The distribution of cellular retinoic acid-binding protein I during odontogenesis in the rat incisor

Oral biology and disorders of lagomorphs

Rabbit medicine, and dentistry in particular, is still at an early stage of development. With an understanding of the underlying oral physiology it is possible to devise an appropriate treatment regime for most dental problems after the nature and extent of disease has been assessed. Although many of the dental problems that are seen in practice cannot be cured, most can be controlled or managed to allow the affected rabbit to maintain a good quality of life. The continuously growing nature of the teeth makes recurrence and progression of problems the norm, so owner education and ongoing monitoring of animals is essential. By assessing the effects, beneficial or otherwise, of out treatments and communicating this to others, we will develop our knowledge and skills. Several treatments that are suggested in this article must be considered as "experimental" because they have not been assessed in large numbers of animals. If they work for you, or more importantly, if you find unexpected complications with a treatment method (as has happened with the use of calcium hydroxide paste treatment of abscess cavities) then please publicize the fact so that others can avoid the problem. Until the message on prevention can be reliably transmitted to owners, we will continue to have oral and dental problems to manage. After confidence and experience has been gained in anesthetizing rabbits it is possible to refine one's dental skills to be able to rapidly perform a thorough examination and basic treatments. Major and complex treatments require careful consideration because they may add to the animal's problems, rather than improving the situation. The best method for learning rabbit dentistry is to routinely perform postmortem examinations following euthanasia of affected animals, and spend an hour or two practicing handling the instruments and performing procedures on a cadaver. If you are not confident in your ability or do not have the best equipment for the job, the client should be informed and offered the opportunity to be referral to a "specialist."

The distribution of retinaldehyde dehydrogenase-2 in rat and human orodental tissues

Retinoic acid is an important signalling molecule in embryological development and continues to be important in the adult animal because it modulates growth and differentiation in many epithelial tissues. The distribution of the enzyme retinaldehyde dehydrogenase-2 (RALDH 2), which is involved in the synthesis of retinoic acid, was studied using immunocytochemical techniques in: (1) the developing orodental region of rats aged between 15 days in utero and 6 months; and (2) in archival human autopsy material consisting of abdominal skin and mucosa from various regions of the mouth. In developing tooth germs, RALDH 2 was absent in the enamel organ and dental papilla, its presence only being noted at the periphery of the dental follicle adjacent to parts of the developing alveolar crypt. In adult teeth, the presence of RALDH 2 was limited to blood vessels in the periodontal ligament. In embryos, the connective tissue beneath the nasal epithelium and the meninges stained strongly positively for RALDH 2, as did the connective tissue beneath nasal epithelium in an adult rat. Both keratinized and non-keratinized human oral epithelia and abdominal skin stained positively for RALDH 2. Staining was present throughout the stratified epithelium, except in the keratinized layer and in the basal layer associated with the dorsal surface of the tongue. In addition, the adnexia as well as the ductal lining of mucous glands stained positively for RALDH 2.

Tissue-non-specific alkaline phosphatase mRNA expression and alkaline phosphatase activity following application of retinoic acid in cultured human dental pulp cells

Retinoic acid is a potent inducer of tissue-non-specific alkaline phosphatase (TNSALP) expression in various osteoblastic and fibroblastic cells, and may be involved in morphogenesis, cellular growth and differentiation. This study investigates the effects of retinoic acid on alkaline phosphatase activity and TNSALP gene expression in human dental pulp cells. Cultured cells were treated with various concentrations of retinoic acid (0, 10(-7), 10(- 6), 10 (-5) M) in 0.5% bovine serum albumin without serum. Alkaline phosphatase activity was determined by the rate of p-nitrophenyl phosphate hydrolysis and was also assayed in the presence of various inhibitors and under thermal inactivation. A set of specific oligonucleotide primers was selected, based on the nucleotide sequences of two human TNSALP mRNA (bone and liver) types, and reverse transcription-polymerase chain reaction (RT-PCR) performed. Inhibitory and thermal inactivation experiments revealed that the elevated alkaline phosphatase activity had properties of the TNSALP type. RT-PCR showed that retinoic acid enhanced the expression of bone-type TNSALP mRNA in pulp cells. However, the liver-type TNSALP mRNA was not detected. These findings suggest that the high alkaline phosphatase activity of retinoic acid-treated dental pulp cells is associated with increased transcription of the bone-type mRNA of the TNSALP gene and not with liver-type.

