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J Sela

Publications and source records attributed to J Sela.

At least 55 records · Page 3Linked to original sources
PubMed1987

Ultrastructural tissue morphometry of the distribution of extracellular matrix vesicles in remodeling rat tibial bone six days after injury.

A study of the distribution of extracellular matrix vesicles on the 6th day of bone healing was performed by methods of transmission electron microscopy combined with computerized morphometry. The vesicles were detected on the electron micrographs and grouped according to their diameters, distance from the calcified front and type. The different types were selected as follows: vesicles with electron-lucent contents, i.e., 'empty'; vesicles with amorphous electron-opaque contents, i.e., 'amorphous'; vesicles containing crystalline depositions, i.e., 'crystal', and vesicles containing crystalline structures with ruptured membranes, i.e., 'rupture'. Most of the vesicles were concentrated between diameters of 0.02 and 0.22 microns. Most of the vesicles were found within a distance of less than 3 micron from the calcified front. The vesicles were distributed according to their types: 'empty', 'amorphous', 'crystal' and 'rupture' in 14, 39, 34 and 13%, respectively. The diameters of the 'crystal' and 'rupture' vesicles were significantly larger than those of the 'empty' and 'amorphous' types. The sequence of distances from the calcified front was recorded as follows: 'rupture', 'crystal', 'amorphous' and 'empty', the 'rupture' type being the closest to the front. The results of the present study confirm the accepted hypothesis on calcification via extracellular matrix vesicles. It is thought that the cell secretes 'empty' vesicles that accumulate amorphous Ca and P to form a hydroxy-apatite crystal. This is followed by rupture of the vesicular membrane. The propagation of the process is accompanied by increase in the vesicular diameter and its approximation to the calcifying front.

Animals↗
PubMed1987

Extracellular matrix vesicle distribution in primary mineralization two weeks after injury to rat tibial bone (ultrastructural tissue morphometry).

Primary mineralization on the 14th day of bone healing served as a model to study the distribution of extracellular matrix vesicles by means of transmission electron microscopy combined with computerized morphometry. Vesicles were traced on electron micrographs and classified according to diameter, distance from the calcified front, and type. The different types were determined as follows: electron-lucent vesicles ("empty"), vesicles with amorphous contents ("amorphic"), vesicles containing crystalline depositions ("crystal"), and vesicles with crystals and ruptured membranes ("rupture"). The majority of the vesicles measured between 0.02 and 0.07 micron and were located at a distance of less than 3 micron from the calcified front. They were distributed according to "empty", "amorphic", "crystal" and "rupture" type in concentrations of 10%, 31%, 51% and 8%, respectively. The diameters of the "rupture" vesicles were significantly larger than those of the "empty" and "amorphic" types. The sequence of their location, starting at the calcified front, ran as follows: "rupture", "crystal", "amorphic" and "empty", with the "rupture" type proximate to the front. According to the working hypothesis on calcification via extracellular matrix vesicles, it is thought that the "empty" vesicles are secreted by the cell and that subsequently amorphous Ca and Pi accumulate intravesicularly to form a hydroxyapatite crystal which, in turn, brings about rupture of the vesicle's membrane. The results of the present study support this theory and, additionally, show that the maturation process is accompanied by an increase of the vesicular diameter and by its approximation to the calcifying front.

Animals↗
PubMed1986

Osteogenesis induced by bone matrix is inhibited by inflammation.

This study was designed to examine the effect of inflammatory reaction elicited by percutaneous tube on bone induction. Inflammation was provoked by different types of biomaterials. In order to evaluate incorporation of percutaneous tubes, bone matrix and subcutaneous tissue, demineralizing bone matrix was implanted in the subcutaneous tissue of rats and was exposed to interaction with inflammatory conditions. Inhibition to the induction of cartilage and bone by the inflammatory process could be clearly demonstrated. It is suggested that the low pH levels, typical to enzymes operative in inflammation are a direct cause for inhibition of chondro and osteogenesis. The process of calcification is characterized by the activation of enzymes in high pH levels.

Animals↗
PubMed1985

Removal of tibial marrow induces increased formation of bone and cartilage in rat mandibular condyle.

The present paper reports alterations in osteogenesis recorded in mandibular condyles 3-18 days after the removal of marrow tissue from tibial bones. Computerized histomorphometric evaluation of undecalcified condyles revealed a considerable increase in the thickness of condylar cartilage, in particular, the zone of provisional calcification. Measurements of the subcartilaginous trabecular bone suggested an increase in the number of osteoblasts and in their activity. The systemic enhancement of osteogenesis may be initiated by circulating factors released at the affected limb during regeneration of the marrow.

Animals↗
PubMed1984

A study of a sample of oral cancer in Israel.

