Chondroitin sulfates in developing mouse tooth germs. An immunohistochemical study with monoclonal antibodies against chondroitin-4 and chondroitin-6 sulfates

The inhibition of glycosaminoglycan incorporation influences the cell proliferation and cytodifferentiation in cultured embryonic mouse molars

The extracellular matrix (ECM) contains a variety of complex macromolecules including proteoglycans (PGs) and glycosaminoglycans (GAGs). PG consists of a protein core with covalently attached carbohydrate side chains called GAGs. Several PGs, including versican, biglycan, decorin and syndecan are involved in odontogenesis while the role of GAGs in those PGs in this process remains unclarified. The purpose of this study was to investigate the influence of GAGs on tooth development. The mandibular first molars at early bell stage were cultivated with or without 4-methylumbelliferyl-β-D-xyloside (Xyl-MU). The cultured tooth germs were metabolically labelled with [³⁵S] Na₂SO₄, then PGs in tooth germs and cultured medium were extracted separately and analyzed by gel filtration. Morphological changes were evaluated on days 2, 4, 6, and histological changes were examined by hematoxylin-eosin (HE) staining and transmission electron microscope (TEM). Related proteins and genes of cytodifferentiation were further examined by immunohistochemistry (IHC) and quantitive real-time PCR (qPCR) respectively. Meanwhile, BrdU incorporation assay was used to explore the effect of Xyl-MU on the cell proliferation of cultured tooth germs. The results demonstrated that the incorporation of GAGs to PGs in cultured tooth germs was heavily inhibited by Xyl-MU. Accompanied by the inhibition of GAGs incorporation, Xyl-MU altered tooth morphogenesis and delayed the differentiation of ameloblasts and odontoblasts. Proliferation of inner enamel epithelium (IEE) was also inhibited. Therefore, we draw a conclusion that the inhibition of GAGs incorporation influences the cell proliferation and cytodifferentiation in cultured embryonic mouse molars.

Brain ageing changes proteoglycan sulfation, rendering perineuronal nets more inhibitory

Chondroitin sulfate (CS) proteoglycans in perineuronal nets (PNNs) from the central nervous system (CNS) are involved in the control of plasticity and memory. Removing PNNs reactivates plasticity and restores memory in models of Alzheimer’s disease and ageing. Their actions depend on the glycosaminoglycan (GAG) chains of CS proteoglycans, which are mainly sulfated in the 4 (C4S) or 6 (C6S) positions. While C4S is inhibitory, C6S is more permissive to axon growth, regeneration and plasticity. C6S decreases during critical period closure. We asked whether there is a late change in CS-GAG sulfation associated with memory loss in aged rats. Immunohistochemistry revealed a progressive increase in C4S and decrease in C6S from 3 to 18 months. GAGs extracted from brain PNNs showed a large reduction in C6S at 12 and 18 months, increasing the C4S/C6S ratio. There was no significant change in mRNA levels of the chondroitin sulfotransferases. PNN GAGs were more inhibitory to axon growth than those from the diffuse extracellular matrix. The 18-month PNN GAGs were more inhibitory than 3-month PNN GAGs. We suggest that the change in PNN GAG sulfation in aged brains renders the PNNs more inhibitory, which lead to a decrease in plasticity and adversely affect memory.

Expression, localisation and synthesis of versican by the enamel organ of developing mouse molar tooth germ: an in vivo and in vitro study

OBJECTIVE

Versican is a large, aggregating chondroitin sulphate proteoglycan. In dental tissue, versican expression occurs primarily in mesenchymal tissue but rarely in epithelial tissue. We investigated the expression, localisation and synthesis of versican in the enamel organ of the developing tooth germ.

DESIGN

To elucidate versican localisation in vivo, in situ hybridisation and immunohistochemistry were conducted in foetal ICR mice at E11.5-E18.5. Epithelium and mesenchyme from the lower first molars at E16.0 were enzymatically separated and versican mRNA expression was investigated by semi-quantitative RT-PCR. Organ culture of the separated samples combined with metabolic labelling with [(35)S], followed by gel filtration, was performed to analyse secreted proteoglycans.

RESULTS

Versican mRNA was first expressed in the thickened dental epithelium at E12.0 and continued to be expressed in the enamel organ until the bell stage. Versican immunostaining was detected in the stellate reticulum areas from the bud stage to the apposition stage. The enamel organ at E16.0 expressed versican mRNA at a level comparable to that in dental mesenchyme. Furthermore, when compared to dental mesenchyme, about 1/2-3/4 of the [(35)S]-labelled versican-like large proteoglycan was synthesised and released into tissue explants by the enamel organ.

CONCLUSIONS

The dental epithelium of developing tooth germ is able to synthesise significant amounts of versican.

