended our studies to characterize this structure in pig aortic ECs in vitro. During the growth of EC cultures, the DPB appears only when the cultures have attained confluency. Using double fluorescent labeling, we found that alpha-actinin, myosin, and tropomyosin colocalized with the F-actin making up the DPB. Occasional microtubules were present in this region, although there was no preferred association between microtubules and the DPB. Colocalization studies revealed vinculin plaques at the cell-cell interface. Thin MFs extended from the DPB into the cytoplasmic side of these plaques. The DPB was completely disrupted by low dose cytochalasin B within 30 minutes, whereas many central MF bundles were still present at 24 hours. The results of this study suggest that the DPB is a distinct structure in the confluent EC monolayer and is closely associated with the ability of ECs to form and maintain the EC monolayer. The disruption of the DPB as an important initial event in the pathogenesis of vascular diseases such as atherosclerosis is discussed.

Microtubule-organizing centers and cell migration: effect of inhibition of migration and microtubule disruption in endothelial cells

We have previously shown that microtubule-organizing centers (MTOC's) become preferentially oriented towards the leading edge of migrating endothelial cells (EC's) at the margin of an experimentally induced wound made in a confluent EC monolayer. To learn more about the mechanism responsible for the reorientation of MTOC's and to determine whether a similar reorientation takes place when cell migration is inhibited, we incubated the wounded cultures with colcemid (C) and cytochalasin B (CB), which disrupt microtubules (MT's) and microfilaments (MF's), respectively. The results obtained showed that the MTOC reorientation can occur independent of cell migration since MTOC's reoriented preferentially toward the wound edge in the CB-treated cultures, even though forward migration of the EC was inhibited. In addition, the MTOC reorientation is inhibited by C, indicating that it requires an intact system of MT's and/or other intracellular structures whose distribution is dependent on that of MT's.

Localization of the neurofilament protein in neuroblastoma cells by immunofluorescent staining

Neurofilament protein (54,000-56,000 daltons) has been localized in murine neuroblastoma cells by indirect immunofluorescent staining with antisera to purified calf brain neurofilament protein. In some cells with only short processes, specific staining of fibrous material was present in the perinuclear region while in other cells similar fibers, coiled to varying degrees, were present in other regions of the cytoplasm. In cells with longer processes a stained fiber extended throughout each process. The staining pattern observed followed the distribution of bundles of 100 A filaments as determined by electron microscopy. The fibers did not stain with antisera to tubulin or tropomyosin. The observations reported strongly indicate (i) that neurofilament protein isolated from calf brain is antigenically related to a component of the bundles of 100 A filaments in neuroblastoma cells, and (ii) that the neurofilament protein is an integral part of bundles of 100 A filaments in neuroblastoma cells, while neither tubulin nor tropomyosin is present in these bundles.