Structural Organization of the Cytomatrix

Porter, Keith R.

doi:10.1007/978-1-4684-5311-9_2

Cited by 13 publications

(11 citation statements)

References 14 publications

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“…In this connection, Porter and coworkers examined the effects of low temperature, Mg 21 , and some chemical reagents including thyrotropin on the ultrastructure of the microtrabecular lattices in whole-mounted and cultured cells by CPD and high-voltage EM (Luby and Porter, 1980;Porter, 1978Porter, , 1987Westermark and Porter, 1982). According to their results, the exposure of cells to a cold medium at 48C disclosed the lattices as looser than normal, while the lattices in cells incubated with a Mg 21 -deprived buffer were abnormally coarse and open.…”

Section: Absence Of Changes Of Microtrabecular Lattices By Various Exmentioning

confidence: 99%

What we have learned and will learn from cell ultrastructure in embedment‐free section electron microscopy

Kondo

2008

Microscopy Res & Technique

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The limitations inherent in conventional electron microscopy (EM) using epoxy ultrathin sections for a clear recognition of biological entities having electron densities similar to or lower than that of epoxy resin have led to the development of embedment-free sectioning for EM. Embedment-free section EM is reliably performed using water-soluble polyethylene glycol (PEG) as a transient embedding medium, with subsequent de-embedment of PEG by immersion into water, followed by critical point-drying (CPD) of the embedment-free section. The present author has stressed that this approach clearly discloses structures whose contours and/or appearance are accordingly vague and/or fuzzy in conventional EM, but does not reveal any new structures. Based on embedment-free electron microscopy (PEG-EM), this article presents five major findings regarding strand- or microtrabecular lattices which have been clearly revealed to occur in the cytoplasmic matrix-an impossibility with conventional EM. These are (1) the appearance of lattices of different compactness in various cells and in intracellular domains of a given cell; (2) the faithful reproduction from an albumin solution in vitro of strand-lattices with correspondingly increasing compactness following increasing concentrations; (3) the appearance of more compact lattices from gelated gelatin than from solated gelatin at a given concentration in vitro; (4) the appearance of either greater or less lattice-compactness by hyper- or hypotonic pretreatments of cells; and (5) the appearance of certain intracellular proteins confined to the centripetal demilune-domain of centrifuged ganglion cells which is occupied with strand-lattices of a substantial compactness. From these findings, questions now arise as to the biological significance of the individual strand itself in the microtrabecular lattices in PEG-EM. In addition, it may be that the appearance of strand-lattices in a given biological domain represents the presence of soluble proteins; the lattice-compactness indicates the concentration of soluble proteins in the domain, and the aqueous cytoplasm is equivalent to the aqueous solution. Further, the appearance of two contiguous lattice domains exhibiting differing degrees of compactness in a given cell indicates that cytoplasmic proteins are solated in a domain with less compact lattices, whereas they are gelated in the other domain. These proposed interpretations need to be confirmed by further studies. If confirmed, the control mechanisms of the localization and movement of intracellular organelles could then be understood on the basis not only of information about the cytoskeletons but also of cell ultrastructure-related information on the concentration and sol-gel states of intracellular proteins. In addition, possible interpretations of the significance of strand-lattices in PEG-EM are also applicable to the nucleoplasm, especially extra-heterochromatin (euchromatin) areas. Finally, several potential uses/advantages of PEG-EM in the cell-ultrastructure have also been ...

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Section: Absence Of Changes Of Microtrabecular Lattices By Various Exmentioning

confidence: 99%

What we have learned and will learn from cell ultrastructure in embedment‐free section electron microscopy

Kondo

2008

Microscopy Res & Technique

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“…Even less clear to me is their cytoplasmic location because, as far as I have been able to determine, the study of these proteins is usually carried out using cell extracts. Porter (1986; see also the text). (B) image obtained by HVEM of a magnified region of the cytoplasm of these cells, displaying the 'microtrabecular lattice' (MTL).…”

Section: Scaffolds Adaptors and Signalling Proteinsmentioning

confidence: 95%

“…Wolosewick and Porter (1979) responded to, and attempted to counter these criticisms, in a paper whose title included the phrase 'artifact or reality? It has been almost 25 years since Porter's last scientific publication (Porter, 1986); in view of that, and John Heuser's question, it seemed appropriate to revisit the MTL, but this time from a different vantage point. It is important to realize that Porter was strictly a microscopist (and a superb one) whose evidence implied that the MTL was a rigid structure, lacking the dynamics at work in living cells.…”