Two related but distinct chondroitin sulfate mimetope octasaccharide sequences recognized by monoclonal antibody WF6

Chondroitin sulfate (CS) proteoglycans are major components of cartilage and other connective tissues. The monoclonal antibody WF6, developed against embryonic shark cartilage CS, recognizes an epitope in CS chains, which is expressed in ovarian cancer and variably in joint diseases. To elucidate the structure of the epitope, we isolated oligosaccharide fractions from a partial chondroitinase ABC digest of shark cartilage CS-C and established their chain length, disaccharide composition, sulfate content, and sulfation pattern. These structurally defined oligosaccharide fractions were characterized for binding to WF6 by enzyme-linked immunosorbent assay using an oligosaccharide microarray prepared with CS oligosaccharides derivatized with a fluorescent aminolipid. The lowest molecular weight fraction recognized by WF6 contained octasaccharides, which were split into five subfractions. The most reactive subfraction contained several distinct octasaccharide sequences. Two octasaccharides, DeltaD-C-C-C and DeltaC-C-A-D (where A represents GlcUAbeta1-3GalNAc(4-O-sulfate), C is GlcUAbeta1-3Gal-NAc(6-O-sulfate), D is GlcUA(2-O-sulfate)beta1-3GalNAc(6-O-sulfate), DeltaCis Delta(4,5)HexUAalpha1-3GalNAc(6-O-sulfate), and DeltaDis Delta(4,5)HexUA(2-O-sulfate)alpha1-3GalNAc(6-O-sulfate)), were recognized by WF6, but other related octasaccharides, DeltaC-A-D-C and DeltaC-C-C-C, were not. The structure and sequences of both the binding and nonbinding octasaccharides were compared by computer modeling, which revealed a remarkable similarity between the shape and distribution of the electrostatic potential in the two different octasaccharide sequences that bound to WF6 and that differed from the nonbinding octasaccharides. The strong similarity in structure predicted for the two binding CS octasaccharides (DeltaD-C-C-C and DeltaC-C-A-D) provided a possible explanation for their similar affinity for WF6, although they differed in sequence and thus form two specific mimetopes for the antibody.

Porcine N-acetylgalactosamine 6-sulfatase (GALNS) cDNA sequence and expression in developing teeth

Mucopolysaccharidosis type IVA (Morquio A syndrome, MPS IVA) is a rare, autosomal recessive disorder with a prevalence of 1 in 170,000 live births. It is caused by a deficiency of N-acetylgalactosamine 6-sulfatase (GALNS), a lysosomal hydrolase encoded by a gene on human chromosome 16q24.3. Mucopolysaccharidosis type IVA is the only known MPS that is associated with structural defects in dental enamel. GALNS cleaves the sulfate group from N-acetylgalactosamine 6-sulfate and galactose 6-sulfate, which are specifically found in keratan sulfate and chondroitin 6-sulfate. A pathologic absence of GALNS activity results in the accumulation of these glycosaminoaglycans in the urine and in the lysosomes of tissues that turn them over. There is currently no animal model for MPS IVA. To learn more about how a GALNS deficit could lead to enamel defects, we have cloned and characterized a full-length pig GALNS cDNA. GALNS mRNA was localized in developing teeth by in situ hybridization, Northern blot, and reverse-transcription polymerase chain reaction analyses, while GALNS substrates were localized using immunohistochemistry. We report that secretory ameloblasts were positive for GALNS mRNA, as well as for keratan sulfate and chondroitin 6-sulfate. We conclude that enamel defects associated with the loss of GALNS activity in persons with MPS IVA are likely to result from the pathological accumulation of keratan sulfate and chondroitin 6-sulfate in the lysosomes of secretory stage ameloblasts.

The whereabouts of a morphogen: direct evidence for short- and graded long-range activity of hedgehog signaling peptides

Sonic Hedgehog (Shh) and Indian Hedgehog (Ihh) are members of the Hedgehog (Hh) family of signaling molecules known to be involved in embryonic patterning and morphogenesis. The Hh proteins undergo an autocatalytic cleavage to yield an N-terminal and a C-terminal peptide, with the signaling capacities confined to the N peptide. Drosophila Hh-N has been shown to act via both short- and long-range signaling. In vertebrates, however, attempts to directly demonstrate Shh (SHH) or Ihh (IHH) proteins at a distance from producing cells have been largely unsuccessful. Furthermore, the fact that the Hh N peptides occur in a cholesterol-modified, membrane-tethered form is not easily reconciled with long-range signaling. This study used optimized immunohistochemistry combined with tissue separation and biochemical analyses in vivo and in vitro to determine the range of action of SHH and IHH in the mouse embryo. In all embryonic structures studied, we detect signaling peptides in producing cells, but we also find that ligands move over considerable distances depending on the tissue. These data provide direct evidence for the presence of Hedgehog signaling peptides in target compartments, suggesting a direct long-range action without a need for secondary mediators. Visualization of Hedgehog proteins in target tissues was achieved only under conditions that allowed proteoglycan/glycosaminoglycan (PG/GAG) preservation. Furthermore, we show that induced changes of the composition of PG/GAG in the tooth alter SHH signaling. These data suggest a crucial role for PG/GAGs in Hedgehog movement.

