Biomedical subjects

A I Caplan

Publications and source records attributed to A I Caplan.

At least 19 recordsLinked to original sources

PubMed1992

Collagen gene expression during chondrogenesis from chick periosteum-derived cells.

Chick periosteum-derived cells, which do not enter the chondrogenic cell lineage during normal bone development and growth, exhibit chondrogenic potential in high cell density culture conditions. In such cultures, collagen gene expression was temporally analyzed at the mRNA level by a reverse transcription PCR (RT-PCR) procedure, which showed that alpha 1(II) and alpha 1(IX) collagen mRNAs are coordinately increased, coincident with the onset of overt chondrogenesis, and subsequently decreased as chondrocytes exhibited hypertrophic characteristics. alpha 1(X) collagen mRNA was detected well before the onset of chondrogenesis and markedly increased along with the hypertrophic change. For alpha 2(I) collagen, both the bone/tendon form and the cartilage form of mRNA were detected throughout the culture period. This culture system provides an experimental vehicle capable of investigating the molecular events involved in the full range of chondrogenic differentiation starting from uncommitted periosteum-derived mesenchymal stem cells.

Animals↗

PubMed1992

Partial biochemical and immunochemical characterization of avian eggshell extracellular matrices.

There is evidence to suggest that extracellular matrix molecules, such as proteoglycans, are involved in the regulation of mineral deposition in calcifying tissues. One mineralizing system which is characterized by extremely rapid mineralization is the hen eggshell. This eggshell consists of a pair of nonmineralized eggshell membranes subjacent to the calcified eggshell proper; the eggshell proper is organized into palisades (columns) of mineralized matrix separated by pores. Between the membranes and the shell proper are compacted foci of tissue called mammillary knobs, which are thought to be sites where mineralization is initiated. Previous work from this laboratory has shown the presence of types I, V, and X collagen in the shell membranes. To address the question of the possible role of proteoglycans and glycosaminoglycans in mineralization of the eggshell, two approaches were used. First, immunohistochemistry was performed with monoclonal antibodies to various proteoglycan and glycosaminoglycan epitopes. This analysis indicates that different glycosaminoglycans are localized to discrete regions within the eggshell. Dermatan sulfate is present within the matrix of the shell proper and, to a lesser extent, the mammillary knobs and the outer portion of the shell membranes. In contrast, keratan sulfate is found in the shell membranes and prominently in the mammillary knobs. Interestingly, different keratan sulfate antibodies immunostain distinct regions of the eggshell, which suggests that various types of keratan sulfate are distributed differently. The second approach utilized was to extract the eggshell membranes and recover anionic molecules by anion-exchange chromatography. This resulted in the extraction of material which was recognized by antibodies to keratan sulfate, but not to chondroitin sulfate. This material was very large, as evidenced by its elution in the void volume of a Sepharose CL-2B column. The large size may be due to the extensive cross-links known to occur in the eggshell. If eggshell membranes are extracted at elevated temperature, the material recovered is of much smaller size. These results indicate that molecules recognized by antibodies to glycosaminoglycans are present in the eggshell, and their localized distribution relative to the calcified matrix suggests that they may be involved in the regulation of mineral deposition.

Animals↗

PubMed1992

Cell surface antigens on human marrow-derived mesenchymal cells are detected by monoclonal antibodies.

Human bone marrow has been shown to contain mesenchymal cells, which fabricate the connective tissue network of the marrow called the stroma. A subset of these marrow-derived mesenchymal cells can be isolated, expanded in culture, and then induced to differentiate into bone-producing osteoblasts and ultimately osteocytes when placed in the proper environment. At present, there are no methods for definitively identifying these cells in human marrow tissue or following their differentiation into osteogenic phenotypes. Therefore, we culture-expanded, marrow-derived mesenchymal cells from human donors and used these cells to immunize cells from human donors and used these cells to immunize mice whose spleens were used to generate hybridoma cell lines, which secrete antibodies to antigens on the cell surface of these culture-expanded mesenchymal cells. Hybridoma culture supernatants were successively screened against highly enriched samples of culture-expanded, marrow-derived mesenchymal cells in cryosections and live cell cultures to identify unique cell surface antigens. Positive clones were then screened against cell suspensions of whole and fractionated marrow to identify hybridomas whose supernatants were nonreactive with marrow hemopoietic cells. Three hybridoma cell lines, SH2, SH3, and SH4, were identified; these hybridomas secrete antibodies that recognize antigens on the cell surface of marrow-derived mesenchymal cells, but fail to react with marrow-derived hemopoietic cells. Additional tissue screening reveals unique tissue distributions for each of the recognized antigens, which suggests different antigen recognition for each antibody. However, all three antibodies fail to react with the cell surface of osteoblasts or osteocytes, suggesting that the antigens recognized by these antibodies are developmentally regulated and specific for primitive or early-stage cells of the osteogenic lineage.