A review of data on oral cancer in Israel revealed a lower incidence and a later onset age than in other countries. These data are reviewed and consideration is given to the high prevalence of smoking and the low incidence of alcoholism in Israel.

Adolescent↗
PubMed1983

Extracellular matrix vesicles in rat bone after parathyroidectomy.

The enzymatic activity of bone matrix vesicles from parathyroidectomized rats was determined and compared to the activity of vesicles from sham operated and normal animals. The vesicles were isolated from the alveolar bone by collagenase digestion and differential centrifugation and further purified on a discontinuous sucrose density gradient. The amount of extractable protein and the activity of alkaline phosphatase, acid phosphatase, and ATPase in the vesicle fractions thus obtained did not differ significantly from the values characteristic of preparations from control rats. It may therefore be suggested that parathyroid hormone depletion and the associated hypocalcemia have no significant effect on the occurrence and phosphatase activity of bone matrix vesicles.

Acid Phosphatase↗
PubMed1983

Correlative morphometric and biochemical analysis of purified extracellular matrix vesicles from rat alveolar bone.

Extracellular matrix vesicles were isolated from rat alveolar bone and purified by either gel filtration or discontinuous sucrose density gradient. Morphometric evaluation of electron-micrographs of pellets of purified and nonpurified vesicle fractions was correlated with the activity of vesicular enzymes. A high correlation was found between the percentage of area occupied by vesicles with electron-dense content (electron-dense vesicle fractional area) and the enzymatic activity. Highest enzymatic specific activities and electron-dense vesicle fractional area were recorded in the "light" vesicle-enriched fraction obtained after equilibrium density centrifugation. These parameters revealed lowest values in the "heavy" vesicle-enriched fraction resolved by the same methods. The combined electron-dense and electron-lucent fractional area (vesicular fractional area) was similar in the different purified fractions. It is therefore suggested that the fraction obtained by gel filtration contains both "light" and "heavy" vesicles. Morphometric study is proposed as an additional criterion for the degree of purification of matrix vesicle preparations.

Acid Phosphatase↗
PubMed1983

Neutral peptidase activities in matrix vesicles from bovine fetal alveolar bone and dog osteosarcoma.

Extracellular matrix vesicles from bovine fetal alveolar bone and from a dog osteosarcoma were isolated by differential centrifugation and then fractionated on a discontinuous sucrose density gradient. The fractions were examined by electron microscopy and were analyzed for protein, alkaline phosphatase, aminotripeptidase, and four different beta-naphthylamidase activities. The low-density peak of enzyme activities was shown by electron microscopy to be much more homogeneous than the crude matrix vesicle fraction. Two major peaks of protein and enzyme activities were present, one in the high and one in the low density layers. There was good correlation between the activities of alkaline phosphatase and the various peptidases in the fractions from the sucrose density gradient. These results indicate a coexistence of peptidase and alkaline phosphatase in matrix vesicles. On the other hand, there was generally no correlation between the peptidase and alkaline phosphatase activities in vesicular specimens from bovine liver obtained in the same way. Most of the peptidase activity and about half of the alkaline phosphatase activity were solubilized from bone matrix vesicles by detergents. The extracted alkaline phosphatase and alanyl beta-naphthylamidase activities were separated from each other on a DEAE-cellulose column.

Alkaline Phosphatase↗
PubMed1983

Primary calcification in remodeling haversian systems following tibial fracture in rats.

Electron micrographs of fracture callus obtained ten days after injury show typical primary matrix vesicle mineralization. In remodeling haversian canals distant from the fracture sites, matrix vesicles and calcifying nodules were observed. The occurrence of these elements was also found to control unfractured tibiae with intramedullary nails but not normal bone. These observations suggest that during haversian remodeling, mineralization after osseous or marrow tissue damage is associated with matrix vesicles.

Animals↗
PubMed1982

Effect of X-ray irradiation on primary mineralization in rat alveolar bone.

The effect of X-ray irradiation on the process of primary mineralization in bone was studied by biochemical and ultrastructural methods. A single dose of 1500R was administered to the head region of rats. The animals were examined immediately after irradiation and 1, 2 and 3 weeks later. Fractions of isolated cells and extracellular matrix vesicles were prepared from the maxillary alveolar bone of irradiated and untreated rats by collagenase digestion and differential centrifugation. The protein content and activities of vesicular phosphatases were determined in both fractions. A continuous decrease in the activity of alkaline phosphatase could be observed in both cell and matrix vesicle fractions during a three-week follow up after irradiation. Acid phosphatase activity decreased only in the vesicle fraction. Transmission electron microscopy of irradiated bone tissue revealed that many matrix vesicles were devoid of intact membranes and apatite crystals. Calcifying nodules were abundant in the matrix without their apparent fusion into larger mineralized structures. It is suggested that irradiation interferes with enzymatic processes associated with primary mineralization.

