Growth of embryonic avian and mammalian tibiae on a relatively simple chemically defined medium

Murine Limb Explant Cultures to Assess Cartilage Development

To investigate chondrocyte biology in an organized structure, limb explant cultures have been established that allow for the cultivation of the entire cartilaginous skeletal elements. In these organ cultures, the arrangement of chondrocytes in the cartilage elements and their interaction with the surrounding perichondrium and joint tissue are maintained. Chondrocyte proliferation and differentiation can thus be studied under nearly in vivo conditions. Growth factors and other soluble agents can be administered to the explants and their effect on limb morphogenesis, gene expression and cell-matrix interactions can be studied. Cotreatment with distinct growth factors and their inhibitors as well as the use of transgenic mice will allow one to decipher the epistatic relationship between different signaling systems and other regulators of chondrocyte differentiation. Here we describe the protocol to culture cartilage explants ex vivo and discuss the advantages and disadvantages of the culture system.

The histological effects of copper and zinc on chick embryo skeletal tissues in organ culture

1. The effects of copper and zinc on organ cultures of chick embryo cartilage and bone maintained in low-trace-metal, chemically defined media for up to 8 d were studied macro-scopically, histologically and histochemically. Length and wet-weight measurement of explants were assessed statistically.

2. No effects were found with Cu concentrations of 0·5–1·5μg/ml medium. Between concentrations of 5 and 40μg Cu/ml medium, lengths and wet-weights of cartilage cultures decreased significantly (P< 0·001) compared with controls. The decrease was directly proportional to increasing Cu concentration, and that of the length was greater with increasing period of culture (P< 0·001).

3. With 5–20μg Cu/ml medium cartilage and bone became yellow in colour, and chondrocytes were swollen, rounded and basophilic. They were detached from their lacunae and the quantity of matrix was reduced. Loss of alkaline phosphatase (EC3.1.3.1) activity and disappearance of glycogen accompanied the degeneration. Osteogenesis ceased, cells failed to divide and mature, lost their enzymes and died. Cu did not accumulate in the bone matrix.

4. The direct toxic effects of Cu for cartilage and bone may underlie some of the skeletal changes in hepatolenticular degeneration (Wilson’s disease).

5. As Zn concentrations were increased from 2·5 to 7·5μg/ml medium, lengths and wet-weights of cartilaginous cultures were significantly increased (P< 0·001). As Zn concentrations were further increased (from 10 to 40μg/ml medium), lengths and wet-weights were significantly decreased (P< 0·001).

6. Zn stimulated chondrocyte division and vacuolation of cytoplasm. With higher Zn concentrations toxic changes of granular basophilia, lacunar detachment and necrosis were seen. Differentiation and functioning of osteoblasts, osteoclasts and chondroclasts were stimulated by Zn.

7. Zn was found in bone matrix, osteoblasts, osteocytes and hypertrophied chondrocytes.

Cartilage explant cultures

To investigate chondrocyte biology in an organized structure, limb explant cultures have been established that allow the cultivation of the entire cartilaginous skeletal elements. In these organ cultures, the arrangement of chondrocytes in the cartilage elements and their interaction with the surrounding perichondrium and joint tissue are maintained. Chondrocyte proliferation and differentiation can thus be studied under nearly in vivo conditions. Growth factors and other soluble agents can be administered to the explants, and their effect on limb morphogenesis, gene expression, and cell-matrix interactions can be studied. Co-treatment with distinct growth factors and their inhibitors as well as use of transgenic mice will allow one to decipher the epistatic relationship between different signaling systems and other regulators of chondrocyte differentiation. Here we describe the protocol to culture cartilage explants ex vivo and discuss the advantages and disadvantages of the culture system.

The classic : a morphogenetic matrix for differentiation of cartilage in tissue culture

This Classic Article is a reprint of the original work by Hiroshi Nogami and Marshall R. Urist, A Morphogenetic Matrix for Differentiation of Cartilage in Tissue Culture. An accompanying biographical sketch of Marshall R. Urist, MD is available at DOI 10.1007/s11999-009-1067-4; a second Classic Article is available at DOI10.1007/s11999-009-1068-3; and a third Classic Article is available at DOI 10.1007/s11999-009-1070-9. The Classic Article is copyright 1970 by the Society for Experimental Biology and Medicine and is reprinted with permission from Nogami H, Urist MR. A morphogenetic matrix for differentiation of cartilage in tissue culture. Proc Soc Exp Biol Med. 1970;134;530-535.

Corticosterone modulates noradrenaline-induced melatonin synthesis through inhibition of nuclear factor kappa B

In chronically inflamed animals, adrenal hormones exert a positive control on the secretion of melatonin by the pineal gland. In this paper, the mechanism of corticosterone as a modulator of melatonin and N-acetylserotonin (NAS) was determined. Rat pineal glands in culture, stimulated for 5 hr with noradrenaline (10 nm), were previously incubated with corticosterone (1.0 nm-1.0 microm) for 48 hr in the presence or absence of the glucocorticoid receptor (GR) antagonist, mifepristone (1.0 microm), the proteasome inhibitor, N-acetyl-leucinyl-leucinyl-norleucinal-H (ALLN, 12.5 microm) or the antagonist of the nuclear factor kappa B (NFkappaB), pyrrolidinedithiocarbamate (PDTC, 12.5 microm). Corticosterone potentiated noradrenaline-induced melatonin and NAS production in a bell-shaped manner. The increase in NAS (12.9 +/- 2.7, n=6 versus 34.3 +/- 8.3 ng per pineal) and melatonin (16.3 +/- 2.0, n=6 versus 44.3 +/- 12.9 ng per pineal) content induced by 1 microm corticosterone was blocked by mifepristone, and mimicked by ALLN and PDTC. The presence of GRs was shown by [3H]-dexamethasone binding (0.30 +/- 0.09 pmol/mg protein) and corticosterone inhibition of NFkappaB nuclear translocation was demonstrated by electromobility shift assay. Therefore, corticosterone potentiates noradrenaline-induced melatonin and NAS production through GR inhibition of NFkappaB nuclear translocation. To the best of our knowledge, this is the first time that this relevant pathway for passive and acquired immune response is shown to modulate melatonin production in pineal gland.