Antibodies, Monoclonal↗

PubMed1992

Characterization of cells with osteogenic potential from human marrow.

Studies using animal tissue suggest that bone marrow contains cells with the potential to differentiate into cartilage and bone. We report the extension of these studies to include human marrow. Bone marrow from male and female donors of various ages was obtained either from the femoral head or as aspirates from the iliac crest, and introduced into culture. Culture-adherent cells were expanded, subcultured, and then tested for bone and cartilage differentiation potential utilizing two different in vivo assays in nude mice. One assay involved subcutaneous implantation of porous calcium phosphate ceramics loaded with cultured, marrow-derived, mesenchymal cells; the other involved peritoneal implantation of diffusion chambers, also inoculated with cultured, marrow-derived, mesenchymal cells. Histological evaluation showed bone formation in ceramics implanted with cultured, marrow-derived, mesenchymal cells originating from both the femoral head and the iliac crest. Immunocytochemical analysis indicates that the bone is derived from the implanted human cells and not from the cells of the rodent host. No cartilage was observed in any of these ceramic grafts. In contrast, aliquots from the same preparations of cultured, marrow-derived, mesenchymal cells failed to form bone or cartilage in diffusion chambers. These data suggest that human marrow contains cells with osteogenic potential, which can be enriched and expanded in culture. Our findings also suggest that subcutaneous implantation of these cells in porous calcium phosphate ceramics may be a more sensitive in vivo assay than diffusion chambers for measuring their osteogenic lineage potential.

Animals↗

PubMed1992

Osteogenesis in marrow-derived mesenchymal cell porous ceramic composites transplanted subcutaneously: effect of fibronectin and laminin on cell retention and rate of osteogenic expression.

Cultured-expanded rat marrow-derived mesenchymal cells differentiate into osteoblasts when combined with a porous calcium phosphate delivery vehicle and subsequently implanted in vivo. In this study, the effects of ceramic pretreatment with the cell-binding proteins fibronectin and laminin on the osteogenic expression of marrow-derived mesenchymal cells were assessed by scanning electron microscopy, [3H]-thymidine-labeled cell quantitation, and histological evaluation of bone formation. Scanning electron microscopic observations showed that marrow-derived mesenchymal cells rapidly spread and attach to both fibronectin- or laminin-adsorbed ceramic surfaces but retain a rounded morphology on untreated ceramic surfaces. Quantitation of [3H]-thymidine labeled cells demonstrated that laminin and fibronectin preadsorbed ceramics retain approximately double the number of marrow-derived mesenchymal cells than do untreated ceramics harvested 1 wk postimplantation. Histological observations indicate that the amount of time required to first detect osteogenesis was shortened significantly by pretreatment of the ceramic with either fibronectin or laminin. Fibronectin- and laminin-coated ceramic composite samples were observed to contain bone within 2 wk postimplantation, while in untreated ceramic the earliest observation of bone was at 4 wk postimplantation. A comparison was made of the initial cell-loading, in vivo cell retention characteristics, and rate of osteogenesis initiation of marrow-derived mesenchymal cells on two types of ceramic with different pore structure and chemical composition, with and without preadsorption with fibronectin or laminin. "Biphasic" ceramics contain randomly distributed pores 200-400 microns in diameter, and "coral-based" ceramics have continuous pores of approximately 200 microns in diameter. Laminin or fibronectin preadsorption significantly increases the number of cells retained in all ceramic test groups by day 7 postimplantation. In addition, by day 7 postimplantation, the biphasic ceramics retain a significantly greater number of cells for all test groups than do coral-based ceramics. The biphasic ceramics consistently have more specimens positive for bone with the identical cell-loading conditions used throughout this study. These results indicate that the retention of cells within the ceramic is an important factor for optimization of marrow mesenchymal cell initiated bone formation. The retention of cells within ceramics is augmented by the adsorption of the cell-binding proteins laminin and fibronectin, but this effect varies depending on ceramic pore structure and/or chemical composition.