Epigenetic signals during odontoblast differentiation

Odontoblast terminal differentiation occurs according to a tooth-specific pattern and implies both temporospatially regulated epigenetic signaling and the expression of specific competence. Differentiation of odontoblasts (withdrawal from the cell cycle, cytological polarization, and secretion of predentin/dentin) is controlled by the inner dental epithelium, and the basement membrane (BM) plays a major role both as a substrate and as a reservoir of paracrine molecules. Cytological differentiation implies changes in the organization of the cytoskeleton and is controlled by cytoskeleton-plasma membrane-extracellular matrix interactions. Fibronectin is re-distributed during odontoblast polarization and interacts with cell-surface molecules. A non-integrin 165-kDa fibronectin-binding protein, transiently expressed by odontoblasts, is involved in microfilament reorganization. Growth factors (TGF beta 1, 2, 3/BMP2, 4, and 6), expressed in tooth germs, signal differentiation. Systemically derived molecules (IGF1) may also intervene. IGF1 stimulates cytological but not functional differentiation of odontoblasts: The two events can thus be separated. Immobilized TGF beta 1 (combined with heparin) induced odontoblast differentiation. Only immobilized TGF beta 1 and 3 or a combination of FGF1 and TGF beta 1 stimulated the differentiation of functional odontoblasts over extended areas and allowed for maintenance of gradients of differentiation. Presentation of active molecules in vitro appeared to be of major importance; the BM should fulfill this role in vivo by immobilizing and spatially presenting TGF beta s. Attempts are being made to investigate the mechanisms which spatially control the initiation of odontoblast differentiation and those which regulate its propagation. Analysis of molar development suggested that odontoblast differentiation and crown morphogenesis are interdependent, although the possibility of co-regulation requires further investigation.

Pneumococcal virulence factors: structure and function

The overall goal for this review is to summarize the current body of knowledge about the structure and function of major known antigens of Streptococcus pneumoniae, a major gram-positive bacterial pathogen of humans. This information is then related to the role of these proteins in pneumococcal pathogenesis and in the development of new vaccines and/or other antimicrobial agents. S. pneumoniae is the most common cause of fatal community-acquired pneumonia in the elderly and is also one of the most common causes of middle ear infections and meningitis in children. The present vaccine for the pneumococcus consists of a mixture of 23 different capsular polysaccharides. While this vaccine is very effective in young adults, who are normally at low risk of serious disease, it is only about 60% effective in the elderly. In children younger than 2 years the vaccine is ineffective and is not recommended due to the inability of this age group to mount an antibody response to the pneumococcal polysaccharides. Antimicrobial drugs such as penicillin have diminished the risk from pneumococcal disease. Several pneumococcal proteins including pneumococcal surface proteins A and C, hyaluronate lyase, pneumolysin, autolysin, pneumococcal surface antigen A, choline binding protein A, and two neuraminidase enzymes are being investigated as potential vaccine or drug targets. Essentially all of these antigens have been or are being investigated on a structural level in addition to being characterized biochemically. Recently, three-dimensional structures for hyaluronate lyase and pneumococcal surface antigen A became available from X-ray crystallography determinations. Also, modeling studies based on biophysical measurements provided more information about the structures of pneumolysin and pneumococcal surface protein A. Structural and biochemical studies of these pneumococcal virulence factors have facilitated the development of novel antibiotics or protein antigen-based vaccines as an alternative to polysaccharide-based vaccines for the treatment of pneumococcal disease.

Expression of laminin-5 in ameloblastomas and human fetal teeth

Extracellular matrix proteins have been shown to play important roles in the cell migration and differentiation in both normal and pathological conditions. In the present study, we used immunohistochemistry and in situ hybridization to determine the distribution of laminin-5 in ameloblastomas and developing human teeth. In ameloblastomas, the immunoreaction for the laminin-5 gamma2 chain was confined to the tumor cells of the peripheral area. The staining reaction was variable, being mostly weak and fragmented in the basement membrane structures surrounding the neoplastic islands. Some peripheral epithelial cells and some invading small ameloblastoma cell islands showed intense intracellular staining for the gamma2 chain. Tumor cells in the proliferating areas of ameloblastomas expressed gamma2 chain mRNA. The laminin-5 gamma2 chain was located beneath the dental lamina and in the outer, but not in the inner, enamel epithelium of the developing teeth. During the early hard tissue apposition stage, intense staining for the gamma2 chain was confined to ameloblasts, which also gave a strong signal for gamma2 chain mRNA. These results suggest that laminin-5 may contribute to the infiltrative and progressive growing potential of ameloblastomas. During human tooth development, however, laminin-5 may participate in the terminal differentiation of ameloblasts and in enamel matrix formation.

Sequential distribution of keratan sulphate and chondroitin sulphate epitopes during ameloblast differentiation

Proteoglycans are complex macromolecules containing one or more glycosaminoglycan chains and exhibiting a variety of biological functions in connective tissues. The aim of the present study was to immunolocalize the distribution of keratan sulphate and chondroitin sulphate epitopes during initial enamel formation in order to study temporo-spatial expression patterns of these macromolecules. Third molars of four-months-old pigs were used for immunolocalization of keratan sulphate and chondroitin sulphate epitopes in the developing enamel layer. Tooth organs were prepared for paraffin sections in order to perform indirect immunohistochemistry. The results demonstrated a mutually exclusive positioning between these two epitopes. Keratan sulphate epitopes were observed in pre-secretory pre-ameloblasts and adjacent stratum intermedium while chondroitin sulphate epitopes were demonstrated in secretory ameloblasts and adjacent stratum intermedium. Our findings suggest that proteoglycans containing glycosaminoglycan chains may play a regulatory role during enamel mineralization.