Effect of retinoic acid on osteopontin expression in rat clonal dental pulp cells

We studied the effect of retinoic acid on osteopontin synthesis and the mRNA expression in rat clonal dental pulp cells, RPC-C2A. An immunoprecipitation assay clarified that retinoic acid caused an increase in phosphorylated osteopontin synthesis that was dose-dependent, and marked increases were observed at retinoic acid concentrations of 10(-6) to 10(-5) M (1.7-fold). A Northern blotting analysis revealed a similar pattern of increase in osteopontin mRNA expression of up to 6.2-fold of control levels. Because osteopontin has an important role in the mineralization process, these results suggest that retinoic acid regulates mineralization, which takes place in the pulp cavity, including reparative dentin formation.

Antisense oligonucleotides to CRABP I and II alter the expression of TGF-beta 3, RAR-beta, and tenascin in primary cultures of embryonic palate cells

The cellular retinoic acid-binding proteins (CRABPs) are thought to modulate the responsiveness of cells to retinoic acid (RA). We have previously shown that primary cultures of murine embryonic palate mesenchymal (MEPM) cells express both CRABP-I and CRABP-II genes and that this expression is regulated by RA and transforming growth factor beta (TGF-beta). These cells also express high levels of TGF-beta 3, which is also regulated by RA and TGF-beta. We have used an antisense strategy to investigate the role of the CRABPs in retinoid-induced gene expression. Subconfluent cultures of MEPM cells were treated for several days with phosphorothioate modified 18-mer oligonucleotides antisense to CRABP-I or CRABP-II and then with all-trans-retinoic acid at a concentration of 3.3 microM or 0.33 microM for 5 or 22 h. Total RNA was then extracted and the expression of TGF-beta 3, retinoic acid receptor beta (RAR-beta), and tenascin was assessed by northern blot analysis. Antisense oligonucleotides to CRABP-I partially inhibited the RA-induced TGF-beta 3, RAR-beta, and tenascin mRNA expression. The corresponding mis-sense oligonucleotides were without effect. Antisense oligonucleotides to CRABP-II also partially inhibited RA-induced expression of these genes. As with the CRABP-I antisense, mis-sense oligonucleotides to CRABP-II had no effect. These data suggest that both CRABPs modulate the responsiveness of MEPM cells to retinoic acid. Inhibition of endogenous CRABP expression renders MEPM cells less responsive to RA with respect to induction of TGF-beta 3, RAR-beta, and tenascin gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of connexin 43 in the developing tooth germ of rat

Distribution of gap junction protein in maxillary tooth germs of 1-day-old rats was examined by immunohistochemistry, using an affinity-purified antibody specific to residues 360-376 of rat connexin (CX) 43. In 1-day-old rats, the maxillary second molar formed the shape of the cusp, but neither dentine nor enamel was formed between the cells of the dental papilla and the inner enamel epithelium. In the tooth germ, CX 43 was expressed in the cells of the stratum intermedium and the inner enamel epithelium. Labelling in the stratum intermedium was extensive and showed an increasing gradient from peripheral to cuspal regions. CX 43 detected in the inner enamel epithelium was at cell surfaces facing the interface between the dental papilla and the inner enamel epithelium. The cells of the dental papilla and the inner enamel epithelium began differentiation as odontoblasts and secretory ameloblasts respectively, in the cusps of the first molars, where predentine and dentine were formed but enamel matrix was not secreted. CX 43 was present in the stratum intermedium, inner enamel epithelium, preodontoblasts, odontoblasts and subodontoblasts. The incisors showed the most advanced stage of development, where the enamel matrix and calcified dentine were formed in the labial part of the teeth. The CX 43 epitope was seen in the stratum intermedium, inner enamel epithelium, preameloblasts, preodontoblasts, odontoblasts, and subodontoblasts. Immunolabelling was more extensive in the stratum intermedium and subodontoblasts than in preameloblasts, preodontoblasts, and odontoblasts. The immunolabelling in preameloblasts and predontoblasts was accumulated at cell surfaces facing the predentine.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of cellular retinoic acid-binding protein I (CRABPI) and cellular retinol-binding protein I (CRBPI) during molar tooth development and eruption in the rat