Bone specific binding sites for 1,25(OH)2D3 in magnesium deficiency

It has been reported that some hypoparathyroid patients with magnesium deficiency showed altered responses to vitamin D treatment. In the same way, in vitro bone studies have demonstrated the existence of a decrease in the 1,25-dihydroxyvitamin D3-induced resorption in bone as a result of magnesium deficiency. These findings suggest some kind of alteration in the 1,25(OH)2D3 in bone in magnesium deficiency. In the present work, using a binding assay based on the 1,25(OH)2D3 and 3H-1,25(OH)2D3 competition for the hormone binding sites in rat calvaria homogenates, a significant decrease in the number of 1,25(OH)2D3 specific binding sites has been found in calvaria incubated in magnesium-deficient medium compared to magnesium-replete ones. Alterations in the hormone-receptor affinity were not found. These results suggest that an alteration in the 1,25(OH)2D3 action on magnesium-deficient bone could be due, at least in part, to a decrease in the number of available vitamin D receptors in bone cells.

Expression of Hex homeobox gene during skin development: Increase in epidermal cell proliferation by transfecting the Hex to the dermis

A number of homeobox genes have been found to be expressed in skin and its appendages, such as scale and feather, and appear to be candidates for the regulation of the development of these tissues. We report that the proline-rich divergent homeobox gene Hex is expressed during development of chick embryonic skin and its appendages (scale and feather). In situ hybridization analysis revealed that, during development of the skin, a transient expression of the Hex gene was observed. While the expression of Hex in the dermis was closely correlated with proliferation activity of epidermal basal cells, that in the epidermis was related to a suppression of epidermal differentiation. When dermal fibroblasts were transfected with Hex, stimulation of both DNA synthesis and proliferation of the epidermal cells followed by two-fold scale ridge elongation and increase in epidermal area was observed during culture of the skin, whereas epidemal keratinization was not affected. This is the first study to demonstrate that Hex is expressed during development of the skin and its appendages and that its expression in the dermal cells regulates epidermal cell proliferation through epithelial mesenchymal interaction.

Osteogenesis from cultured chick periostea has a specific requirement for chloride

Bone development, like embryonic development in general, depends on a particular internal electrical milieu. Ions are the carriers of currents that maintain this internal environment. In embryonic bone, chloride is a major carrier of such current. To explore the role chloride plays in embryonic bone development we performed several ion-removal experiments, using the chick periosteal osteogenesis (CPO) system as our model. We found that if chloride is reduced in the medium and replaced with a nontoxic anion, alkaline phosphatase (ALP) activity does not rise, nor does osteogenic development occur. However, acid phosphatase (AP) activity is not affected by level of chloride. Experiments using metabolic inhibitors showed that explants cultured in low chloride medium remain viable. Dose-response studies revealed that the response of ALP activity to chloride concentration is sigmoidal, with a [Cl-]0.5 of 45.9 mM. Reciprocal transfers of explants between complete and low chloride medium show that the rise in ALP activity depends on the length of time explants are cultured with chloride. In contrast, such transfer experiments show that osteogenesis requires chloride only during days 2-3 of culture.

Purinergic and noradrenergic cotransmission in the rat pineal gland

ATP is coreleased with noradrenaline in several noradrenergic synapses, and P2-like receptors were shown to be present in rat pineal glands. A new method of functional investigation was developed to assess the importance of both transmitters (noradrenaline and ATP) in eliciting the synthesis of melatonin and its precursor N'-acetyl-5-hydroxytryptamine (N'-acetyl-5-HT) through transmural electrical field stimulation of cultured pineal glands. Incubation with the beta-adrenoceptor antagonist propranolol (>10(-7) M) blocked almost completely the production of N'-acetyl-5-HT, whilst the P2 receptor antagonists pyridoxalphosphate-6 azophenyl-2',4'-disulfonic acid (PPADS, >3x10(-6) M) and suramin (>10(-6) M) blocked it partially. These findings indicate a physiologically relevant role for the purinergic cotransmission in this system.

THE EFFECT OF ANTISERUM, ALONE AND WITH HYDROCORTISONE, ON FOETAL MOUSE BONES IN CULTURE

1. The effects of normal rabbit serum and of rabbit antiserum to whole foetal mouse tissues, on the isolated limb bones of late foetal mice were studied in organ culture, and the influence of hydrocortisone on these effects was investigated. 2. Unheated normal serum caused slight loss of metachromatic material from the cartilage matrix, and some resorption of both cartilage and bone. 3. In unheated antiserum to foetal mouse tissues, the terminal cartilage was smaller and less metachromatic than in paired controls in normal serum, while osteoclasis was so intense that in many explants the bone had almost disappeared. The amount of necrosis varied with different batches of antiserum. 4. The changes produced by normal serum and antiserum could be largely prevented by heating the sera to 57 degrees C for 45 minutes. 5. The effects could also be inhibited by the addition of hydrocortisone to the unheated sera; as little as 0.1 microg hydrocortisone per ml of medium had a well marked protective action. 6. It is suggested that (a) unheated antiserum causes a release of lysosomal enzymes with consequent breakdown of intercellular material, (b) this release is due to an indirect action on the lysosome via an increased permeability of the cell membrane, (c) hydrocortisone does not affect the antigen-antibody reaction, but inhibits the autolytic changes that normally follow this reaction, possibly by stabilising both the lysosomal and cell membranes.

Inhibition by tunicamycin of mucin synthesis, not morphological changes, in epidermis during retinol-induced mucous metaplasia of chick embryonic cultured skin

BACKGROUND

Our previous studies have shown that epidermal mucous metaplasia of chick embryonic skin can be induced by culture in medium containing 20 microM retinol for only 8 hr and then in a chemically defined medium without retinol for 2 days and that retinol primarily affects the dermal cells, which then transform the epithelial cells into mucus-secreting cells.

METHODS

Tarsometatarsal skin of 13-day-old chick embryo was cultured with 20 microM retinol for 1 day and then without the vitamin but with 0.1 microgram/ml tunicamycin for 5 days. Effect of tunicamycin on epidermal mucous metaplasia was studied biochemically and morphologically.