Chondroitin sulphate and heparan sulfate proteoglycan are sequentially expressed in the uterine extracellular matrix during early pregnancy in the rat

Chondroitin sulfate proteoglycan (CSPG) and heparan sulfate proteoglycan (HSPG) are extracellular matrix proteins that regulate cell adhesion, growth, migration, differentiation and gene expression in many systems. In this study, stromal CSPG label was intense within 10 microm of the uterine lumen. From that distance to the myometrium, CSPG was de-expressed. From the time of implantation on Day 6, this pattern was reversed. CSPG was de-expressed from the uterine epithelium to a distance of approximately 10 microm from the uterine lumen. From that region to the myometrium, labeling was homogeneously intense. This finding suggests that CSPG may inhibit attachment and implantation. Heparan sulfate core proteoglycan (perlecan) was increasingly expressed in the uterine epithelium from the time of implantation, commencing in the basement membrane on Day 6 and extending to the apical epithelium and lateral plasma membranes by Day 7. Perlecan thus appears to facilitate trophoblast attachment and implantation. We propose that attachment and implantation is regulated, at least in part, by the selective and sequential expression of CSPG and perlecan.

Quantitative immunohistochemical evidence of a functional gradient of chondroitin 4-sulphate/dermatan sulphate, developmentally regulated in the predentine of rat incisor

A quantitative examination was carried out on the early and mature stages of dentinogenesis in the rat incisor, using a post-embedding immunogold labelling with an anti-chondroitin 4 sulphate/dermatan sulphate antibody (2B6). At a very early stage of predentine formation, before polarizing odontoblasts have established junctional complexes, immunolabelling was weak. In contrast, when polarized odontoblasts established distal junctional complexes, immunolabelling in predentine was uniform and threefold denser than in initial predentine. The same gold particle density was found in the non-mineralized mantle dentine. During circumpulpal dentine formation, a gradient was seen in predentine, a larger number of gold particles being scored in the proximal zone compared with the distal region adjacent to the mineralization front. In circumpulpal dentine, some labelling was found within the lumen of the tubules and in the bordering dentine around the tubules. A few particles were also detected in intertubular matrix after demineralization. Together, these data provide evidence for a developmentally regulated gradient during the transition between mantle and circumpulpal dentine, and also in a more mature part of the tooth, a functional gradient that probably plays a role in the process of mineralization.

Expression and localization of laminin-5 subunits during mouse tooth development

Tooth morphogenesis is regulated by epithelial-mesenchymal interactions mediated by the basement membrane (BM). Laminins are major glycoprotein components of the BMs, which are involved in several cellular activities. The expression and localization of the alpha3, beta3, and gamma2 laminin-5 subunits have been analyzed by in situ hybridization and immunohistochemistry during mouse molar development. Initially (E12), mRNAs of all subunits were detected in the entire dental epithelium and the corresponding proteins were located in the BM. During cap formation (E13-14), transcripts for the alpha3 and gamma2 subunits were localized in the outer dental epithelium (ODE), whereas the beta3 subunit mRNA was present in the inner dental epithelium (IDE). During the early bell stage (E16), immunoreactivity for all subunits disappeared from the BM along the IDE, although intense signals for beta3 mRNA were detectable in cells of the IDE. Subsequently, when the dentinal matrix was secreted by odontoblasts (E18-19.5), mRNAs of all three subunits were re-expressed by ameloblasts, and the corresponding proteins were detected in ameloblasts and in the enamel matrix. Tissue recombination experiments demonstrated that when E16 IDE or ODE was associated with E18 dental papilla mesenchyme, immunostaining for all laminin-5 subunits disappeared from the BM, whereas when cultured with non-dental limb bud mesenchyme, they remained positive after 48 hr of culture. These results suggest that the temporospatial expression of laminin-5 subunits in tooth development, which appears to be differentially controlled by the dental mesenchyme, might be related to the enamel organ histo-morphogenesis and the ameloblast differentiation.

Light and electron microscopical immunohistochemical localization of large proteoglycans in human tooth germs at the bell stage

The immunohistochemical localization of large hyaluronate-binding proteoglycans has been studied in human tooth germs at the bell stage using a monoclonal antibody, 5D5, which is derived from bovine sclera and specifically recognizes the core protein of large proteoglycans, such as versican, neurocan and brevican, but not that of aggrecan. In the early bell stage before predentine secretion, when the enamel organs consisted of the inner and outer enamel epithelia, stratum intermedium and stellate reticulum, the enamel organs were not stained by 5D5, but the dental papillae and follicles stained strongly. Concomitant with the secretion of predentine, dentine and subsequent enamel matrix, strong 5D5 immunostaining distributed over the entire cell surfaces of secretory ameloblasts was observed. The forming enamel matrix showed strong staining. While most of the inner and outer enamel epithelia and stratum intermedium lacked staining, the cervical loop region and stellate reticulum showed weak staining. Although the forming dentine and odontoblasts appeared to lack 5D5 affinity, the predentine, dental papilla and dental follicle demonstrated moderate to strong reactivity. At the ultrastructural level, specific immunoreaction by immunogold particle deposition was clearly detected over the basal lamina of presecretory ameloblasts, secretion granules of secretory ameloblasts and the forming enamel matrix. These results indicate that a marked increase in the large proteoglycan associated with secretory ameloblasts may correlate with cell differentiation and enamel matrix biosynthesis.