The distribution of cellular retinoic acid-binding protein (CRABPI) and cellular retinol binding protein (CRBPI) was studied in a series of prenatal and early postnatal rats, covering the main stages of development and eruption of the molar teeth. CRABPI positive cells were found in the mesenchymal cells of the dental follicle from the cap stage and in the dental papilla from the early bell stage. In the dental papilla, CRABPI positive cells were situated adjacent to the enamel organ in the cervical loop region and in the subodontoblastic region. Newly formed odontoblasts were CRABPI positive for a short period of time. The enamel organ was CRBPI and CRABPI negative, except for the presence of CRABPI positive cells in the internal enamel epithelium over the tip of cusps and in parts of the stratum intermedium. During root formation, CRABPI positive cells were found in the developing periodontal ligament, in the dental papilla adjacent to the epithelial root sheath and in the subodontoblastic zone. During crown formation, CRBPI positive cells were mainly localized to the mesenchymal cells of the dental papilla during the cap stage of crown development. The periosteum of the developing mandible contained CRABPI positive cells while some osteoclasts appeared to show a weak but positive reaction to CRBPI. The findings were considered in terms of the possible significance of retinoid-binding proteins during tooth and bone development.

In vitro effects of retinoic acid on mouse incisor development

The developing dentition is known to express the complete set of retinoic acid (RA) nuclear receptors and cytoplasmic RA-binding proteins (CRABPI and II), and RA is required for in vitro mouse molar morphogenesis, so the role of RA during in vitro mouse incisor development was investigated. Histological procedures, immunocytochemical detection of proliferating cells, immunofluorescence detection of laminin, and in situ hybridization with RNA probes for CRABPI and II were done on the tooth-germ cultures either in the presence or in the absence of RA. RA appeared to control initial morphogenesis, particularly the asymmetrical growth of the cervical loop, and to regulate required differential mitotic activity. RA seemed also to be involved in asymmetrical laminin deposition. The distribution of the CRABP gene transcripts was similar during in vivo and in vitro incisor development. However, CRABPI gene transcript distribution in the labial part of the epithelial loop was detected in vitro only in the presence of RA. A direct role of the CRABPs during tooth development is, however, unlikely because Ch55, a synthetic RA analogue that does not bind to CRABP, had the same effects as RA on in vitro incisor development.

Temporal distribution of endogenous retinoids in the embryonic mouse mandible

Retinoids play an important part in embryonic pattern formation. They are necessary for normal differentiation of odontogenic tissues and, in excess, disrupt the pattern of tooth formation. Excess retinoids produce supernumerary buds of the dental lamina in the diastema region of the mouse embryonic mandible where teeth do not normally form. This effect is coincident with an increase in epithelial proliferation and an alteration in epidermal growth factor mRNA expression (a gene product necessary for tooth formation). It was found by high-performance liquid chromatography that endogenous retinoids are present in the developing murine mandible and that concentrations of some retinoids reach a peak at the time of the initiation of odontogenesis (dental lamina formation).

Expression of nuclear retinoic acid receptors during mouse odontogenesis

The developmental expression of retinoic acid (RA) nuclear receptors RAR(alpha, beta, gamma) and RXR(alpha, beta, gamma) was analysed during mouse odontogenesis by in situ hybridization on frozen sections and compared with the expression patterns of the cellular retinoic acid binding proteins CRABPI and II. The transcripts distribution of each RAR and RXR was basically similar in developing molars and incisors. RAR alpha and RXR alpha were preferentially expressed in dental epithelia, whereas RAR gamma and RXR gamma were transcribed in the dental mesenchyme. RAR beta, RAR gamma and RXR beta displayed both epithelial and mesenchymal expression. RAR beta expression was initiated during bell stage. RXR gamma transcripts were observed only at day 19.5 post coitum in the mitogenic mesenchyme facing the epithelial loops. Odontoblasts expressed RAR beta and RAR gamma, RXR alpha and RXR beta. Preameloblasts expressed RXR alpha and RXR beta and ameloblasts RXR gamma, RXR alpha and RXR beta. RAR alpha transcription in the incisor preameloblasts and ameloblasts was not observed in the first molar. The coexpression between RARs and RXRs might be important to form RAR/RXR heterodimers which are necessary to activate the transcriptions of target genes. CRABPI and CRABPII demonstrated graded variation of expression during odontogenesis in the mesenchyme and in the inner dental epithelium respectively. The pattern of CRABPI transcripts overlapped at least partially with expressions of all the studied nuclear receptors whereas CRABPII epithelial expression was superimposed with the transcription of RAR alpha, RXR alpha and RXR beta. These cytoplasmic proteins might participate in the storage and/or metabolism of RA and then distribute RA to colocalized nuclear receptors.(ABSTRACT TRUNCATED AT 250 WORDS)