RESULTS

Tunicamycin, which prevents the formation of N-glycans and inhibits maturation or morphological organization of various epithelial cells, irreversibly inhibited the synthesis of sulfated glycoproteins (O-glycans, mucin) in the epidermis only when applied to retinol-pretreated skin. Microvilli on the surface of the cells were well developed, but mucous granules surrounded by a limiting membrane were not observed in the upper cell layer of the epidermis, and many vesicles without electron-dense materials (mucin) and dilated rough endoplasmic reticulum were seen in the intermediate cell layers of the epidermis. When recombinants of 13-day-old normal epidermis and cultured dermis, which had been treated with retinol for 24 hr and with only tunicamycin for 2 days, were cultured without the antibiotic for 5 days, epidermal mucous metaplasia was induced.

CONCLUSION

These results suggest that tunicamycin did not prevent morphological changes induced by retinol but inhibited mucin synthesis by a direct action on the epidermis of retinol-pretreated skin. Because in some cell-line mucin precursors contain high mannose N-linked oligosaccharides side chains, tunicamycin may have inhibited mucin synthesis. Interaction between epidermal basal cells and retinol-pretreated dermal fibroblasts is prerequisite for epidermal mucous metaplasia. Thus, the present study suggests that N-linked protein glycosylation is not required for this interaction.

Bicarbonate dependence of ion current in damaged bone

The aim of this work was to characterize the ion current that enters mouse metatarsal bones following damage to the cortex. We assessed both the spatial distribution of this current and its dependence on the presence of bicarbonate in the medium. We used a voltage-sensitive probe system vibrating in two dimensions and recorded the signal as function of the position of the probe with respect to the site of damage and of ion substitutions in the medium. When the cortex was damaged (50 microm cylindrical hole penetrating into the marrow cavity), we recorded a steady state net inward electrical current directed toward the site of damage. In nonbicarbonate media, the density of the current was maximal near the center of the hole and ranged from 6 to 18 microA/cm2. As the probe was moved off the center of the hole, measured current density decreased in a manner consistent with the hypothesis that the source of the inward current is localized to the hole. After changing bicarbonate concentration in the medium from 0 to 42 mM, the current density nearly doubled, then decayed back to its original level exponentially over 35 minutes. When the diaphysis of living bone was left intact the current density was close to background level either in the presence or absence of bicarbonate in the medium. Damaged dead bone did not drive any current higher than background level. We conclude that the vibrating probe technique is a powerful tool to characterize ion currents in injured bone, helping to understand the physiology of bone-plasma interface and the bone healing processes. The current density transiently doubled upon addition of bicarbonate, indicating that this ion may carry the electrical current in damaged bone, probably by pump-leak mechanisms operating at the bone-plasma interface.

Immunocytochemical localization of the protein reactive to human beta-1, 4-galactosyltransferase antibodies during chick embryonic skin differentiation

BACKGROUND

beta-1, 4-Galactosyltransferase (GalTase) transfers galactose from UDP-galactose to terminal N-acetylglucosamine in glycoconjugates and is located both in the Golgi apparatus and in the plasma membrane. The cell surface GalTase is thought to be involved in cell-to-cell recognition and cell-to-extracellular matrix interaction.

METHODS

By the use of specific monoclonal antibodies against human GalTase, changes in cell surface localization of the protein reactive to the antibodies in chick embryonic skin during its differentiation in vivo and in vitro were detected immunohistochemically at both light- and electron microscopic levels. The distribution of glycoconjugates having terminal N-acetylglucosamine residues was detected by staining with succinylated wheat germ agglutinin (s-WGA).

RESULTS

Under the light microscope, intense immunostaining was observed in the keratinized epidermis, particularly in the intermediate layer. Marked changes in the localization of the staining were observed in vitamin A-induced mucus-secreting skin, in which keratinization was suppressed. The localization of the immunostaining was in parallel with that of glycoconjugates having terminal N-acetylglucosamine residues. Immunoelectron microscopically the immunostaining was located on the cell surface and in the intercellular space of the desmosomes in the intermediate cells of the keratinized epidermis. However, the staining was not present on the cell surface but was detected on the limiting membrane of the mucous granules, in the mucous metaplastic epidermis. In contrast, the staining was always found in the Golgi apparatus in all of the cells.

CONCLUSIONS

These results suggest that the protein reactive to human GalTase antibody may be involved in chick epidermal differentiation.

Characterization of inhibitory effects of suspected periodontopathogens on osteogenesis in vitro

By using an in vitro bone-forming culture system, the chick periosteal osteogenesis (CPO) model, the direct effects on osteogenesis of sonicated extracts derived from oral bacteria were examined. Both extracts from bacterial species having strong associations with periodontal diseases (Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Prevotella intermedia, hereinafter referred to as suspected periodontopathogens) and extracts from species not correlated with periodontal disease (Streptococcus sanguis, Veillonella atypica, and Prevotella denticola, hereinafter referred to as nonpathogenic bacteria) were tested. All bacterial cultures were grown under standard anaerobic culture conditions. Sonicated bacterial extracts were prepared from the bacterial pellet. These were added in various proportions to the CPO cultures. Parameters of osteogenesis, including alkaline phosphatase activity, calcium and P(i) accumulation, and collagen synthesis, were measured in 6-day-old cultures. Compared with controls grown in the absence of bacterial products, osteogenesis was inhibited significantly in cultures treated with extracts derived from the suspected periodontopathogens. No osteogenic inhibition was observed in cultures treated with extracts from the nonpathogenic bacteria. These results suggest that the ability to inhibit osteogenesis in vitro may be a pathogenic property shared by a limited group of species. Further characterization of the P. gingivalis extracts revealed that both proteinaceous and nonproteinaceous products, including lipopolysaccharide, were able to inhibit osteogenesis. P. gingivalis extract-mediated inhibition of osteogenesis in CPO cultures was blocked by indomethacin, implicating prostaglandins in the regulation of the bacterial effects. The bacterial extracts had either reversible or irreversible inhibitory effects on osteogenesis when added after differentiation or before/during differentiation of bone cells, respectively.

Development of a suspension organ culture of the fetal rat palate

On the basis of an already established suspension organ culture system of mouse palate anlagen, we developed a corresponding culture system for rat palate anlagen. In order to optimize the culture results we systematically studied the influence of main "culture conditions" such as dissection technique, rotation speed, gassing schedule, and developmental stage at the onset of culture for mice and rat palate anlagen. This system allows culturing rat palate anlagen from day 15 of gestation to day 18 + 8 h (80 h) under serum- and antibiotic-free conditions using a chemically defined medium, resulting in 90% fused palates. The explants, containing the maxillary vault and the palatal shelves, were cultured in siliconized culture flasks at a rotation speed of 12 rpm and a temperature of 37 degrees C (Table 1).

