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M MacDougall

Publications and source records attributed to M MacDougall.

70 records · Page 4Linked to original sources
PubMed1988

Factors influencing the expression of dental extracellular matrix biomineralization.

The forming tooth organ provides a number of opportunities to investigate the cellular and molecular biology of cell-mediated extracellular matrix (ECM) biomineralization. Regulatory processes associated with tooth formation are being investigated by identifying when and where cell adhesion molecules (CAMs), substrate adhesion molecules (SAMs), dentine phosphoprotein and enamel gene products are expressed during sequential developmental stages. In vitro organotypic culture studies in serumless, chemically-defined medium, have shown that instructive and permissive signalling are required for both morphogenesis and cytodifferentiation. Intrinsic developmental instructions (autocrine and paracrine factors) act independently of long-range hormonal or exogenous growth factors and mediate morphogenesis from the initiation of the dental lamina to the crown stages of tooth development. This review summarizes the results of studies using experimental embryology, recombinant DNA technology and immunocytology to elucidate mechanisms responsive to instructive epithelial-mesenchymal interactions associated with ameloblast differentiation, odontoblast differentiation, and dentine and enamel ECM biomineralization.

Animals↗
PubMed1988

Molecular determinants of cranial neural crest-derived odontogenic ectomesenchyme during dentinogenesis.

Positional information on tooth morphogenesis is investigated by the identification of when and where phenotypic markers are expressed during odontogenesis. This temporal and positional information is correlated with the instructive and permissive signaling required for both dentinogenesis and amelogenesis. Of particular interest is the establishment of a map for the cranial neural crest-derived dental papilla ectomesenchyme and the odontoblast cell lineages. The expression of ectomesenchyme-derived cytotactin, dentin phosphoprotein, and epithelial-derived enamel proteins was studied in mice using embryonic, fetal, and postnatal mandibular first molar tooth organ development. This review summarizes the observations in the context of instructive epithelial-mesenchymal interactions and suggests that amelogenesis imperfecta and dentinogenesis imperfecta may in part be explained by alterations in these differentiation markers. Recombinant DNA methods should facilitate future investigations of these inherited dental disorders.

Animals↗
PubMed1987

Immunochemical and biochemical studies of human enamel proteins during neonatal development.

The present communication provides descriptions of the developmental, biochemical, and immunological properties of the human enamel extracellular matrix proteins. We report the isolation and partial characterization of the major human enamel proteins, the production of polyclonal antibodies directed against the human enamelins, and a comparison between the immunogenicity of enamelins and amelogenins from human and mouse enamel extracellular matrices. Our results indicate that although enamelins and amelogenins share some epitopes, each one of these proteins appears to invoke a different degree of immunogenicity.

Amelogenin↗
PubMed1985

Production and characterization of antibodies against murine dentine phosphoprotein.

Experiments were designed to produce and characterize a polyclonal antibody directed against mouse dentine phosphoprotein, the major non-collagenous protein of the dentine extracellular matrix. Dental extracellular matrix proteins from 2-day-postnatal Swiss-Webster-mouse tooth organs were extracted with 0.5 M-acetic acid, followed by 4 M-guanidinium chloride/0.5 M-EDTA. Mouse dentine phosphoprotein yields were further increased by precipitation with 1 M-CaCl2. Final purification was achieved by excising and eluting dentine phosphoprotein polypeptide bands from preparative sodium dodecyl sulphate/urea/polyacrylamide gels. Mouse dentine phosphoprotein is a single component of approx. 72 kDa and has a characteristic amino acid composition of 33% aspartic acid and 55% serine/phosphoserine. A polyclonal antibody was raised in rabbits against purified mouse dentine phosphoprotein and was shown to be monospecific by enzyme-linked immunoabsorbent, dot-immunobinding and 'Western transfer' assays. This antibody was used to detect the expression and localization of dentine phosphoprotein in 1-day-postnatal mouse tooth organs. This antigen was localized intracellularly within the monolayer of odontoblasts, which line the perimeter of the dental papilla mesenchyme, and within the odontoblastic cell processes, which traverse the predentine matrix. Newly forming mineralized dentine matrix was also cross-reactive with the dentine phosphoprotein specific antibody. The non-mineralized predentine matrix did not contain any detectable cross-reactive antigens.

Amino Acids↗
PubMed1983

Enamelin gene expression during fetal and neonatal rabbit tooth organogenesis.

Epithelial differentiation is a complex process which requires an integrated synthesis of DNA along with synthesis of a full complement of unique mRNAs and their respective proteins characteristic for each cell type. The time of initial transcription of enamel protein mRNAs and subsequent translation of proteins characteristic for secretory ameloblasts is not known. In order to determine when enamel protein mRNAs appear during New Zealand White rabbit molar tooth organogenesis, and when nascent enamel proteins are first translated, we analyzed early cap stages through late crown stages of molar tooth formation (i.e., 21-days gestation through 2-days postnatal). The biochemical phenotype which characterized rabbit ameloblasts were the acidic glycoproteins termed enamelins. Polyclonal antibodies were produced against the major fetal rabbit enamelin of approximately 70,000 daltons. Immunoprecipitation of enamelins from mRNA-directed translation products in a reticulocyte cell-free system, was used to characterize enamelin mRNAs. Enamelin mRNAs were first detected during bell stages (circa 23-days gestation), and persisted till crown stage (circa 28-days gestation). Indirect immunofluorescent localization of enamelin antigen showed staining over the extracellular enamel organ matrix by 23-days gestation. Neither enamelin mRNAs or polypeptides were detected during early or late cap stages of odontogenesis. Transcription of enamelin mRNAs coding for two enamelins of 65 an 58 kd (kilodaltons) appeared to be closely coupled with the translation of these enamel proteins. We assume that close-range ectomesenchyme- derived instructions mediate the biochemical differentiation of ameloblasts between 21-days and 23-days gestation during fetal rabbit development.