Section: Introductionmentioning

confidence: 99%

“…He was referring to the proposition advanced by Keith Porter in the 1970s and 1980s that the fundamental structure of cytoplasm of eukaryotic cells is a highly branched, filamentous network that Porter called the microtrabecular lattice (MTL) that ramified throughout the cytoplasm and contained most of its formed elements and cytoplasmic proteins. The literature detailing Porter's views on the matter can be accessed through his last scientific publication (Porter, 1986) and other papers in the book in which it appeared (Welch and Clegg, 1986). These and other features of the MTL are shown in Figure 1, assembled from photomicrographs that Porter sent to me in 1987.…”

Section: Introductionmentioning

confidence: 99%

“…Instead, the prevailing view then (and now) is that eukaryotic cell cytoplasm is composed of various organelles and other formed elements more or less suspended in an aqueous phase crowded with freely diffusing proteins and other macromolecules, metabolites and inorganic ions in what is usually referred to as the 'cytosol', but more on that deceptively simple term shortly. It has been almost 25 years since Porter's last scientific publication (Porter, 1986); in view of that, and John Heuser's question, it seemed appropriate to revisit the MTL, but this time from a different vantage point.…”

Section: Introductionmentioning

confidence: 99%

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Revisiting the microtrabecular lattice

Clegg

2010

Cell Biology International

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The 'microtrabecular lattice' (MTL) that Keith Porter described in the 1970s and 1980s is reconsidered as a proposed fundamental cytoplasmic structure of eukaryotic cells. Although considered to be an artefact by most cell biologists of his time (and probably ours), the case is made that something like the MTL may well exist, but in a much more dynamic form than images from electron microscopy imply and convey.

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Glycogen metabolism in cultured chick hepatocytes: A morphological study

et al. 1990

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Ultrastructural and autoradiographic observations of cultured chick hepatocytes under the following conditions are described: Induction of glycogen synthesis with glucose alone and glucose plus insulin, and glucagon-induced glycogen breakdown. Profiles of hepatocytes cultured in medium containing 10 mM glucose showed typical cellular organelles and occasionally a few glycogen granules. After incubation of hepatocytes with 3H-glucose, silver grains were found over these sparse glycogen granules, indicating a low level of glycogen synthesis by a few cells. After addition of 75 mM glucose for 1 hr about 3% of the profiles of cells showed glycogen, and by 24 hr half of the hepatocytes had glycogen. Addition of insulin plus glucose induced glycogen synthesis in 82% of the cells after 6 hr, and by 24 hr almost every cellular profile showed glyocgen particles. Morphologically, glycogen accumulation was similar whether the cells were stimulated by high glucose or by glucose plus insulin: glycogen granules appeared in restricted regions of the cytoplasm, which were rich in smooth endoplasmic reticulum (SER), and peroxisomes were found close to the newly deposited glycogen particles. At maximum glycogen accumulation the association of SER and peroxisomes with glycogen was less obvious. Glycogenolysis induced by incubation of glycogen-rich hepatocytes with glucagon resulted in proliferation of SER in the glycogen regions of the cells. These observations are compatible with the concept of regions in the hepatocyte cytoplasm specialized for glycogen metabolism. Possible roles for SER and peroxisomes found near glycogen particles and other organelles in hepatic glycogen metabolism are discussed.Recently the well-established embryonic chicken hepatocyte culture system (Grieninger and Granick, 1978;Grieninger, 1983) was used to study the regulation of glycogen metabolism under precisely defined conditions. By culturing hepatocytes in a chemically defined medium (without serum) it was possible to evaluate the role of glucose and insulin in hepatic glycogenesis, to study the effects of glucagon on glycogen breakdown, and to observe the influence of insulin-like growth factors (Parkes and Grieninger, 1985;Parkes et al., 1986). These studies showed that addition of high concentrations of glucose to the culture medium caused rapid glycogen deposition, but the levels obtained never equaled maximal in vivo fed hepatic glycogen levels. It was concluded that glycogen synthesis in response to glucose is driven primarily by mass action (i.e., the effect of increasing substrate concentration). In contrast, insulin added to the culture medium with glucose causes the restoration of physiological maximal levels of glycogen. Thus insulin was proposed as the major regulator of glycogen synthesis in the hepatocyte. No major differences were observed between insulin and insulin-like growth factors with respect to glycogen deposition. The addition of glucagon to the 0 1990 WILEY-LISS, INC. culture medium caused a rapid breakdown of glyco...

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Structural Organization of the Cytomatrix

Cited by 13 publications

References 14 publications

What we have learned and will learn from cell ultrastructure in embedment‐free section electron microscopy

What we have learned and will learn from cell ultrastructure in embedment‐free section electron microscopy

Revisiting the microtrabecular lattice

Glycogen metabolism in cultured chick hepatocytes: A morphological study

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