Changes in expression of two endogenous beta-galactoside-binding isolectins in the dermis of chick embryonic skin during development in ovo and in vitro

In order to elucidate the roles of metal-independent animal lectins, we systematically investigated changes in expression of 2 kinds of beta-galactoside-binding isolectins (MW 14 and 16 kDa) in the dermis of chick embryonic tarsometatarsal skin during the course of development. These lectins were immunohistochemically located at different stages of development both in ovo and in vitro by light and electron microscopy. Light-microscopic observation showed that while positive staining for the 14-kDa lectin was weak at days 8 and 10 it became intense after day 13. In contrast, staining for the 16-kDa lectin was intense at days 8, 10, and 13, but it became weak after day 17 when keratinization of the epidermis was completed. Immuno-electron-microscopic observation revealed that both the 14 and 16-kDa lectins were located on the basement membrane, in the extracellular matrix, and in both the cytoplasm and the nucleus of dermal fibroblasts. Distribution of the 2 isolectins was also examined in cultured skin explants in vitro. The results were almost the same as those obtained in ovo when the skin explant was keratinized in the presence of hydrocortisone. However, in the skin explant where keratinization was prevented and mucous metaplasia was induced by the addition of vitamin A, the distribution of the 14-kDa lectin in the epidermis was significantly affected. These results indicate that (1) the expression of the 2 isolectins is differently regulated in both the dermis and epidermis, (2) the 16-kDa lectin is involved in the early stage of the formation of the dermis and the basement membrane and is replaced by the 14-kDa lectin as keratinization of the epidermis occurs, and (3) the expression of the 2 isolectins in the dermis is not significantly affected by the induction of mucous metaplasia, in contrast to their drastic changes in the epidermis.

In vitro effect of KCA-098, a derivative of coumestrol, on bone resorption of fetal rat femurs

The effects of 3,9-bis(N,N-dimethylcarbamoyloxy)-5H-benzofuro[3,2-c]quinoli ne-6-one (KCA-098), a derivative of coumestrol, on bone resorption was studied in organ cultures of 20-day fetal rat femora. KCA-098 increased the length, dry weight, and calcium and phosphorus contents of parathyroid hormone (PTH)-treated fetal rat femur. As PTH significantly reduced the calcium and phosphorus contents of the femora, probably by stimulating bone resorption, KCA-098 seems to inhibit bone resorption. In fact, KCA-098 inhibited the PTH-induced release of 45Ca from pre-labeled fetal rat femora into the medium in organ culture. Coumestrol also inhibited the release of 45Ca from bone into the medium. However, KCA-098 did not increase the uterine weight of ovariectomized rats, whereas coumestrol did so. Thus KCA-098 is a unique, new inhibitor of bone resorption that has no estrogenic activity.

Effect of Pasteurella multocida toxin on bone resorption in vitro

Pasteurella multocida toxin (PMT), which is the primary etiologic factor in the pathogenesis of progressive atrophic rhinitis in pigs, was found to stimulate bone resorption in vitro. This stimulation was observed both in cultures of murine calvaria by measuring the release of calcium and of the lysosomal enzyme beta-glucuronidase and in murine long bone cultures by measuring the release of calcium. Both systems showed the same dose response curve, with the maximal effect at a concentration of 5 ng/ml. The effect on calvaria was studied in more detail. PMT increased bone resorption 24 h after its addition and always had to be present to express an effect. Calcitonin was able to inhibit this increase of resorption completely, and inhibitors of prostaglandin synthesis suppressed it partially. Although the data show an effect of PMT on bone tissue, the results do not exclude an action on cells in the nasal cavity, which could indirectly stimulate bone resorption.

Changes in expression of the endogenous beta-galactoside-binding 14-kDa lectin of chick embryonic skin during epidermal differentiation

Changes in the expression pattern of the gene for the endogenous beta-galactoside-binding 14-kDa lectin of chick embryo were examined immunohistochemically during epidermal differentiation in vivo and in vitro with special reference to detailed localization of the 14-kDa lectin. The gene expression was visualized by the HRP-staining method following in situ hybridization, in which sulfonated cDNA was employed as a probe. The 14-kDa lectin gene expression (mRNA) was detected mainly in the intermediate layer of the epidermis: it was faint in 13-day-old embryos, gradually increased in intensity during epidermal differentiation, and became intensely positive in 17-day-old embryo. The expression of the gene in skin explants was suppressed by vitamin A, which induces mucous metaplasia of the epidermis in vitro. The anti-14-kDa lectin reaction was positive mainly in the intermediate layer of the differentiating epidermis, coinciding chronologically with expression of the gene at the light microscopic level. Immunoelectron microscopy revealed that the positive reaction was primarily localized in desmosomes, in tonofilament bundles anchored to the desmosomes, along the outer surface of the plasma membrane, and in the intercellular space. Essentially the same staining pattern was observed in differentiating epidermis in vitro. The positive reaction was markedly reduced in the epidermis in which differentiation had been suppressed in vitro by the addition of vitamin A.

Reconstruction of basement membrane in recombinants of epidermis and dermis of chick embryonic skin in vitro: an electron microscopic study

The tarsometatarsal skin from 13-day-old chick embryos was treated with EDTA and/or Dispase to separate it into epidermis and dermis, and the basal lamina was removed. The isolated epidermis and dermis were then recombined and cultured on Millipore filters in a chemically defined medium (BGJb). Beginning at 3-4 days after recombination, short fragments of new basal lamina and subbasal dense plaque were formed along the epidermal basal cell outer surface immediately subjacent to hemidesmosomes. After 6-8 days of culture, fragments of the basal lamina started to fuse together and the lamina became progressively continuous. At the same time, anchoring fibrils were formed to attach to the basal lamina. The hemidesmosome formation preceded the basement membrane formation. When normal embryonic epidermis was recombined with retinol-pretreated dermis and cultured for 7 days in BGJb, short fragments of the basal lamina, the subbasal dense plaque, and anchoring fibrils were formed, but the basement membrane remained discontinuous with many interruptions in the interspace between hemidesmosomes. These results demonstrate that pretreatment of dermis with retinol causes the changes noted in the basement membrane.

