摘要:

AbstractThe morphology and fine structure of day 12 rat embryonic mesenchyme from forelimb bud, mandibular arches, and frontonasal prominence is described as the cells undergo chondrogenesis in high density, micromass culture. The cultures began as a multilayered “pavement” of flattened mesenchymal cells, 3–4 deep, with moderate intercellular space but little identifiable electron‐dense extracellular matrix. Pre‐cartilage condensations, which consisted of aggregates of cells which had rounded up, displaying little or no intercellular space, formed within the first 24 h in limb mesenchyme and after an additional 24 h in mandibular and frontonasal cultures. Gap junctions occur between these cells, indicating a phase of direct cell‐cell communication. Chondrogenesis within these aggregates began within the next 24 h in limb cultures but was delayed an additional 24–48 h in the frontonasal and especially in mandibular cultures. The aggregates in both limb and mandibular mesenchyme form discrete nodules bordered by a perichondrium consisting of 2–3 layers of flattened cells. Evidence from late stage mandibular cultures suggests that chondroblasts are added to the nodules from the perichondrium, as occurs in vivo. By contrast, the frontonasal cartilage is initially unbordered and forms anastomosing trabecular arrays. Some of these arrays fuse into larger structures with time, but others become surrounded by proceeds. The sequence of cartilage matrix production, as revealed in long‐term facial cultures, appears to occur in three stages, an early phase in which the extracellular matrix consists primarily of proteoglycans, followed by a phase of homogeneous collagen‐proteoglycan matrix and a mature, territorial matrix. In all three cultures the cartilage ultimately produced resembles mature rat hyaline cartilage with chondroblasts surrounded by a territorial matrix of type II collagen and proteoglycan granules. ©

ISSN:1059-910X    

DOI:10.1002/jemt.1070280602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractCartilage is an important tissue in skeletogenesis, in the growth of long bones, and as a flexible component of the mature skeleton. The extracellular matrix proteins type II collagen and aggrecan comprise 90% of the matrix and are characteristic of cartilage. Type II collagen provides structural integrity to the tissue, while aggrecan confers resiliency. The quantity of type II procollagen is controlled at the level of transcription of mRNA from the COL2A1 gene. In addition, type II procollagen can be expressed in two isoforms by differential splicing of the primary gene transcript, a post‐transcript, a post‐transcriptional control mechanism. The two mRNAs either include exon 2 (type IIA) or exclude exon 2 (type IIB) which encodes the major portion of the amino (NH2)‐propeptide [Ryan and Sandell (1990), J. Biol. Chem., 265:10334–10339]. The aggrecan gene also encodes alternative splice forms that may be developmentally expressed. The regulation of aggrecan splicing or transcription has not been studied in detail. To determine the spatial and temporal patterns of expression of extracellular matrix in the development of cartilage, we have examined the expression of type II collagen and aggrecan during chondrogenesis in the vertebral column and during elongation of a newborn growth plate. Our results indicate that there is a developmental sequence of type II collagen splice form expression during chondrogenesis with type IIA expressed in prechondrocytes and type IIB expressed in chondrocytes. During elongation of the growth plate, mature chondrocytes express type IIB procollagen and then differentiate into hypertrophic chondrocytes and initiate expression of type X collagen. In all cases, aggrecan was coordinately expressed with type IIB procollagen. As cartilage‐like proteins have been observed in more primitive structures such as notochord, the expression of type II collagen mRNAs was also examined in the notochordal remnants of the vertebral column. In the notochord, the predominant collagen expressed was the type IIA collagen prechondrocyte isoform. Notochordal cells also expressed mRNAs more characteristic of fibroblasts such as versican and decorin: low expression of type I collagen, type IIB collagen, and aggrecan were observed. © 1994 Wiley‐Liss, IncThis Article is a US Government work and, as such, is in the public domain in the United States

ISSN:1059-910X    

DOI:10.1002/jemt.1070280603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractDuring the process of endochondral bone formation, chondrocytes undergo a series of complex maturational changes. Our recent studies indicate that this maturational process is influenced by the vitamin. A derivative retinoic acid (RA). To learn how this agent regulates chondrocyte development, we characterized matrix gene expression during maturation of cartilage cells in chick sternum. RNAs were isolated from the cephalic portion of day 13, 14, 16, 18, and 20 chick embryo sternum and analyzed via northern blots. Type II collagen RNA levels remained fairly constant during this developmental period. In contrast, expression of type X collagen and alkaline phosphatase (APase) genes was first detected at day 16, followed by that of ostenection (ON) and osteopontin (OP). To explore the mechanisms triggering these changes, chondrocytes were isolated from the cephalic portion of day 17–18 sternum (US cells) and grown in monolayer in standard serum‐containing medium. After 3 weeks in culture, most of the cells enlarged and became type X collagen‐positive, but they exhibited low APase activity and contained only trace amounts of ON and OP mRNAs. Treatment of parallel 3‐week‐old cultures with RA (10–100 nM) rapidly increased expression of the APase, ON, and OP genes severalfold. In concert with a significant increase in APase activity, there was abundant calcium accumulation in the RA‐treated cultures. Electron microscopy confirmed the formation of large matrix‐associated mineral crystals and the presence of numerous matrix vesicles. The effects of RA were also studied in cultures of immature chondrocytes isolated from the caudal portion of sternum (LS cells). In these cells, RA failed to induce high levels of APase activity, ON and OP gene expression, and mineralization; instead, it greatly promoted cell proliferation. Thus RA appears to have major, stage‐specific effects on the maturation program of chondrocytes. The retinoid rapidly induces expression of late maturation genes and activates mineralization of the cartilage matrix. © 19