Preparation of a series of sulfated tetrasaccharides from shark cartilage chondroitin sulfate D using testicular hyaluronidase and structure determination by 500 MHz 1H NMR spectroscopy

Six tetrasaccharide fractions were isolated from shark cartilage chondroitin sulfate D by gel filtration chromatography followed by HPLC on an amine-bound silica column after exhaustive digestion with testicular hyaluronidase. Their structures were determined unambiguously by one- and two-dimensional 500 MHz 1H NMR spectroscopy in conjunction with HPLC analysis of chondroitinase AC-II digests of the tetrasaccharides. One fraction was found to contain two tetrasaccharide components. All of the seven tetrasaccharides shared the common core structure GlcA beta 1-3GalNAc beta 1-4GLcA beta 1-3GalNAc with various sulfation profiles. Four were disulfated comprising of two monosulfated disaccharide units GLcA beta 1-3GalNAc(4-sulfate) and/or GlcA beta 1-3GalNAc(6-sulfate), whereas the other three were hitherto unreported trisulfated tetrasaccharides containing a disulfated disaccharide unit GlcA(2-sulfate)beta 1-3GalNAc(6-sulfate) and a monosulfated disaccharide unit GlcA beta 1-3GalNac(4- or 6-sulfate). These sulfated tetrasaccharides were demonstrated to serve as appropriate acceptor substrates for serum alpha-N-acetylgalactosaminyltransferase, indicating their usefulness as authentic oligosaccharide substrates or probes for the glycobiology of sulfated glycosaminoglycans.

Effect of growth hormone on the distribution of decorin and biglycan during odontogenesis in the rat incisor

Previous studies have shown that growth hormone can influence the expression of N-acetylgalactosamine-containing molecules in the extracellular matrix of developing rat incisors. N-acetylgalactosamine is a principal component of proteoglycans containing chondroitin sulfate and dermatan sulfate, as well as of some glycoproteins. Since chondroitin sulfate proteoglycans are identifiable components in enamel, dentin, and cementum, we have tested the hypothesis that growth hormone modulates their expression in developing rat incisors. The distribution of the chondroitin-sulfate-rich proteoglycans, decorin and biglycan, was investigated. We used the Lewis dwarf rat as a model because their circulating growth hormone levels are markedly reduced. Polyclonal antibodies against decorin and biglycan were used to localize these two proteoglycans. Semi-quantitative assessments of the staining patterns and intensities were made for each proteoglycan within compartments of the developing teeth. In normal Lewis rats, decorin and biglycan differentially expressed throughout the enamel organ, dental papilla, and dental follicle. Decorin displayed a wide distribution throughout all three regions and was closely associated with different cellular components. In contrast, biglycan showed little association with cells and was identified in the predentin and osteoid matrices. The expression of both proteoglycans was dramatically decreased in the growth-hormone-deficient animals. Administration of growth hormone to the dwarf rats markedly elevated the expression of both proteoglycans, approximating the distribution and intensity of staining seen in normal animals. These findings confirm that growth hormone status can modulate the expression of decorin and biglycan, and hence matrix deposition, in the rat tooth.

Cultured incisors display major modifications in basal lamina deposition without further effect on odontoblast differentiation

Matrix-mediated epithelio-mesenchymal interactions play a crucial role in the control of dental cytodifferentiations. Ultrastructural observation of the epithelio-mesenchymal junction in cultured embryonic mouse molars showed discrete zones with duplicated or multilayered basal laminae. The use of synthetic peptides demonstrated that the process was RGD*-independent, did not involve the YIGSR* sequence present on laminin and could occur spontaneously. Cultured incisors showed a similar but much more dramatic multiplication of the basal laminae. Furthermore, the deposition of multilayered basal laminae was specific for the labial aspect of the tooth and could be detected after 6 h of culture. Despite these alterations, preodontoblasts differentiated and gradients of differentiation were maintained, suggesting that among basement membrane constituents, the basal lamina itself does not play a critical role. More important is the inner dental epithelium which may still control odontoblast differentiation by means of diffusible molecules able to reach surface receptors expressed by preodontoblasts or matrix receptors underlying the basal lamina. Gradients of odontoblast differentiation could result from a progressive acquisition of competence by preodontoblasts.

Development of sensory innervation in chick skin: comparison of nerve fibre and chondroitin sulphate distributions in vivo and in vitro

In bird skin, nerve fibres develop in the dermis but do not enter the epidermis. In co-cultures of 7-day-old chick embryo dorsal root ganglia and epidermis, the neurites also avoid the epidermis. Previous studies have shown that chondroitin sulphate proteoglycans may be involved. Chondroitin sulphate has therefore been visualized by immunocytochemistry, using the monoclonal antibody CS-56, both in vivo and in vitro using light and electron microscopy. Its distribution was compared to those of 2 other chondroitin sulphate epitopes and to that of the growing nerve fibres. In cultures of epidermis from 7-day-old embryonic chicks, immunoreactivity is found uniformly around the epidermal cells while at 7.5 days the distribution in dermis is heterogeneous, and particularly marked in feather buds. In vivo, chondroitin sulphate immunoreactivity is detected in the epidermis, on the basal lamina, on the surfaces of fibroblasts and along collagen fibrils. This localization is complementary to the distribution of cutaneous nerves. Chondroitin sulphate in the basal lamina could prevent innervation of the epidermis and the dermal heterogeneities could partly explain the nerve fibres surrounding the base of the feathers. Chondroitin sulphate could therefore be important for neural guidance in developing chick skin.

Growth hormone regulates an N-acetylgalactosamine component in odontogenesis: a specific lectin-binding study in the Lewis dwarf rat

Dental organs of incisors from normal, dwarf and growth hormone-treated dwarf rats were analysed histochemically using a panel of lectins. A distinctive pattern of differential staining was obtained with Helix pomatia agglutinin, a lectin specific for N-acetylgalactosamine. In Bouin's perfused and paraffin-embedded undecalcified tissues from normal rats, reaction product for N-acetylgalactosamine was visible in the odontogenic cells and some extracellular matrices. In the growth hormone-deficient dwarf rats, the N-acetylgalactosamine reaction was consistently minimal in the odontoblasts, predentin, cementoblasts, cementoid, osteoblasts and osteoid matrices, although the staining of ameloblasts and osteoclasts was similar to normal. Administration of growth hormone to dwarf rats for six days (66 micrograms/100 g rat b.i.d.) restored the reaction for N-acetylgalactosamine in the affected matrices. Thus, an N-acetylgalactosamine rich matric component is differentially expressed during odontogensis. Growth hormone may regulate this component in these matrices, which may be a proteoglycan or a glycoprotein, essential for normal growth of the teeth.

A chondroitin sulfate epitope in mammalian dental pulp and its developmental expression in mouse dental papilla

The molecular specificity of the dental papilla of a bell-stage tooth was studied by production of dental-papilla-reactive monoclonal antibodies (Mabs). One of the Mabs, designated 7C5, recognized an epitope present in glycosaminoglycan. Several lines of evidence suggested that the 7C5-epitope consists of chondroitin 6-sulfate. The Mab did not react with mouse dental epithelium, but reacted uniformly with mesenchymal tissue in the mandibular process and accumulated in the dental sac and in the papilla of bell-stage tooth germs. The 7C5-staining was lost from the differentiating odontoblasts, while the staining in the molar tooth papilla was accumulated in the subodontoblastic layer. In the developing mouse incisor, the 7C5-epitope was restricted to the lingual-posterior area. The 7C5-epitope was also present in pulpal tissue and predentin of different types of teeth of various mammalian species, including man, sheep, swine, and rat. Collagenase pre-treatment of tissue sections abolished the bulk of the 7C5-reactivity in peridental mesenchyme during embryonic stages while leaving the staining of the dental papilla intact. In newborn and adult teeth, collagenase also impaired the reactivity in the pulp except for the subodontoblastic layer. This suggests the existence of different subpopulations of the 7C5-epitope containing proteoglycans in dental papilla and pulp. A high-molecular-weight proteoglycan, sensitive to chondroitinase ABC but not to heparinase or heparitinase, was immunoprecipitated by 7C5 from extracts of bell-stage mouse tooth germs. We suggest that the evolutionary conservation of chondroitin 6-sulfate in the dental pulp reflects its properties as non-terminally differentiated tissue and perhaps the retention of a potential to differentiate to odontoblasts.

Dentin sialoprotein: biosynthesis and developmental appearance in rat tooth germs in comparison with amelogenins, osteocalcin and collagen type-I

A non-collagenous protein, extracted from rat incisor dentin, is a dentin sialoprotein (DSP). We examined immunohistochemically the developmental appearance and tissue distribution of DSP in 1 to 3-day-old rat molar and incisor tooth germs. The earliest staining for DSP was observed in newly differentiated odontoblasts. In more advanced stages, immunostaining for DSP gradually increased in pre-dentin, odontoblasts and dentin, and appeared in many cells of the dental papilla. In early stages of development before the breakdown of the dental basement membrane, pre-ameloblasts were also positive for DSP. This staining disappeared from the ameloblast cell body soon after deposition of the first layer of mineralized dentin. Radiolabelling of tooth matrix proteins with 14C-serine in vitro followed by immunoprecipitation and fluorography confirmed that DSP was synthesized by tooth-forming cells. The immunolocalization for DSP was different from that of either collagen type-I, osteocalcin or the amelogenins. Whereas collagen type-I and osteocalcin were restricted to the mesenchymal dental tissues, the amelogenins were detectable in both epithelial and mesenchymal dental cells and tissues at the epithelio-mesenchymal interface at early stages of development, prior to the onset of dentin mineralization. We conclude that DSP is expressed in and secreted by odontoblasts and some dental papilla cells from early stages of dentinogenesis onwards, i.e. later than type-I collagen, but before deposition of the first layer of mineralized dentin. In pre-mineralizing stages, some of the matrix proteins may be endocytosed from the pre-dentin by both cell types involved in the epithelio-mesenchymal interaction.