Short term retinol treatment in vitro induces stable transdifferentiation of chick epidermal cells into mucus-secreting cells

Epidermal mucous metaplasia of cultured skin can be induced by treatment with excess retinol for several days (Fell 1957). In the induction of mucous metaplasia, retinol primarily affects the dermal cells and retinol-pretreated dermis can alter epidermal differentiation towards secretory epithelium (Obinata et al. 1987). In this work, we found that mucous metaplasia could be induced by culturing 13-day-old chick embryonic tarsometatarsal skin in medium containing retinol (20 μM) for only 8-24 h, followed by culture in a chemically defined medium (BGJb) without retinol or serum for 6 days. The application of cycloheximide together with retinol during the first 8 h of culture inhibited epidermal mucous metaplasia during subsequent culture for 6 days in BGJb, indicating that induction of a signal(s) in the dermis by excess retinol requires protein synthesis. However, the presence of 20 nM hydrocortisone (Takata et al. 1981) throughout the culture period did not inhibit retinol-induced epidermal mucous metaplasia of the epidermis. This indicates that a brief treatment of the skin with excess retinol determines the direction of epithelial differentiation toward secretory epithelium; this is a simpler in vitro system for the induction of epidermal mucous metaplasia than those established before.

A serum substitute promotes osteoblast-like phenotypic expression in cultured cells from chick calvariae

The effects of medium supplements were tested on embryonic chick calvarial cells in culture. Isolates were divided among four treatment groups: Nu-Serum, chicken serum, fetal bovine serum, or calf serum. Expression of the osteoblastic phenotype was assessed by cell morphology, DNA content, [3H]thymidine incorporation, lactate production, cellular and medium alkaline phosphatase activities, and collagen synthesis. Cells grown in Nu-Serum demonstrated increased alkaline phosphatase activity and a six-fold higher rate of collagen synthesis compared to chicken serum. These cells displayed a polygonal profile, abundant rough endoplasmic reticulum, Golgi apparati, and elaborated an extensive matrix of banded collagen which was well mineralized by day 10 of culture. Although highly mitogenic, chicken serum promoted a more fibroblastoid morphology. Compared to the sera tested, Nu-Serum preferentially promoted the osteoblast-like phenotype in chick calvarial cells in culture.

The activity of 2,5-oligoadenylate synthetase, an interferon-induced enzyme, is coupled to the differentiation state of mouse condylar cartilage

The enzyme 2,5-oligoadenylate synthetase (2-5A synthetase) is associated with the interferon system, with special reference to the differentiation process of various cell types. The present study investigated whether 2-5A synthetase is also involved in the differentiation of neocartilage in perinatal mice. The cartilage of the mandibular condyle, a secondary type of cartilage, develops relatively late in prenatal life; and consequently it was possible to obtain a relatively embryonic cartilage at a developmental stage that could be manipulated enzymatically, in order to separate and thereby obtain its undifferentiated, proliferative portion along with its more mature fraction. Immunohistochemical studies using antibodies against type I and type II collagen and cartilage-specific proteoglycans could have determined the differentiation status of various portions of the developing condyle. However, the above methodology lacks the necessary precision and accuracy to indicate subtle changes in cellular differentiation. It became evident that the activity of 2-5A synthetase was indeed different in cellular compartments that were at different stages of differentiation. In the neonatal condyle the highest level of activity was encountered in proliferating and as yet undifferentiated prechondrocytes, whereas fully differentiated chondrocytes showed a marked decrease in the activity of this enzyme.

A suitable culture medium for ossification of embryonic chick femur in organ culture

To establish a culture medium which allows ossification in organ culture, 9-day-old embryonic chick femurs were cultured in variously supplemented BGJb-HW2 media. Changes of Ca and Pi concentrations in the BGJb-HW2 medium or the 10% addition of chick embryo extract (CEE) did not induce ossification. Furthermore, combinations of the 10% CEE with a high Ca x Pi product or with 5 mM beta-glycerophosphate (beta-GP) or with 10% horse serum plus a high Ca x Pi product often caused pathological abnormalities in the periosteum. On the other hand, BGJb-HW2 medium supplemented with 5 mM beta-GP induced development of ossification. The Ca content of femurs and the diaphysial hydroxyproline content were markedly increased. Histological observation showed a formation of a thick and active periosteum, numerous osteoblastic cells, a sufficient amount of osteoid tissue and well developed calcified trabeculae without any pathological changes. Thus, the organ culture system using this medium was considered to be an appropriate one for studies on osteogenesis in vitro.

Effect of adriamycin on hamster molar tooth development in vitro: 1. Morphological changes

The effect of adriamycin (1 mg/liter) on the development of the golden hamster 3-day-old second maxillary molars (M2) was investigated in vitro. Exposure of the molars to 1 mg/liter adriamycin during the first 2 hours of culture produced smaller teeth 3-7 days later, as determined by measurements of dry weights and by histological observations. Higher doses caused severe necrosis. The more differentiated pulp fibroblasts showed osteodentin formation 3 days after treatment with adriamycin (1 mg/liter), while the more immature ones underwent necrosis. The phenotypic changes brought on by the drug were permanent, and osteodentin continued to be formed throughout the course of this study. In addition the cervical loop region was inhibited from growing, while the production of the matrices of enamel and dentin appeared to be increased at 3 and 5 days after treatment. Electron microscopy of the forming osteodentin matrix revealed a random arrangement of banded collagen fibers during the early stage of osteodentin formation. As more matrix was formed, the collagen became quite compact and appeared quite similar to dentin. Finally, matrix vesicles were found among the collagenous matrix that was not yet mineralized. With the exception of the increased production of enamel and dentin, these in vitro results confirmed those earlier in vivo studies on the effect of adriamycin on rat incisor tooth.