ISSN:1059-910X    

DOI:10.1002/jemt.1070280604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWhen chick limb‐bud mesenchymal cells are plated in micromass culture, they differentiate to form a mineralizable cartilage matrix. Previous studies have demonstrated that, when the total inorganic phosphate concentration of the medium is adjusted to 3–4 mM by adding inorganic phosphate to the basal medium, the mineralized matrix formed resembles that of chick calcified cartilage in ovo. When the high‐energy phosphates adenosine 5′‐triphosphate (ATP) or creatine phosphate are used as supplements in place of inorganic phosphate, the mineralized matrix as analyzed by electron microscopy and Fourier transform infrared microscopy is also similar to that in ovo. This is in marked contrast to the mineralized matrix formed in the presence of 2.5–5 mM β‐glycerophosphate, where mineral deposition is random and mineral crystal sizes in general are larger. This is also in contrast to the known ability of ATP to inhibit mineral deposition in solution in the absence of cells.In the differentiating mesenchymal cell culture system, ATP does not alter the rate of cell proliferation (DNA content), the rate of matrix synthesis (3H‐leucine uptake), the mean crystallite length, or the rate of mineral deposition (45Ca uptake) when contrasted with cultures supplemented with inorganic phosphate. However, ATP does increase the mineral to matrix ratio, especially around the edge of the culture, where a type I collagen matrix is present. It is suggested that ATP promotes mineral deposition by providing a high‐energy phosphate source, which may be used to phosphorylate extracellular matrix proteins and to regulate calcium flux through cell membranes. © 1

ISSN:1059-910X    

DOI:10.1002/jemt.1070280605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractGrowth plate chondrocytes play a pivotal role in promoting longitudinal bone growth. The current review represents a brief survey of the phenomena involved in this process at the cellular level; it delineates the contributions made by various activities during the course of the chondrocyte life cycle, notably proliferation and hypertrophy, and illustrates how the relative contributions may be modulated according to the particular needs of an organism at critical phases of growth. The cellular mechanisms by which a few well characterized growth‐promoting substances exert their influences are discussed in the light of recent findings pertaining to epiphyseal plate chondrocytes in vivo. © 1994 Wiley‐Liss,

ISSN:1059-910X    

DOI:10.1002/jemt.1070280606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIliac crest biopsies are important in the detection of human skeletal dysplasias. Therefore, culture of these cells may serve as a valuable method for studying proteoglycan metabolism in chondrocytes of individuals with skeletal abnormalities. Morphological and biochemical studies were performed on human iliac crest chondrocytes grown in monolayer and in agarose gels. Two proteoglycan populations of different hydrodynamic size and glycosaminoglycan composition were synthesized by cells grown in monolayer. Chondrocytes cultured in an agarose gel for 2 weeks synthesized proteoglycans identical to those of the native tissue with respect to hydrodynamic size and glycosaminoglycan chain length. However, the ratio of chondroitin‐6‐sulfate to chondroitin‐4‐sulfate was higher than in the native tissue. This ratio was not influenced by different sulfate concentrations in the medium. Moreover, treatment with ascorbic acid did not influence proteoglycan synthesis; however, there was a pericellular accumulation of proteoglycans. © 1994 Wiley

ISSN:1059-910X    

DOI:10.1002/jemt.1070280607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe electron beam induced current technique was used to study electron energy loss in amorphous hydrogenated silicon a‐Si:H. This study leads to the determination of the electron generation function which is needed when using the variable energy electron beam induced current technique (EBIC) analysis of a‐Si:H device. A series of identicaln‐i‐pa‐Si:H diodes with a thin aluminium top electodes were fabricated and varying thicknesses of a‐Si:H layer were deposited on it. In EBIC measurements, then‐i‐pdiode was reverse biased at maximum potential. The electron range of a‐Si:H was determined directly by measuring the energy at which the electron beam is completely stopped in the top layer and no carrier generation is possible in then‐i‐pdiode. The generation function is then deduced from EBIC contrast measurements between the aluminium electrode and the top a‐Si:H layer.

ISSN:1059-910X    

DOI:10.1002/jemt.1070280608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070280601

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY