Cytoplasmic gels

NOSSAL In Vitro Polymerization of Complex Cytoplasmic Gels... 

The work that follows pertains primarily to actin networks. Many proteins within a cell are known to associate with actin. Among these are molecules which can initiate or terminate polymerization, intercalate with and cut chains, crosslink or bundle filaments, or induce network contraction (i.e., myosin) (A,11,12). The central concern of this paper is an exploration of the way that such molecular species interact to form complex networks. Ultimately we wish to elucidate the biophysical linkages between molecular properties and cellular function (like locomotion and shape differentiation) in which cytoskeletal structures are essential attributes. Here, however, we examine the iri vitro formation of cytoplasmic gels, with an emphasis on delineating quantitative assays for network constituents. Specific attention is given to gel volume assays, determinations of gelation times, and elasticity measurements. 

Galiyas F. A cytoplasmic gel network capable of mediating the conversion of chemical energy to mechanical work in diverse cell processes A speculation. Acta Biol Hung. 61(4) (2010) 367-379. 

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

The specific resistance of the extracellular fluid is 2 to 200 fi cm. The ionic mobilities and specific resistance in the cytoplasm are of the same order of magnitude as those in the extracellular fluid, despite the gel-hke consistency commonly associated with the cytoplasm. 

Early descriptions of the changes in cytoplasmic structure that occurred during pseudopodia formation referred to a soluble (Sol) and a gelled or semisolid (Gel) state. Thus, it was assumed that the cytoplasm in the organelle-free peripheral cytoplasm was in the Sol state, whilst in pseudopodia (which resist deformation by mechanical forces) it is in the Gel state. Thus, the control of neutrophil functions via changes in cytoplasmic structure may be explained by understanding this so-called Sol —> Gel transition. It is perhaps more convenient to think of this transition as the processes that elongate and cross-link actin filaments. 

Until the past decade, the cytoplasm was widely considered to be structurally unorganized with the main division of labor at the organellar level. Certainly, relatively little was known about the nature of the cyto-skeleton (with the notable exception of the mitotic apparatus and striated muscle), and the dynamics of cytoplasmic behavior were conceptualized vaguely in terms of sol-gel transitions without a sound molecular foundation. Substantial improvements in electron, light, and fluorescence microscopy, as well as the isolation of discrete protein components of the cytoskeleton, have led the way to a much better appreciation of the structural organization of the cytoplasm. Indeed, the lacelike network of thin filaments, intermediate filaments, and microtubules in nonmuscle cells is as familiar today as the organelles identified... 

Subcellular structures (organelles) are present in the cell. Each one has its own characteristic activities and properties that work together to maintain the cell and its functions. The remainder of the cell is the gel-like cytoplasm, known as cytosol (Eigure 1.1). The largest organelle in the cell is the nucleus it contains the genetic... 

V/hen concentrated solutions of cytoplasmic extracts of certain cells are warmed to room temperature, the proteins form gels... 

Fig. 2 a) Results of gel fraction assay on cytoplasmic extracts of Ehrlich ascites cells (after Ishiura and 0kada(13)). 

Other nonhistone nuclear proteins. Polyacrylamide gel electrophoresis revealed more than 450 components in HeLa cell nuclei. Most are present in small amounts of <10,000 molecules per cell and are not detectable in cytoplasm.112 Among the more acidic proteins are many enzymes including RNA polymerases. There are also gene repressors, hormone-binding proteins, protein kinases, and topoi-somerases.113 Among the six most abundant nonhistone nuclear proteins in the rat are the cytoskeletal proteins myosin, actin, tubulin, and tropomyosin.114... 

Yin, H.L., and T.P. Stossel. 1979. Control of cytoplasmic actin gel-sol transformation by gelsolin, a calcium-dependent regulatory protein. Nature. 281 583-6. 

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