Evidence that fluoride-stimulated 3[H]-thymidine incorporation in embryonic chick calvarial cell cultures is dependent on the presence of a bone cell mitogen, sensitive to changes in the phosphate concentration, and modulated by systemic skeletal effectors

In previous studies we have shown that clinically effective concentrations of fluoride (5 to 30 mumol/L) could also have direct effects in vitro on skeletal tissues to increase embryonic chick bone formation and bone cell proliferation (3[H]-thymidine incorporation into DNA). From these observations, we hypothesized that fluoride-stimulated bone formation might be mediated by a direct effect of fluoride to increase bone cell proliferation. The current studies were intended to investigate the mechanism of fluoride-stimulated 3[H]-thymidine incorporation, in chick calvarial cell cultures, by assessing mitogenic interactions between fluoride and inorganic phosphate, bone-derived growth factors, and systemic skeletal effectors. With respect to fluoride-phosphate interactions, the results of our studies indicate that the effect of fluoride was dependent on the phosphate concentration in the medium. Fluoride did not increase 3[H]-thymidine incorporation in BGJb medium containing 1 mmol/L (total) phosphate; but, in 1.6 mmol/L phosphate medium, fluoride caused a dose-dependent increase in 3[H]-thymidine incorporation, between 1 and 20 mumol/L (P less than .001). The action of fluoride was also dependent on the presence of a bone cell mitogen. Fluoride increased 3[H]-thymidine incorporation when added to calvarial cell cultures in the cell-conditioned medium, but had no effect in unconditioned (ie, fresh) medium. The action of fluoride could be restored by adding an exogenous growth factor (ie, concentrated cell-conditioned medium, bone-derived growth factors, or a systemic bone cell mitogen) to the unconditioned culture medium, P less than .05 for each effector.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term storage of freshly harvested bone

An in vitro study was designed to test effects of various graft storage media on glucose metabolism and collagen synthesis of embryonic chick tibiae, using these variables as indices of bone cell viability. Normal saline solution, distilled water, and 5% dextrose in lactated Ringer's solution were evaluated after a 5-hour incubation and again after a 3-day recovery period in a complete culture medium. The study suggests that bone grafts may be stored in normal saline solution or 5% dextrose in lactated Ringer's solution for up to 5 hours. Normal saline solution is recommended because of fewer deleterious effects. Distilled water should not be used as a storage medium for bone grafts.

Insulin and glucose regulation of glycogen synthase in rat calvarial osteoblastlike cells

Insulin has been shown to stimulate collagen, noncollagen protein and nucleic acid synthesis in bone cells in vitro. However, the effects of insulin on intermediary carbohydrate metabolism in osteoblasts, and in particular on the key regulatory enzyme glycogen synthase, have not been directly examined. Accordingly, we developed a microassay for glycogen synthase (GS) to examine insulin and glucose regulation of this enzyme in cultured osteoblastlike cells. In osteoblast-enriched rat calvarial bone explants incubated for 24 hours in 5 mM glucose, insulin (0.1-100 nM) produced a dose-related stimulation of GSa (glucose-6-phosphate independent GS activity). The insulin-stimulated increase in GSa ranged from a 30% increase in the presence of 0.1 nM insulin to a 163% increase produced by 100 nM insulin, both significant at P less than 0.01. In contrast, GSb (glucose-6-phosphate dependent GS activity) was significantly increased only at a supraphysiologic insulin concentration (100 nM). The GS activity ratio (GSa/GSb) increased with insulin concentration from 0.1-100 nM. Basal values for GSa and GSb activity did not differ between explants incubated in 5mM or 15 mM glucose for 24 hours. However, incubation in the presence of 15 mM glucose blunted the insulin-stimulated increase in GSa activity, with 100 nM insulin producing only a 75% increase in GSa activity. In contrast, maximal insulin-stimulated GSb levels were not affected by high glucose medium. In explants incubated in glucose-free medium, basal GSa activity was significantly greater than in the presence of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

A technique for the in vitro incubation of deer antler tissue

1. A procedure for the in vitro incubation of velvet deer antler tissue was developed. Biopsy samples were collected in June with a trephine from 2 adult white-tailed deer and incubated in modified BGJb medium up to 48 hr. Calcium (Ca) and hydroxyproline (OH-proline) concentrations in the tissue were determined. 2. A significant increase (P less than 0.05) in Ca was exhibited at 4 and 8 hr of incubation, and, after replenishment of media, at 48 hr. 3. Hydroxyproline concentrations continued to rise throughout the duration of the incubation period and were significantly higher than controls (P less than 0.05) at 16, 24, and 48 hr. 4. Results suggest antler tissue can be incubated in vitro with the protocol described, although length of incubation may vary with parameter measured.

Localization of cellular calcium in differentiating ameloblasts and its relationship to the early mineralization process in mantle dentin and enamel in hamster tooth germs in vitro

The relationship between the distribution of calcium in the cells of the enamel organ and the mineralization process in mantle dentin and enamel was investigated at the ultrastructural level in cultured hamster second maxillary molar tooth germs explanted before the onset of mineralization (bell stage). During the early stages of pre-odontoblast and pre-ameloblast differentiation, pyroantimcnate (PA) reaction product for calcium was observed only in the nuclei. However, an abrupt increase in PA reaction product appeared in the apical cytoplasm of both the pre-odontoblasts and pre-ameloblasts prior to the onset of mantle dentin mineralization. In the pre-dentin, the PA reaction product was localized mainly on the striated collagen fibers. The PA reaction product in the apical poles of these cells increased concomitantly with increasing mantle dentin mineralization. The amounts of PA reaction product along the plasma membranes and in the cytoplasm decreased in the direction of the basal (stratum intermedium) pole. The highest PA activity in the cytoplasmic side of the plasma membranes of the ameloblasts was found during the secretory phase of amelogenesis. However, in the area around the tips of the Tomes' processes, membrane-associated and cytoplasmic PA activity was low or absent but gradually increased toward the ameloblast cell body, an indication of the presence of a calcium gradient in the processes.

These results indicate that in vitro: (1) both odontoblasts and (pre)-ameloblasts are involved in the calcium acquisition necessary for the initial stages of mantle dentin mineralization; (2) in ameloblasts, there is a calcium gradient in the direction of the mineralization front from the earliest stages of mantle dentin mineralization onward; (3) enamel matrix does not seem to be involved in calcium translocation to the enamel mineralization front; (4) the Tomes' processes seem to regulate transmembrane calcium transport to the mineralization front; and (5) the distribution of calcium in the enamel organ is comparable with that found in vivo.