Retardation of mouse odontoblast differentiation by heparin in vitro

The effect of heparin was studied histologically and immunohistochemically. Tooth germs from 15-day-old mouse embryos were cultured with or without heparin. After 6 days of culture in control medium, mesenchymal cells underlying the inner enamel epithelium had differentiated into odontoblasts and secreted predentine. In medium with heparin, mesenchymal cells were undifferentiated. In medium with other glycosaminoglycans such as chondroitin sulphate, dermatan sulphate or hyaluronate, tooth germs were similar to those in control medium, as were those in medium with heparin-Sepharose absorbed serum. After 12 days of culture in the heparin medium, mesenchymal cells in some cusps had differentiated into odontoblasts and secreted predentine but in other cusps remained undifferentiated. Immunohistochemically, exogenous heparin did not prevent the deposition of type IV collagen, laminin and fibronectin in the basement membrane and extracellular matrix. These results suggest that exogenous heparin retards differentiation of odontoblasts but not by disruption of the basement membrane nor inactivation of heparin-binding growth factors present in serum.

Fate of ciliated epidermal cells during early development of Xenopus laevis using whole-mount immunostaining with an antibody against chondroitin 6-sulfate proteoglycan and anti-tubulin: transdifferentiation or metaplasia of amphibian epidermis

Xenopus embryonic epidermis changes its cellular composition during development: the appearance of ciliated epidermal cells before hatching is a remarkable characteristic. In this study, the functional change of ciliated cells to mucus-secreting cells was examined with immunocytochemistry using anti-tubulin and anti-chondroitin 6-sulfate (C6S). Before hatching, most epidermal cells were labeled with anti-C6S in a granular fashion. Immunoelectron microscopy revealed that the anti-C6S-positive structure was the mucus granule. Ciliated epidermal cells lacked anti-C6S staining, but were strongly labeled with anti-tubulin. After hatching, most ciliated cells in the surface of the embryo disappeared. During their disappearance, some ciliated cells exhibited anti-C6S-positive granular labeling. This strongly suggests that the disappearance of ciliated cells is a functional conversion to mucus-secreting cells instead of shedding through cell death.

Growth hormone regulates nucleolar organizer regions during odontogenesis in the rat

Nucleolar organizers are major sites of ribosomal RNA synthesis and provide an index of transcriptional activity. In order to further define growth hormone actions on nucleolar organizer regions in tooth forming cells, hypophysectomized rats treated with growth hormone for 4 and 24 h, hypophysectomized and sham-operated animals were used. After demineralization and standard paraffin embedding, longitudinal sections of maxillary incisors were stained by a silver stain technique to reveal nucleolar organizer regions. The area of these regions per nucleus was measured using a modified microdensitometer. Analyses of variance of the resulting data showed that preameloblasts and preodontoblasts have greater silver stained nucleolar organizer region values than ameloblasts and odontoblasts. Hypophysectomy reduced and growth hormone partly restored the level of nucleolar organizer regions in preameloblasts and preodontoblasts, but not in mature ameloblasts or odontoblasts. In the case of the younger preameloblasts and preodontoblasts, the effect of growth hormone was seen within 4 h of growth hormone injection. In conclusion, rRNA synthesis, as revealed by the specific silver staining of nucleolar organizer regions in tooth forming cells, appears to be regulated by growth hormone over a relatively short time frame.

Differential staining of glycosaminoglycans in the predentine and dentine of rat incisor using cuprolinic blue at various magnesium chloride concentrations

Rat incisors were fixed with a solution of 0.05% Cuprolinic Blue and 2.5% glutaraldehyde in the presence of various concentrations of MgCl2 according to the critical electrolyte concentration (CEC) principle. This method allows glycosaminoglycans (GAG) to be properly preserved and visualized. Small granules were stained by the cationic dye in the predentine in the absence of MgCl2. These granules grew in size and became more electron-dense when the concentration of the electrolyte was increased. Larger ribbon-like structures and granules were seen when 0.3 M MgCl2 was used. In the dentine, tiny dots in close association with the surface of the collagen fibres, or their periodic striations, were positively stained. A thick electron-dense band located on the dentine side at the predentine-dentine junction was seen both with and without 0.05 M MgCl2. With higher concentrations of the electrolyte (0.1-0.3 M), this band was reduced to a very thin line located at the border of the dentine, along with mineralizing collagen fibres. This demonstrated the presence of GAG at the dentine surface and therefore indicated that GAG may play a role as nucleator agent.

