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PubMed1979

The cytoskeleton and plasma membrane.

The major cytoskeletal elements (microfilaments, microtubules, and 10-nm filaments) are frequently found attached to or near the plasma membrane in arrays which can sometimes be shown experimentally to be related to cell form and movement. Ultrastructural investigations show that attachment is direct, by amorphous electron-dense material, by cell-cell junctions, or by cell-substrate attachment sites, but the chemistry of attachment is poorly understood. The structural and functional polarity of the attached elements has been defined for some microfilaments attached to plasma membrane, but this important parameter has been investigated only slightly for microtubules and not at all for 10-nm filaments attached to membranes. Assemblies of cytoskeletal elements and plasma membrane evidently are structurally stable enough to be observable by electron microscopy and to survive isolation by the usual biochemical techniques, but observations of living cells show that many assemblies of cytoskeleton and plasma membrane undergo rearrangement and interconversion. The biochemical basis and physiological meaning of many of these changes are poorly understood.

Actins↗
PubMed1979

The role of cytoskeleton in adreno-medullary secretion.

Chromaffin cells of the adrenal medulla contain prominent arrays of microtubules and microfilaments. One population of microtubules radiates from the cytocentrum and permeates the areas of the cytoplasm containing chromaffin granules; the other population of microtubules forms a subplasmalemmal network together with actin-like microfilaments. Hence, the cytoskeletal elements in chromaffin cells are strategically located to participate in the mobility of chromaffin granules to the cell surface and to regulate access of the granules to the plasma membrane during exocytosis. Agents which effect the integrity of the cytoskeleton clearly affect the secretory process in a manner which indicates that the microtubules and microfilaments play an active role in the release process.

Adrenal Medulla↗
PubMed1979

The role of cytoskeleton in neuron activity.

The extensive cytoskeleton present in brain tissue is composed of microfilaments, neurofilaments, and neurotubules. A clear understanding of each of these structures is required to accurately define their participation in neuronal functions. Until more is known, therefore, we are restricted to speculate on their importance to the general activity of the cell. The presence of microfilamentous proteins in nerve endings -- the sites where nerve transmission is chemically sustained -- strongly suggests their participation in the release of putative neurotransmitters, a hypothesis that may be substantiated in the near future. It follows that alteration in assembly, disassembly, or interaction among the various cytoskeletal components may permit some insight into the causes and origins of a variety of neurological alterations affecting humankind.

Animals↗
PubMed1977

Restoration of normal morphology, adhesion and cytoskeleton in transformed cells by addition of a transformation-sensitive surface protein.

Transformed cells lack a large, external, transformation-sensitive (LETS) glycoprotein which is a major surface component of their normal counterparts. Addition of LETS glycoprotein isolated from normal cells to transfomed cells restores certain morphological features and adhesive properties characteristic of normal cells. LETS protein is detected on the cell surface both by iodination using lactoperoxidase and by immunofluorescent staining. The surface distribution pattern detected by immunofluorescence is strikingly similar to that of normal cells. After addition of LETS protein, transformed cells also exhibit well defined actin cables which are not seen in untreated, transformed cells. All these alterations can be blocked by treating LETS protein with specific antisera or by subjecting it to mild trypsinization prior to addition to transformed cells. The effects are rapidly reversible by mild trypsinization, which removes the added LETS protein. The high rate of uptake of 2-deoxyglucose, characteristic of transformed cells, is not affected by LETS protein. These results suggest that LETS protein may have a role in cell attachment and spreading, and affect the organization of cytoskeleton.

Actins↗
PubMed1979

Keratin cytoskeletons in epithelial cells of internal organs.

An antiserum against human epidermal keratins was used to detect keratins in frozen sections of various rabbit and human tissues by indirect immunofluorescence. Strong staining was observed in all stratified squamous epithelia (epidermis, cornea, conjunctiva, tongue, esophagus, vagina, and anus), in epidermal appendages (hair follicle, sebaceous gland, ductal and myoepithelial cells of sweat glands), as well as in Hassall's corpuscles of the thymus, indicating that all contain abundant keratins. No staining by the antiserum was observed in fibroblasts, muscle of any type, cartilage, blood vessel, nerve tissue, iris or lens epithelium, or the glomerular or tubular cells of the kidney. In contrast, the antiserum stained the cells of most epithelia of the intestinal tract, urinary tract (urethra, bladder, ureter, collecting ducts of kidney), female genital tract (cervix, cervical glands, uterus, and oviduct), and respiratory tract (trachea and bronchi). Epithelial cells of the fine ductal system in the pancreas and submaxillary gland also stained well. When primary cultures of epithelial cells derived from bladder, intestine, kidney, and trachea were grown on glass coverslips and stained with anti-keratin, fiber networks similar to those of cultured keratinocytes were observed. These results show that keratins constitute a cytoskeleton in epithelial cells of diverse morphology and embryological origin. The stability of keratin filaments probably confers the structural strength necessary for cells covering a free surface. Keratin staining can be used to obtain information about the origin of cell lines.

Animals↗
PubMed1979

The outer boundary of the cytoskeleton: a lamina derived from plasma membrane proteins.

We prepared the cytoskeletal framework by gently extracting cells with Triton X-100. Lipids and soluble proteins were removed, leaving a complex meshlike structure which contains the cell nucleus and is composed of the major cell filament networks as well as the microtrabeculae with attached polyribosomes. The surface sheet or lamina covering this structure contains most of the cell surface proteins by the following criteria. Intact cells are labeled externally with radioiodine and then extracted with detergent. The iodinated poteins remain almost entirely with skeletal framework. A new major integral protein, the coat protein of Sindbis virus, is inserted into the plasma membrane of infected cells. This new protein is heavily iodinated and remains almost completely associated with the framework after extraction. Lectin binding and poliovirus binding sites are also retained after detergent extraction. Our results indicate that plasma membrane proteins form a sheet or lamina upon removal of lipids. This lamina reproduces even complex surface convolutions and appears to be supported by and intimately connected to the underlying skeleton. In this case, the surface lamina, and hence the plasma membrane of the original intact cell, might be viewed as a component of the cytoskeletal framework.

Animals↗
PubMed1979

Pinocytosis in L cells: its dependence on membrane sterol and the cytoskeleton.

Pinocytosis in L-cells, grown in serum-free medium, was depressed when cultures were treated with oxygenated derivatives of cholesterol which inhibited sterol synthesis and reduced the sterol concentration of the plasma membranes. Noninhibitory sterols, such as cholesterol or desmosterol counteracted the effects of the inhibitors. Treatment with polylysine increased the rate of pinocytosis in sterol-depleted cells to a level similar to the enhanced rate found in polylysine treated control cells. Drugs which interfere with cytoskeletal systems (microfilaments, microtubules) also depressed pinocytosis but their effect could not be overcome by treatment with polylysine.

Animals↗