Light and transmission electron microscopy of the effects of calcium, magnesium and phosphate on dentine and enamel formed by rat molars in vitro

The effect of addition of eight different combinations of Ca, Mg and P supplements (control, Ca, Mg, P, CaMg, CaP, PMg and CaMgP) on three-day-old rat maxillary second molars, explanted at the premineralizing stage and cultured for two weeks, was studied. Light-microscopy sections, cut parallel to the occlusal plane, were divided into four sectors and given a score according to an ordinal scale for dentine and enamel depending on the regularity of these matrices. An analysis of variance on these scores revealed a significant favourable effect of Mg, CaMg and CaMgP and an adverse effect of Ca on enamel. A favourable effect on dentine regularity was obtained after addition of Ca or Mg. Ultrastructurally, enamel changes such as amorphous enamel matrix, voids and disturbance in rod-interrod pattern were seen after addition of Ca, P, CaP. Thin enamel with less tight packing of crystals was observed after CaMg addition. A thick layer of enamel with highly-organized rod-interrod pattern was seen with Mg, PMg and CaMgP addition. It is suggested that Mg plays an important role in the interaction with Ca and P for the harmonious development of enamel and dentine in vitro.

Effect of alkaline-phosphatase inhibition by 1-p-bromotetramisole on the formation of trichloroacetic acid-[32P]-insoluble phosphate from inorganic [32P]-phosphate and [32P]-pyrophosphate in non-mineralizing and mineralizing hamster molar tooth-germs in vitro

In culture, 1-p-bromotetramisole (pBTM), a specific inhibitor of alkaline phosphatase, significantly inhibited the formation of trichloroacetic acid (TCA)-insoluble [32P]-phosphate from inorganic [32P]-phosphate in the proliferating non-mineralizing second (M2) maxillary molar germs but had no effect in the actively mineralizing first (M1) germs. Addition of 10(-5) M inorganic pyrophosphate in the culture medium with a [32P]-phosphate label increased the inhibition of the formation of TCA-insoluble [32P]-phosphate in the M2. pBTM almost completely inhibited the formation of TCA-insoluble [32P]-phosphate from inorganic [32P]-pyrophosphate in the non-mineralizing M2. In the actively mineralizing M1, the compound significantly inhibited but did not abolish the formation of TCA-insoluble phosphate. These results confirm earlier biochemical findings that alkaline phosphatase possesses a pyrophosphatase activity probably related to the turnover of phosphorylated macromolecules necessary for cell differentiation and proliferation.

Ultrastructure of in-vitro recovery of mineralization capacity of fluorotic enamel matrix in hamster tooth germs pre-exposed to fluoride in organ culture during the secretory phase of amelogenesis

The recovery of mineralization capacity of fluorotic enamel matrix was investigated in 3-day-old hamster first molar tooth germs already pre-exposed in organ culture to 10 parts/10(6) F- for 24 h during the secretory phase. The germs were then cultured for another 24 h in a fresh medium without F-. The unmineralized fluorotic enamel matrix secreted in vitro eventually mineralized in the absence of F- but the orientation of the crystals compared to those in the fluorotic enamel was disturbed, especially in the younger regions of the enamel nearest cervical-loop in which the underlaying fluorotic enamel was most hypermineralized; but least disturbed in the more mature parts of the enamel organ in which the fluorotic enamel was less hypermineralized. The subsequent culture in F(-)-free medium did not abolish or reduce the degree of hypermineralization induced by F- treatment during the initial 24 h of culture. It seems that in vitro the inhibitory effect of F- on enamel matrix mineralization during the secretory phase is completely reversible when the ion is removed from the matrix environment, i.e. F(-)-induced synthesis and secretion of defective enamel matrix is not the cause of the lack of matrix mineralization. The F(-)-induced hypermineralization seems to be irreversible.

Growth and growth pressure of mandibular condylar and some primary cartilages of the rat in vitro

To compare the in vitro development of the secondary cartilage of the mandibular condyle with that of primary cartilages, several cartilaginous explants derived from 4-day-old rats were cultured in a serum-free culture system. The following cartilages were used: the mandibular condylar cartilage, the distal epiphyseal cartilage (including the growth plate) of the third metatarsal, a fragment of costal cartilage (including the osteochondral junction) of the fourth rib, the spheno-occipital synchondrosis and the chondroepiphysis of the femoral head. In addition, with a specially designed, in vitro pressure registration system, the maximal growth pressures for each of the explants, except the femoral head, were determined. The results show an independent growth potential for the primary cartilages of the epiphyseal and costal growth plates with a maximal growth pressure of 9.5 and 7.8 g/mm2, respectively. The primary cartilage of the spheno-occipital synchondrosis, on the other hand, although it possesses an independent growth potential, could exert a maximum growth pressure of only 1.5 g/mm2. The secondary cartilage of the mandibular condyle showed a limited intrinsic growth potential, as well as a low maximal growth pressure (2.6 g/mm2). If calculated per dividing and/or matrix synthesizing cell (cells mainly responsible for the cartilage growth), the cells of the condylar cartilage showed the least growth potency (0.08 mg/cell in comparison to 1.9, 1.5 and 0.3 for epiphyseal, costal, and synchondroseal cartilages, respectively.

Ultrastructural study of fluoride-induced in-vitro hypermineralization of enamel in hamster tooth germs explanted during the secretory phase of amelogenesis

The effects of fluoride (5, 10 and 20 parts/10(6) F-) were studied in vitro with light and electron microscopy in 5-day-old hamster maxillary second molar tooth germs explanted when most of the ameloblasts are in the secretory phase, and cultured for 24 h in the presence of F-. F- at all doses investigated induced hypermineralization of that enamel which had been secreted in vivo just prior to exposure to F-. The most intense hypermineralization was in the aprismatic enamel near the cervical loop region, where the in-vivo enamel layer was thinnest and gradually decreased (but was not abolished) with the increasing thickness of in-vivo formed enamel in the more mature parts of the enamel organ. The fluoride-induced hypermineralization in the aprismatic enamel layer did not stain at all with dilute toluidine blue solution and was therefore indistinguishable from the underlying dentine in light micrographs. The hypermineralization was due to growth in thickness of the enamel crystals, which in the aprismatic enamel layer resulted in a lateral fusion of all the enamel crystals. Thus fluoride administered during the secretory phase of enamel formation decontrols or even abolishes enamel crystal growth in length and promotes crystal growth in thickness so producing the hypermineralization of the pre-fluoride enamel. Enamel matrix secreted in the presence of fluoride did not mineralize.