Animals↗

PubMed1992

Culture-expanded periosteal-derived cells exhibit osteochondrogenic potential in porous calcium phosphate ceramics in vivo.

Chick tibial periosteal cells were enzymatically disaggregated, introduced into cell culture, and subcultured. These subcultured cells were combined with porous calcium phosphate ceramics and implanted into a subcutaneous site in athymic mice as an immunocompatible host to test the in vivo osteochondrogenic potential of this composite graft. These cells eventually gave rise to bone tissue in the pores of ceramics at the heterotopic implantation sites. The process of bone formation occurred through two different mechanisms: Intramembranous bone formation occurred at the peripheral pores of ceramics early, and endochondral bone formation occurred in the central pores later. Cultured chick muscle fibroblasts of the same-aged donor as controls did not form bone or cartilage under identical conditions to those of cultured periosteal-derived cells. These results raise the possibility that composite graft of cultured periosteal-derived cells and porous ceramics can be clinically used as a bone graft substitute in situations requiring bone augmentation or regeneration.

Animals↗

PubMed1991

Three-dimensional reconstruction and cross-sectional anatomy of the thigh musculature of the developing chick embryo (Gallus gallus).

The technique of graphical reconstruction by orthogonal projection of serial sections is used to generate three-dimensional models of embryonic chick thigh musculature at Hamburger-Hamilton ('51) stages 36 (day 10) and 39 (day 13). Unique and conserved anatomical landmarks are described, which can be used to specify position along the proximo-distal axis of the thigh from cross-sectional appearance. These landmarks provide an important reference for both current and future experimentation in which a precise developmental site must be systematically and repeatedly sampled.

Animals↗

PubMed1991

Culture-expanded human periosteal-derived cells exhibit osteochondral potential in vivo.

Periosteal cells were enzymatically liberated from human rib periostea obtained from autopsies of 37 donors with an age distribution ranging from 25 weeks of gestation to 88 years old. These cells were introduced into cell culture and subcultured when they reached confluence. After subculture, the adherent periosteal-derived cells showed a nondescript, fibroblast-like morphology in cell culture. The cells from various passages of each donor were tested for in vivo osteochondrogenic potential with three different assay methods in athymic mice: (a) inoculation assay--the cells were directly inoculated into a subcutaneous site, (b) porous ceramics assay--the cells were combined with porous calcium phosphate ceramics, and this composite graft was implanted into a subcutaneous site, and (c) diffusion chamber assay--the cells were loaded into diffusion chambers and cultured in the peritoneal cavity. Frozen-preserved and recultured periosteal-derived cells were also assayed in the same way. In cases of donors younger than 19 years old, cultured, periosteal-derived cells from up to several passages consistently formed bone and/or cartilage in each of the three assays. Frozen-preserved and recultured cells from these donors also formed bone and/or cartilage after introduction into the three in vivo assays. In cases of donors older than 22 years of age, cultured, periosteal-derived cells formed neither bone nor cartilage in vivo. Cultured muscle fibroblasts from some of the same donors did not form bone or cartilage when assayed in vivo under identical conditions. These results suggest that periosteal cells with osteochondrogenic potentials can be liberated from the periosteum of a rib of human donors up to a certain age. Importantly, this potential is retained after enzymatic liberation, cell culture, subculturing, and freeze preservation. The present results suggest that culture-expanded human periosteal-derived cells from young donors may be useful in the repair of skeletal defects to foster cell-mediated regeneration of skeletal tissues, and that this methodology can be used to elucidate cellular, molecular, and genetic disorders in various metabolic bone diseases and skeletal dysplasias.

Adult↗

PubMed1991

Mesenchymal stem cells.

Bone and cartilage formation in the embryo and repair and turnover in the adult involve the progeny of a small number of cells called mesenchymal stem cells. These cells divide, and their progeny become committed to a specific and distinctive phenotypic pathway, a lineage with discrete steps and, finally, end-stage cells involved with fabrication of a unique tissue type, e.g., cartilage or bone. Local cuing (extrinsic factors) and the genomic potential (intrinsic factors) interact at each lineage step to control the rate and characteristic phenotype of the cells in the emerging tissue. The study of these mesenchymal stem cells, whether isolated from embryos or adults, provides the basis for the emergence of a new therapeutic technology of self-cell repair. The isolation, mitotic expansion, and site-directed delivery of autologous stem cells can govern the rapid and specific repair of skeletal tissues.

Animals↗

PubMed1991

Immunohistochemical localization of a approximately 66 kD glycosylated phosphoprotein during development of the embryonic chick tibia.

