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H Holtzer

Publications and source records attributed to H Holtzer.

At least 73 records · Page 4Linked to original sources
PubMed1981

Changes in the sulfated proteoglycans synthesized by "aging" chondrocytes. I. Dispersed cultured chondrocytes and in vivo cartilages.

Structural and chemical changes in the sulfated proteoglycans synthesized by "aging" cultures of dispersed chondrocytes were compared to those synthesized by freshly excised, intact cartilage explants in organ culture from chickens of various ages. In vitro, chondrocytes isolated from embryonic chick vertebral cartilages synthesized a proteoglycan monomer characteristic of cartilage (type IV). Monomers synthesized between 3 days and 6 weeks in culture: (i) showed a decrease in average molecular size, which could be correlated, in part, with a decrease in the average size of the chondroitin sulfate chains; (ii) were able to interact with hyaluronic acid to form proteoglycan aggregates regardless of size; (iii) maintained a relatively constant 6S/4S disaccharide ratio of 2.2 for chondroitin sulfate; and (iv) maintained a constant keratan sulfate composition of 5 to 10%. Sulfated proteoglycans synthesized by freshly excised embryonic tibia cartilaginous head and by tibial articular cartilages of 1- and 6-year-old chickens were compared. With age: (i) the type IV monomer size decreased; (ii) the chondroitin sulfate chain size decreased; (iii) the type IV monomers retained their ability to interact with hyaluronic acid; (iv) the 6S/4S disaccharide ratio decreased from 1.7 to 0.6; (v) the keratan sulfate composition increased from 7 to 40%. Although monomer sizes decrease in both the culture and explant systems, in other respects the differences are considerable. These findings suggest that the changes in sulfated proteoglycans observed in subcultured monolayers of chondrocytes must be interpreted with caution when attempting to relate them to the changes that occur in aging in vivo chondrocytes.

Animals↗
PubMed1981

Changes in the sulfated proteoglycans synthesized by "aging" chondrocytes. II. Organ-cultured vertebral columns.

Sulfated proteoglycans synthesized by intact embryonic chick vertebral cartilages maintained in organ culture were characterized by labeling the vertebral chondrocytes with [35S]sulfate. More than 95% of the sulfated macromolecules synthesized by the cartilages are retained in their extracellular matrix. Sucrose velocity sedimentation gradient analyses revealed that the intact cartilages synthesized primarily proteoglycan monomers typical of cartilage and also small amounts of a smaller sized proteoglycan. The continuously varying size distribution of monomers which characterize a population of proteoglycans, could, in part, be attributed to heterogeneity of other chondroitin sulfate chain size. Changes in the proteoglycans synthesized by intact cartilages were analyzed between 6 h and 8 days of organ culture: (i) monomers decreased in molecular size with age in organ culture; (ii) the decrease in monomer size could be partially attributed to a shortening of their chondroitin sulfate chains; (iii) the 6S/4S disaccharide composition of the chondroitin sulfate chains also changed with culture age, from 1.8 to 0.3. This change was shown to be independent of the concomitant decrease in monomer size. These changes are similar to those which occur in proteoglycans synthesized by articular cartilages from chickens of increasing age. This cartilage culture system is likely to be a more useful model for studying changes which accompany aging and/or senescence in cartilage in vivo than the more commonly studied dispersed chondrocyte cultures.

Animals↗
PubMed1981

Taxol induces postmitotic myoblasts to assemble interdigitating microtubule-myosin arrays that exclude actin filaments.

Taxol has the following effects on myogenic cultures: (a) it blocks cell replication of presumptive myoblasts and fibroblasts. (b) It induces the aggregation of microtubules into sheets or massive cables in presumptive myoblasts and fibroblasts, but not in postmitotic, mononucleated myoblasts. (c) It induces normally elongated postmitotic myoblasts to form stubby, star-shaped cells. (d) It reversibly blocks the fusion of the star-shaped myoblasts into multinucleated myotubes. (e) It augments the number of microtubules in postmitotic myoblasts, and these are assembled into interdigitating arrays of microtubules and myosin filaments. (f) Actin filaments are largely excluded from these interdigitating microtubule-myosin complexes. (g) The myosin filaments in the interdigitating microtubule-myosin arrays are aligned laterally, forming A-bands approximately 1.5 micrometers long.

Alkaloids↗
PubMed1981

Purification and characterization of a 43,000 dalton "DNAase binding protein" distinct from actin.

"DNase binding protein" of 43K daltons as determined by SDS-polyacrylamide gel electrophoresis, was purified from the 0.1 M KCl-soluble (non-structural) fraction of chicken skeletal muscle. The protein was distinct from actin in amino acid composition and physicochemical properties. "DNase binding protein" was also isolated from other kinds of muscle and non-muscle cells. The ratio of the amino acid incorporation rate of "DNAase binding protein" to that of actin is different skeletal and smooth muscle and non-muscle cells.