The correlation of temporal regulation of glycosaminoglycan synthesis with morphogenetic events in mouse tooth development

The purpose of this study was to investigate the pattern of sulphated glycosaminoglycan synthesis during morphogenesis and cytodifferentiation in mouse tooth rudiments and to compare the results with those obtained in another study for salivary gland, a branched organ. Sulphated glycosaminoglycan was labelled by incubating molar rudiments from day 15 of gestation to day 1 post partum in medium containing [35S]-sodium sulphate. The rudiments were washed, homogenized and digested in pronase and then were sequentially digested by chondroitinase ABC and chemically degraded by nitrous acid oxidation. The fractions from each of these procedures were analysed by chromatography on Sephadex G-50 columns. The analysis revealed that, during morphogenesis, levels of chondroitin sulphate increased to a peak of 91% at day 18 and levels of heparan sulphate diminished to 8% during this period. As cytodifferentiation occurred, the level of chondroitin sulphate dropped to 64% and that of heparan sulphate increased to 35%. These results are similar to those reported for rat submaxillary gland, a branching organ. It appears that this pattern of sulphated glycosaminoglycan synthesis is not a unique feature of branching morphogenesis but may be one which marks the transition between morphogenesis and cytodifferentiation in non-branching rudiments as well.

Involvement of cellular retinoic acid-binding proteins I and II (CRABPI and CRABPII) and of the cellular retinol-binding protein I (CRBPI) in odontogenesis in the mouse

The coordination of the activities of individual cells during development is regulated in part by epigenetic signals either encoded in the insoluble extracellular matrix or provided by small diffusible factors such as growth factors peptides and retinoids. Odontogenesis offers a suitable model to correlate the temporospatial distributions of such molecules, and of their cell receptors and ligands, with particular developmental processes. We have analyzed, by in situ hybridization, the distribution patterns of CRABPI, CRABPII and CRBPI transcripts during odontogenesis in the mouse. CRABPI transcripts were restricted to the mitogenic regions of the dental mesenchyme during late bell stages and were absent from post-mitotic odontoblasts. The only epithelial site of CRABPI transcription was the labial epithelial loop of the continuously growing incisor. CRABPII transcription was preponderant in the mitogenic zones of the dental epithelium: differential labeling of the dental epithelium occurred as early as the dental bud stage and during subsequent molar morphogenesis, this labeling became confined in the epithelial loops. The graded distribution of CRABPII transcripts along the anteroposterior axis of the continuously growing incisor was superimposed with the gradient of mitoses. CRABPII transcripts were absent from post-mitotic ameloblasts. It is concluded that during odontogenesis the expressions of the CRABPI and CRABPII genes are confined to regions exhibiting the highest rate of cell proliferation whenever differential mitotic activity is required. Moreover, the putative effects of retinoic acid on the regulation of cell proliferation kinetics in the dental epithelium and in the dental mesenchyme imply distinct CRABPs. CRBPI transcripts were restricted to the dental mesenchyme prior to the onset of CRABPI transcription. This observation supports the hypothesis that the two proteins might perform antagonistic functions in some retinoic acid-mediated developmental processes.

Ultrastructural and immunocytochemical study of bone-derived cells cultured in three-dimensional matrices: influence of chondroitin-4 sulfate on mineralization

Bone-derived cells were cultured in three-dimensional reconstituted matrices made of type I collagen or type I collagen chondroitin-4-sulfate. As observed by microscope, their characteristics were as follows: The cells deposited a faint extracellular matrix mainly composed of type I collagen. In the collagen-chondroitin-sulfate sponge fibers, a calcification process, which involved the deposition of hydroxyapatite crystals, was demonstrated. Mineralization occurred only in collagen chondroitin sulfate sponge fibers when seeded with bone-derived cells and was not seen with nonosteogenic cells, such as gingival fibroblasts. Gla protein was intracellularly visualized in both types of sponges seeded with bone-derived cells while an extracellular secretion was seen only in the collagen chondroitin sulfate sponge fibers where calcification occurred. These results suggest that collagen chondroitin sulfate promotes in vitro mineralization of three-dimensional collagen matrices when seeded with bone-derived cells.

Effects of beta-D-xyloside on morphogenesis and cytodifferentiation in cultured embryonic mouse molars

Embryonic mouse molars were grown on a semi-solid medium supplemented with 2 mM beta-D-xylopyranoside (beta-xyloside), a specific inhibitor of proteoglycan synthesis. The induced glycosaminoglycan depletion in the extracellular matrix was monitored by immunohistochemistry employing monoclonal antibodies to chondroitin 4- and chondroitin 6-sulfates. beta-Xyloside inhibited formation of the dental bell and delayed the appearance of the first odontoblasts. Odontoblast functional differentiation proceeded in the absence of chondroitin sulfate in the basement membrane. Predentin secreted in the presence of beta-xyloside triggered the polarization of ameloblasts, but did not allow the maintenance of polarized odontoblasts. These results support the hypothesis that, in the tooth germ, chondroitin sulfate proteoglycans participate in the regulation of cell kinetic-dependent morphogenesis (Mark et al., 1990. Differentiation 43, 37-50). On the other hand, the possibility that chondroitin sulfate might play a role in odontoblast terminal differentiation is definitively ruled out.