Utilization and formation of amino acids by chicken epiphyseal chondrocytes: comparative studies with cultured cells and native cartilage tissue

Utilization and production of amino acids by primary cultures of chicken growth plate epiphyseal chondrocytes grown in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum were investigated in both short-term (6-72 h) and long-term (3-24 day) cultures. Comparative studies were made on levels of free amino acids in chicken blood plasma and serum, and in extracellular fluids from different regions of growth plate cartilage and from two types of muscle. Chondrocytes rapidly consumed glutamine from the medium, and to lesser extents, various other amino acids. In contrast, free ammonia, alanine, glycine, glutamate, proline, and aspartate were released into the medium. The utilization of certain amino acids changed, depending on the stage of culture. Initially glutamate was released into the medium but after confluency was consumed. Conversely, histidine, lysine, and phenylalanine were initially utilized but later were released into the medium. Levels of total free amino acids in extracellular fluids of cartilage and muscle were higher than those in plasma and serum, while in cartilage the levels increased progressively from the resting to the hypertrophic zones. In these sequential regions certain amino acids increased proportionally, whereas others decreased. These interrelationships generally correlated closely with metabolism of amino acids by the cultured chondrocytes. They indicate that significant differences in amino acid metabolism exist between tissue areas and are reflected in the extracellular fluid composition. Accordingly, adjustment of specific amino acids may optimize culture conditions, enabling more normal phenotypic expression in vitro.

Vitamin A and bone formation. Effect of an excess of retinol on bone collagen synthesis in vitro

The influence of an excess of retinol on bone formation was studied by using cultures of embryonic-chick calvaria. Retinol decreased collagen synthesis in a dose-dependent manner, non-collagenous protein synthesis being relatively unaffected. Collagen synthesis was significantly inhibited after 24 h of culture with retinol and was progressively decreased, compared with control cultures containing no retinol, as the period of culture was increased. The effect of retinol on collagen synthesis could be reversed by incubation of calvaria for further periods in retinol-free medium. Incorporation of [3H]thymidine and [3H]uridine into DNA and RNA respectively was not altered by culturing calvaria with retinol for 22 h. These latter findings, and the selectivity for collagen synthesis, all suggested that the effect observed was not a cell-toxicity phenomenon. The effect of retinol on collagen synthesis by chick calvarial osteoblasts was probably direct and not mediated by osteoclasts, since a negligible number of the latter cells is present in chick calvaria. In cultures of neonatal murine calvaria, which contain many osteoclasts, retinol similarly inhibited synthesis of collagen, but not of non-collagenous protein; the concentrations of retinol necessary to produce the response were similar to those required to stimulate bone resorption in vitro.

Changes in morphology and cell proliferation during vitamin A-induced mucous metaplasia of developing chick scale cultured in vitro

Throughout the process of vitamin A (V-A)-induced mucous metaplasia of the scale epidermis of a 12-day chick embryo, changes in the activities of cell proliferation were investigated in reference to morphological changes. In both the control and V-A cultures after 5 days, a dynamic steady state was established among the stratified layers which differentiated into keratinizing epidermis during the first 7 days. In the control, cell proliferates within only the basal layer and the cell cycle time, except Tg2, increased during 30 days of culture. In the V-A culture, this tendency was reversed in each parameter between day 10 and day 13, when symptoms of mucous metaplasia became morphologically prominent. On day 13 in the V-A culture, superficial cornified cell layers were sloughed off as whole sheets and concurrently DNA synthesis was reactivated throughout the entire cell layers of the epithelium. The correlation between two of five cell cycle times (Tgc, Tg1, Ts, Tg2, Tm) was statistically treated as linear regression lines and gave highly significant coefficients in every case. The regression coefficients between Ts and Tgc and Ts and Tg1 in V-A culture are significantly (P less than 0.01) smaller than those in the control. It was found that V-A induced sequential alterations in mucous metaplasia with respect both to morphology and proliferation in the epidermis of the chick embryo.

Effect of purified growth factors on rabbit articular chondrocytes in monolayer culture. I. Dna synthesis

The ability of purified growth factors, insulin, ascorbate, and several other compounds to stimulate DNA synthesis by rabbit articular chondrocytes was studied in monolayer culture. Platelet-derived growth factor (1 U/ml), pituitary fibroblast growth factor (1-100 ng/ml), and epidermal growth factor (1-50 ng/ml) were stimulatory in a basal medium supplemented with 1% heat-inactivated fetal bovine serum. Insulin, 1-50 micrograms/ml, has small growth-promoting effects but acted synergistically with platelet-derived, pituitary fibroblast, and epidermal growth factors. Increasing concentrations of serum up to 10% enhanced the growth-promoting action of the purified factors, but not of insulin. There were indications of cooperation between insulin and bovine serum albumin and dexamethasone. Ascorbate (0.2 mM) reduced or had little growth-promoting action in the basal medium. At 5 and 10% serum concentrations, however, ascorbate promoted DNA synthesis as effectively as the purified growth factors. No significant stimulatory effect was shown by transferrin, thrombin, L-glutamine, putrescine, selenous acid, dexamethasone, 7S nerve growth factor, or multiplication-stimulating activity.

Autoradiographic visualization of glycoproteins and glycosaminoglycans in the epithelio-mesenchymal interface of developing mouse tooth germ

The turnover of basement membrane macromolecules during tooth morphogenesis and odontoblast differentiation was examined by light microscopic autoradiography using 3H-fucose, 35S-sulfate and 3H-glucosamine. Marked incorporation into the basement membrane was found throughout the progressive development. Pulse-chase experiments and prelabeling of tissue components indicated that glycoproteins and glycosaminoglycans in the dental basement membrane are mainly derived from the enamel epithelium. During odontoblast differentiation, incorporation was increased at the epitheliomesenchymal interface at the site of differentiating mesenchymal cells. From these sites the label also disappeared rapidly. This suggests that the active remodeling of extracellular matrix is related to odontoblast differentiation.