Alveolar Process↗
PubMed1982

Occurrence of actin-like protein in extracellular matrix vesicles.

Preliminary indications of the occurrence of actin and myosin in crude matrix vesicle preparations have been reported previously. In the present study extracellular matrix vesicles from rat alveolar bone were isolated. They were further purified by a sucrose density gradient. SDS-polyacrylamide gel electrophoresis of the purified vesicles revealed the presence of a polypeptide with a molecular weight of 43 K daltons and with electrophoretic mobility identical to that of blood platelet actin. The limited proteolysis of both 43 K dalton vesicular polypeptide and actin by Staphylococcus aureus-V8-protease revealed three fragments with identical electrophoretic mobility. In addition, the vesicular preparations inhibited the activity of DNase I, a property typical of actin monomers. Filamentous material extracted from matrix vesicles showed ultrastructuraL features of F-actin. Reaction of this material with heavy meromyosin resulted in arrowhead formation, which is characteristic of acto-heavy meromyosin. The occurrence of actin in extracellular matrix vesicles may account for their budding from the osteoblastic plasma membrane, their possible motility in the matrix, and maintenance of the spherical shape.

Actins↗
PubMed1982

Patterns of matrix vesicle calcification in osteomalacia of Gyro mice.

Homozygous Gyro mice manifest widespread abnormalities in the inner ear and other parts of the skeleton. These disorders were attributed to a sex linked dominant gene. In the present study, tissue specimens were obtained from the inner ear and maxillary and tibial bones, and undecalcified samples were processed for light and transmission electron microscopy. Light microscopy revealed osseous changes consistent with osteomalacia. These alterations comprised broad bands of osteoid with partial or complete failure of calcification. Electron micrographs showed longitudinal calcifying fronts composed of hydroxyapatite crystals. Abundance of matrix vesicles could be demonstrated in the extracellular matrix. Many of the vesicles contained crystaline mineral. In addition, calcification alongside collagen fibers was recorded. Occasionally, apatite crystals were attached to plasma membranes. Female and hemizygous male mice showed normal patterns of calcification. The findings in the affected Gyro mice appear to be similar to previously reported changes in human osteomalacia. Further definition of the pathological process in this animal model may be valuable in defining mechanisms operative in the development of osteomalacia in man.

Animals↗
PubMed1982

Correlative clinico-pathological evaluation of oral premalignancy.

In 1972, the World Health Organization's "Meeting of Investigators on the Histological Definitions in Precancerous Lesions" defined a precancerous lesion as a "morphologically altered tissue in which cancer is more likely to occur than in its apparently normal counter part" (Pindborg 1980). There are two generally accepted precancerous lesions in the oral cavity, leukoplakia and erythroplakia (Pindborg 1980). Leukoplakia is currently defined as "a white patch or plaque that cannot be characterized clinically or pathologically as any other disease" (WHO 1978). This definition has no histological connotation and is used in a strictly clinical sense (Pindborg 1980, Banoczy 1977). Erythroplakia is defined as a "bright red velvety plaque which cannot be characterized clinically or pathologically as being due to any other condition" (Pindborg 1980).

Diagnosis, Differential↗
PubMed1982

Calcification patterns of rat condylar cartilage after induced unilateral malocclusion.

Occlusal interferences on right upper molars in rats produced ultrastructural changes in the calcification of ipsilateral condylar cartilage. This was characterized by premature appearance of apatite crystals within extracellular matrix vesicles present in the proliferative cell zone. The normal proliferative cell zone in the rat condyle manifested noncalcifying vesicles. The zone of calcification in rats with an occlusal splint revealed longitudinal calcifying fronts in the vicinity of the chondrocytes. These fronts were composed of haphazardly distributed apatite crystals. These ultrastructural alterations support the generally accepted view that mechanical stimuli induce changes in the process of primary mineralization.

Animals↗
PubMed1982

Primary mineralization of dentin in rats after pulp capping with calcium-hydroxide.

It has been previously reported that short term application of calcium-hydroxide to the dental pulp resulted in the formation of a dentin bridge with matrix vesicle calcification. The present study deals with the induction of reparative dentin in rat molar pulps by direct capping with calcium-hydroxide. The teeth were examined after 21 and 35 days. Transmission electron microscopy (TEM) revealed that the calcification process in the newly formed dentin was characterized by apatite deposition in matrix vesicles and the occurrence of calcifying nodules in the matrix. The persistence of these features of primary mineralization, during the experimental period, was associated with the continuous calcium hydroxide contact with pulp tissue, producing changes in its metabolic state.

Animals↗