Localization of a approximately 66 kD glycosylated phosphoprotein during morphogenesis of the embryonic chick tibia has been accomplished using immunohistochemistry. Although initial expression of the tibial osteoblast phenotype is detected as early as stage 28.5, with the deposition of osteoid matrix beginning at stage 30, little or no immunoreactivity against the approximately 66 kD glycosylated phosphoprotein is observed in pre-osteoblasts, osteoblasts, osteocytes, or in the uncalcified osteoid matrix during the early events of tibia development. Immunoreactivity was first observed at stage 32 when mineralization of the osteoid matrix is initiated. At this and all later stages, the phosphoprotein is located almost exclusively in the extracellular matrix at the mineralization front with essentially no detectable staining in the adjacent unmineralized osteoid matrix. Similarly, no cellular staining is observed when even the lightly mineralized extracellular matrix is strongly immunoreactive. Only scant immunostaining is present over the heavily mineralized regions, although demineralization of these areas with EDTA exposes a low intensity, punctate staining pattern. Additionally, cryosections of developing calvaria stained with this antiserum only display reactivity in regions of bone matrix undergoing mineralization. These localization studies support the hypothesis that this phosphoprotein is intimately associated with the process of bone matrix mineralization in the developing chick long bone.

Animals↗

PubMed1991

In vitro differentiation of bone and hypertrophic cartilage from periosteal-derived cells.

Periosteal cells were enzymatically liberated from the tibiae of young chicks, introduced into cell culture, and allowed to reach confluence. The morphology of the cells gave the impression of a relatively homogeneous population of fibroblast-like cells. These cultured cells did not overtly express osteogenic or chondrogenic properties as judged by their morphology and the lack of reactivity with probes to phenotype-specific antigens of osteoblasts or chondrocytes. The cells were then replated at relatively high density and chronologically evaluated for the differentiation of bone and cartilage. These replated cells formed a multi-layer of fibroblast-like cells, the top portion of which eventually differentiated into bone tissue as evidenced by the presence of mineralization and immunocytochemical reactivity to bone Gla protein- and osteocyte-specific probes. Cells below this distinctive top layer differentiated into chondrocytes, which eventually further developed into hypertrophic chondrocytes as evidenced by their morphology and the presence of immunoreactive type X collagen in the matrix. Mineralization was also observed in the territorial matrix of these hypertrophic chondrocytes, when the culture was augmented with beta-glycerophosphate. Periosteal-derived cells replated at a lower density as controls did not show signs of osteochondrogenic differentiation. These observation suggest that periosteal-derived cells of young chicks contain mesenchymal cells which possess the potential to undergo terminal differentiation into osteogenic or chondrogenic phenotypes depending on local environmental or positional cues.

Animals↗

PubMed1991

Osteogenic potential of culture-expanded rat marrow cells as assayed in vivo with porous calcium phosphate ceramic.

It has been established that, when whole marrow is introduced into porous calcium phosphate ceramic, bone forms on the walls of the pores. To extend earlier studies, bone marrow cells derived from the femora of inbred rats were introduced into tissue culture and the adherent cells cultivated, mitotically expanded, passaged, harvested, placed in small cubes of porous calcium phosphate ceramics and grafted into subcutaneous sites of syngeneic rats. Marrow-derived, cultured mesenchymal cells introduced into ceramics showed strong osteogenic potential, with bone forming in the pore regions of ceramics as early as 2 wk after implantation. Osteogenesis could be observed after the eighteenth passage. With increasing passage number, the initiation of osteogenesis and the apparent rate of bone formation declined and the course of osteogenesis was delayed. In the future, it may be possible to culture marrow cells as a source for reparative cells for implantation back into autologous in vivo sites.

Animals↗

PubMed1991

The dynamics of compartmentalization of embryonic muscle by extracellular matrix molecules.