Actins↗
PubMed1980

Selective effects of phorbol 12-myristate 13-acetate on myofibrils and 10-nm filaments.

Phorbol 12-myristate 13-acetate (PMA) has a prompt and selective catabolic effect on striated myofibrils in postmitotic myotubes. Fluorescein-labeled antibodies against light meromyosin were used to follow the effects of PMA on the muscle-specific myosin in myofibrils. The response of actin filaments was monitored by decoration with heavy meromyosin. The response of the two types of 10-nm filaments in myotubes was followed by fluorescein- and rhodamine-labeled antibodies to the fibroblastic and muscle-specific filament proteins, respectively. Within 2-3 days, PMA induced dismantling of virtually every striated myofibril in every myotube in the culture. These myotubes bound little or no anti-light meromyosin, and tests to detect the alpha-actin filaments of the myofibrils with heavy meromyosin were negative. In contrast, the nonmuscle actin in the subsarcolemmal microfilaments persisted in PMA-treated myotubes and was decorated with heavy meromyosin. The sarcoplasmic reticulum, mitochondria, and Golgi bodies appeared normal. Myotubes depleted of myofibrils by PMA displayed large numbers of muscle-specific 10-nm filaments. This preferential degradation of the myosin and actin of the myofibrils were reversible. These myotubes formed a normal complement of myofibrils 24-48 hr after removal of PMA. When, after 3 days in PMA, the cultures were treated for an additional 3-8 days, a transitory subpopulation of PMA-resistant myotubes appeared.

Animals↗
PubMed1980

Effects of 12-O-tetradecanoylphorbol-13-acetate on the differentiation of avian melanocytes.

12-O-Tetradecanoylphorbol-13-acetate (TPA) has been reported to inhibit and/or delay the terminal differentiation of a variety of cell types. More recently, TPA has been reported to enhance melanogenesis in cultured human melanoma cells. This study focuses on the effect of TPA on the differentiation of normal avian melanocytes. TPA blocked melanogenesis in normal replicating presumptive melanoblasts, as well as in replicating pigmented melanocytes derived from the neural crest, the retinal pigment epithelium, and the pecten oculi. These normal embryonic cells not only failed to synthesize melanin but also failed to assemble premelanosomes and to assume either the characteristic dendritic processes of normal trunk melanocytes or the epithelioid morphology of the normal retinal pigment epithelial cell. This inhibition was remarkably reversible. Following removal of TPA, the previously blocked neural crest cells became pigmented and formed their characteristic dendritic processes, whereas the previously blocked retinal cells formed a pigmented epithelium. The effect of TPA on these normal cells was dependent on duration of exposure and degree of differentiation of the cells at the time of exposure. TPA induced the formation of elongated neurite-like processes in the amelanotic neural crest cells which differed in their cytoskeletal structure from the dendritic processes of normal trunk melanocytes. These TPA-blocked pigment cells with elongated processes bear a striking morphological resemblance to presumptive myoblasts, chondroblasts, and fibroblasts treated with the tumor promoter.

Animals↗
PubMed1980

12-O-tetradecanoylphorbol-13-acetate-induced changes in sulfated proteoglycan synthesis in cultured chondroblasts.

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) rapidly blocks the terminal differentiation of normal cultured chondroblasts. In TPA, the chondroblasts lose their characteristic polygonal morphology and initiate the synthesis of an atypical type IV sulfated proteoglycan. This atypical proteoglycan has lower molecular size, shorter polysaccharide chains, and different 4S-disaccharide:6S-disaccharide ratio in comparison with type IV sulfated proteoglycan from untreated chondroblasts. When removed from TPA, the cells reacquire their characteristic polygonal morphology and reinitiate the synthesis of their typical cartilage-characteristic type IV sulfated proteoglycan. TPA has no readily detectable effect on the type III sulfated proteoglycan synthesized by fibroblasts.

Animals↗
PubMed1979

Differential response of myofibrils and 10-nm filaments to a cocarcinogen.

Multinucleated myotubes containing large numbers of striated myofibrils and large numbers of longitudinally-oriented 10-nm filaments were treated with the cocarcinogen phorbol-12-myristate-13-acetate (PMA) for 24, 48 or 72 hours. The inhibitory effects of PMA on the accumulation of myofibrils was evident within 24 hours, and by 72 hours virtually all striated myofibrils had disappeared. In contrast, the density of the 10-nm filaments was greatly enhanced in these myofibril-depleted myotubes. These effects were not due to a generalized cytotoxicity, for PMA stimulated the replication of the presumptive myoblasts and fibroblasts present in these cultures. 24 hours after removing the PMA, these myotubes assembled a new set of striated myofibrils and the density of 10-nm filaments diminished proportionately.