In order to delineate the role of proteoglycans in muscle development, the immunohistological localization of glycosaminoglycans and proteoglycan core proteins was studied in embryonic chick leg at Hamburger-Hamilton stages (St.) 36, 39, 43, and 46, and at 2 weeks posthatching. A specific anatomical landmark was chosen (the junction between the pars pelvica and the pars accessoria of the flexor cruris lateralis muscle) in order to ensure the study of anatomically equivalent sites. Frozen cross sections were immunostained with monoclonal antibodies to chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and keratan sulfate glycosaminoglycans; to the core proteins of muscle/mesenchymal chondroitin sulfate proteoglycan, dermatan sulfate proteoglycan, and basement membrane heparan sulfate proteoglycan; and to laminin and tenascin. Extracellular matrix zones corresponding to the endomysium, perimysium, epimysium, basement membrane, and myotendinous junction each show characteristic immunostaining patterns from St. 36 to St. 46 and have unique matrix compositions by St. 46. In some cases, there is a sequential or coordinate expression of epitopes, first in the epimysium, then the perimysium, and last in the endomysium. Dermatan sulfate proteoglycan is detected in the epimysium at St. 36, in the perimysium at St. 39 (there is no perimysium structure at St. 36), and is not detected in the endomysium until St. 43. A putative mesenchymal proteoglycan core protein (reactive to the monoclonal antibody MY-174) is detected at St. 39 in both epimysium and perimysium, but is not detected in the endomysium until St. 43. Keratan sulfate antibody immunostains epimysium at St. 39 and perimysium at St. 46, but is never detected in the endomysium. Some epitopes are expressed independently in each of the extracellular matrix zones: antibody to tenascin stains only a subset of the epimysium, at the myotendinous junction; and heparan sulfate proteoglycan and laminin are detected only in the endomysium. Between St. 36 and St. 39, the muscle/MY-174-reactive proteoglycan core protein staining decreases in intensity in the endomysium and becomes positive in the epimysium and perimysium. An inverse relationship is found between (1) the disappearance of muscle/MY-174-reactive proteoglycan core protein staining at the surface of myotubes from St. 36 to St. 39 and (2) the infiltration of laminin and heparan sulfate proteoglycan staining encompassing groups of myotubes (St. 36) to circumferential staining of all myotubes (St. 39).(ABSTRACT TRUNCATED AT 400 WORDS)

Aggrecans↗

PubMed1991

Generation of a monoclonal antibody against avian small dermatan sulfate proteoglycan: immunolocalization and tissue distribution of PG-II (decorin) in embryonic tissues.

Chick embryonic skeletal muscle synthesizes three major types of proteoglycans: large chondroitin sulfate proteoglycans, small dermatan sulfate proteoglycans and small heparan sulfate proteoglycans. A monoclonal antibody has been raised which recognizes the small dermatan sulfate proteoglycan. Immunoblot analysis of a partially purified preparation of skeletal muscle proteoglycans indicates that the antibody reacts with a molecule which migrates with an estimated Mr of 100,000. Prior treatment of the proteoglycans with chondroitinase results in immunostaining of a species of estimated Mr 45,000. These values for the intact proteoglycan and its core protein suggest that the antibody is directed against a proteoglycan of the PG-II or decorin class. Immunohistochemistry indicates a widespread distribution of the proteoglycan, which is localized in connective tissue septa of skeletal and cardiac muscle, dermis, tendon, bone, perichondrium and cornea. Immunoblot analysis of the proteoglycan core proteins from these tissues demonstrates that the antibody recognizes the same 45,000-dalton band in each tissue. The widespread tissue distribution is also consistent with the antibody being directed against an epitope of PG-II. Neither the glycosaminoglycan chains nor N-linked oligosaccharides are required for reactivity and the antibody cross-reacts with other avian material, but not mammalian. This antibody, which has been designated CB-1, reveals developmental stage-specific changes in the deposition of PG-II in embryonic limb bud and skeletal muscle.

Animals↗

PubMed1991

The fabrication and collagenous substructure of the eggshell membrane in the isthmus of the hen oviduct.

The eggshell of the chicken consists of a bi-layered shell membrane overlaid with a thick, calcified shell matrix. The shell membranes and matrix are deposited onto the egg as it passes through the oviduct. To assess the temporal and spatial aspects of the fabrication of type X collagen within the eggshell extracellular matrix, the immunohistochemical localization of type X collagen was studied in three regions of the hen oviduct (magnum, isthmus and uterus), in the membranes of uncalcified eggshells obtained from the oviduct prior to mineral deposition and in eggshell membrane and calcified eggshell matrix. Additionally, immunohistochemical localization of type I and III collagens was done in order to determine possible co-localization of collagen types or to define tissue compartments. None of the collagen epitopes assayed was found in the shell matrix. Type X collagen epitope was immunohistochemically localized only to the epithelial cell layer lining the isthmus region of the oviduct and in the shell membranes of both uncalcified and calcified eggshells. Antitype III collagen monoclonal antibody delineated the inter-tubular gland connective tissue of the oviduct and was negative in the shell layers under conditions which gave strong connective tissue reactivity. Type I collagen epitope was exposed after pepsin treatment of the tissue and co-localizes with the distribution of type III collagen. Type I collagen co-localized with type X collagen in the shell membranes of uncalcified shells. The type I collagen epitope was reactive in the shell membrane of the uncalcified shells, but could only be detected in calcified shells following pepsin digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Patterns of glycosaminoglycan/proteoglycan immunostaining in human skin during aging.

Proteoglycans and their component glycosaminoglycans are involved in such cell-cell and cell-matrix interactions as cell adhesion and migration, processes that are essential for embryonic and fetal development. As definitive organs such as skin emerge, structurally different proteoglycans partition into highly defined compartments. In skin, these compartments correspond to morphologically and functionally distinct layers. However, during the normal aging process, the relative amounts of structurally distinct proteoglycans apparently varies independently in each of these layers. This was demonstrated, in an indirect immunocytochemical study, through the use of monoclonal antibodies that detect structurally distinct domains in glycosaminoglycan chains of proteoglycans. Using samples of normal human skin obtained from individuals ranging in age from 20 weeks of gestation to 98 years of age, we determined that a common distribution pattern existed in skin. The epidermis contained chondroitin 4- and keratan sulfates, the basal lamina was the only layer that contained chondroitin 6-sulfate, the papillary and reticular dermis contained principally dermatan sulfate. In addition, antibodies that recognize native domains in chondroitin sulfates identified proteoglycan subsets that partitioned into distinct layers. An important new finding was that the relative amounts of specific types of glycosaminoglycans varied in an age- and layer-dependent manner. In the epidermis there was a notable increase in keratan sulfate beginning at age 50. Chondroitin 6-sulfate, found principally in the basal lamina, decreased after age 60. In the papillary dermis, the amount of dermatan sulfate increased after age 50, whereas the amount of novel chondroitin sulfate epitope, detected by antibody 4C3, decreased with age. Thus, age-related changes in proteoglycan distribution exist and correlate with morphologic and functional changes that occur in the intrinsic process of aging in human skin.

Adolescent↗

PubMed1991

Comparison of the cartilage proteoglycan core protein synthesized by chondrocytes of different ages.

Chondrocytes of different ages synthesize proteoglycans which have structural differences in both the chondroitin sulfate and keratan sulfate glycosaminoglycans. In order to ascertain whether age-dependent differences also occur in the core protein, the chick limb bud mesenchymal cell culture system was utilized to analyze newly synthesized proteoglycan core protein from undifferentiated mesenchymal cells (day 1 and 2), newly differentiated cartilage (day 4), mature cartilage (day 8), and senescent cartilage (day 16). The core protein synthesized at various times was identified by radiolabeling with [3H]leucine and [35S]sulfate immediately prior to extraction and purification. The sizes of the various core protein preparations were compared by electrophoresis on a 3% polyacrylamide gel after partial deglycosylation with chondroitinase AC and keratanase. The proteoglycans from day 4, 8, and 16 cultures each give rise to a single band of approximately 475,000 daltons. The proteoglycans from day 1 and 2 cultures also give rise to the 475,000 dalton band, but each contains several other components which produce a smear of high molecular weight material on the gel. The monomer proteoglycans were incubated with cyanogen bromide and the resultant peptides separated by electrophoresis on a 5-17.5% polyacrylamide gel. The peptide displays of core proteins synthesized on days 4, 8 and 16 are virtually identical in terms of the number and electrophoretic distribution of the core protein peptides. In contrast, proteoglycan core proteins from day 1 and day 2 cultures give rise to peptide displays which resemble those from older cultures in some respects but have distinct features as well. The absence of structural variation in the newly synthesized proteoglycan core proteins from cartilage of different ages suggests that the age-related changes in the structure of the intact proteoglycans result from differences in the glycosaminoglycan biosynthetic machinery rather than alterations in the acceptor molecule (i.e., the core protein).

Aggrecans↗

PubMed1991

Collagens of the chicken eggshell membranes.

An immunohistochemical analysis of the eggshell membranes shows the occurrence of type X collagen while type I collagen was not detected by using an appropriate monoclonal antibody with untreated shell membranes. A positive immuno-reaction for type I collagen was obtained after digestion of the shell membranes with pepsin. These observations indicate the possibility that type I collagen epitope was masked by type X collagen and that type X collagen may serve as an inhibitory boundary for biomineralization.

Acetates↗