Animals↗
PubMed1979

Crystalloids of actin-like filaments in the Sertoli cell of the swine testis.

Normal swine testes, congenital cryptorchid swine testes, and normal human tests were exposed to HMM (heavy meromyosin) after either glycerination or saponin treatment in order to determine whether the fine filaments composing the crystalloids in the Sertoli cells of the cryptorchid swine testes bind HMM to form arrowhead complexes. Short bundles of microfilaments observed in the basal part of the Sertoli cells in both normal and cryptorchid testes also bind HMM. Similar bundles of HMM-bound filaments are observed in the vicinity of spermatocytes. The periodicity of the arrowhead complexes is about 35 nm, and all arrowheads on a given filament point in the same direction. In addition, the polarity of the HMM-bound filaments in a given crystalloid or bundle is uni-directional. A mechanism for the formation of the swine crystalloids has been strongly support this hypothesis. Fine filaments of Charcot-Boettcher's crystalloid in human Sertoli cells did not bind HMM. Therefore the fine filaments of the human crystalloid are not actin-like in nature.

Actins↗
PubMed1979

Fibronectin alters the phenotypic properties of cultured chick embryo chondroblasts.

The state of chick embryo chondroblasts in culture was found to be sensitive to both fibronectin and another substance(s) (activity A) which could be extracted from chick embryo fibroblasts with 1 M urea or from conditioned medium. In the presence of either of these activities at concentrations of 25-150 micrograms/ml, chondroblasts, which normally grow as mixed cultures of floating and adherent cells, all immediately became attached to the tissue culture dish and spread. After several days, the morphology of these typically epithelioid cells became fibroblastic. This did not involve a selection process, since the effect was reversible. The synthetic program of these cells was also dramatically modified: the cultures no longer synthesized the chondroblast-unique type IV sulfated proteoglycan and began synthesizing alpha 2 collagen chains typical of fibroblastic or early limb bud cells. Fibronectin was resolved from activity A by gelatin affinity chromatography or gel filtration. Both activities were trypsin-sensitive. The two activities differed, however, on the basis of how the protein fractions in which they were found migrated in SDS-polyacrylamide gels, their specific activities and their effects on cell morphology and cell growth.

Animals↗
PubMed1979

Redistribution of intermediate filament subunits during skeletal myogenesis and maturation in vitro.

The distribution of intermediate filament (IF) subunits during maturation of skeletal myotubes in vitro was examined by immunofluorescence, using antibodies against two different types of chick IF subunits: (a) 58-kdalton subunits of fibroblasts (anti-58K), and (b) 55-kdalton subunits of smooth muscle (anti-55K). Anti-58K bound to a filament network in replicating presumptive myoblasts and fibroblasts, as well as in immature myotubes. The distribution in immature myotubes was in longitudinal filaments throughout the cytoplasm. With maturation, staining of myotubes by anti-58K diminished and eventually disappeared. Anti-55K selectively stained myotubes, and the fluorescence localization underwent a drastic change in distribution with maturation--from dense, longitudinal filaments in immature myotubes to a cross-striated distribution in mature myotubes that was associated with the I--Z region of myofibrils. However, the emergence of a cross-striated anti-55K pattern did not coincide temperally with the emergence of striated myofibrils, but occurred over a period of days thereafter.

Animals↗
PubMed1979

Differential location of different types of intermediate-sized filaments in various tissues of the chicken embryo.

The location of constitutive proteins of different types of intermediate-sized (about 10 mm) filaments (cytokeratin, vimentin, desmin, brain filament protein) was examined in various tissues of 11--20 day chick embryos, using specific antibodies against the isolated proteins and immunofluorescence microscopy on frozen sections and on isolated serous membrane. The tissues studied which contained epithelia were small intestine, gizzard, esophagus, crop, liver, kidney, thymus, mesenteries, and epidermis. The results show that the different intermediate filament proteins, as seen in the same organ, are characteristic of specific lines of differentiation: Cytokeratin filaments are restricted to--and specific for--epithelial cells; vimentin filaments are seen--at this stage of embryogenesis--only in mesenchymal cells, including connective tissue, endothelial and blood cells, and chondrocytes; filaments containing protein(s) related to the subunit protein prepared from gizzard 10 nm filaments (i.e., desmin) are significant only in muscle cells; and intermediate filament protein of brain, most probably neurofilament protein, is present only in nerve cells. We conclude that for most tissues the expression of filaments of cytokeratin, vimentin, desmin, and neurofilament protein is mutually exclusive, and that these protein structurees provide useful markers for histochemical and cytochemical differentiation of cells of epithelial, mesenchymal, myogenic, and neurogenic differentiation.

Animals↗