Ameloblasts↗
PubMed1983

Basal lamina persistence during epithelial-mesenchymal interactions in murine tooth development in vitro.

Numerous investigations have demonstrated the necessity of mesenchymal instruction for epithelial differentiation during epidermal organogenesis. In the specific case of tooth formation, cap-stage tooth organ mesenchyme instructs epithelial differentiation into ameloblasts with production of enamel extracellular matrix. The "instructive event" is presumed to be direct cell contact. Mesenchyme-mediated cell contact with adjacent epithelia is assumed to "instruct" epithelial differentiation into ameloblasts. If this were true, basal lamina removal and mesenchyme cell contact with epithelia would be prerequisites for epithelial cytodifferentiation and morphogenesis in the developing tooth system. To test this hypothesis, we designed experiments to evaluate basal lamina stability during epithelial differentiation into ameloblasts. Our studies utilized cap-stage murine molar tooth organs, a serumless and chemically defined medium (PYMS), metabolic isotopic labeling of basal lamina constituents, biochemical methods to analyze macromolecular stability throughout 10 days of organ culture in vitro, and immunological methods to localize the distribution of laminin and fibronectin. Our results indicate that (3H)glucosamine is incorporated into basement membranes present in Theiler stage 25 mandibular mouse molar tooth organ. At this stage, the isotope was incorporated into high molecular weight macromolecules. Specific enzyme methods coupled with electrophoresis and fluorography demonstrated that (3H)glucosamine was incorporated into proteoglycans containing chondroitin sulfates, dermatan sulfate, and hyaluronate. After 10 days in vitro the radiolabeled material remained localized in these same molecules, indicating stability of these constituents within basement membranes. Ultrastructural observations indicated that the basal lamina was not removed during ameloblast differentiation in vitro using PYMS medium. Laminin and fibronectin were localized in the basement membranes during cap stages and did not disappear during subsequent morphogenesis and differentiation. Mesenchymal cells appear to mediate epithelial differentiation in vitro using PYMS medium without a removal of the basal lamina.

Animals↗
PubMed1982

Enamel gene products during murine amelogenesis in vivo and in vitro.

Epithelial-mesenchymal interactions regulate determination and differentiation of amelogenesis. Our attention has focused on identification of ameloblast gene products, the regulation of enamel mRNA synthesis, and subsequent translation into enamel proteins in vivo and in vitro. Enamel proteins are the most abundant gene products synthesized in fully-differentiated ameloblasts. Our experimental strategy has been to isolate major proteins, produce antibodies, localize enamel protein antigens during tooth development in vivo as well as in vitro (using serumless, chemically-defined medium), develop an immunoprecipitation assay, isolate poly(A)-products in a cell-free translation system, and then initiate molecular cloning of the corresponding murine enamel gene(s). The major murine enamel mRNA appears to code for a predominant polypeptide of approximately 20,000 MW. Inner-enamel epithelial cells differentiate into ameloblasts, and synthesize and secrete enamel proteins within six d when cap-stage molar tooth organs are cultured in serumless, chemically-defined medium. The regulation of epithelial differentiation under these experimental conditions indicates that epithelial-mesenchymal interactions determine and maintian ameloblast differentiation in vitro.

Ameloblasts↗
PubMed1981

Spatiotemporal patterns of fibronectin distribution during embryonic development. I. Chick limbs.

It has been suggested that an extracellular matrix - and cell surface - associated glycoprotein, fibronectin, plays a role in the positioning of cells in morphogenesis and in the maintenance of orderly tissue organization. In the present study the appearance and distribution of fibronectin during in ovo chick limb development has been investigated by indirect immunofluorescence techniques in H.H. stages 20-30. Fibronectin is not detectable until just prior to the transition from the morphogenetic to the cytodifferentiation phase of development. Beginning at H.H. stage 25, successive nonrandom patterns of fibronectin detection and distribution, which resemble the subsequent cartilaginous elements, precede overt chondrogenesis as detected by Alcian blue staining. This corresponds to the onset of the cytodifferentiation phase of limb development. As the accumulation of acidic proteoglycan increases in the cartilage matrix and the mesenchymal cells become more round in appearance, the presence of detectable fibronectin decreases and is ultimately seen only in the perichondria and basement membrane. However, predigestion of developed cartilage tissue with testicular hyaluronidase, prior to fibronectin staining, indicated that fibronectin remains a major constituent of cartilage matrix and is apparently masked by cartilage-specific proteoglycans. This study of chick limb development is consistent with the hypothesis that fibronectin may be a molecule that facilitates the spatial organization of cartilaginous primordia cytodifferentiation.

Animals↗
PubMed1981

Spatiotemporal patterns of fibronectin distribution during embryonic development. II. Chick branchial arches.

It has recently been demonstrated with the chick limb in ovo that successive nonrandom patterns of fluorescent staining with specific antibodies to fibronectin indicate the cartilagenous primordia prior to overt chondrogenesis. Given the apparent nonequivalence of embryonic cartilages, the purpose of this study was to determine whether this phenomenon was unique to developing chick limbs or is a more general characteristic of chondrogenesis. The appearance and distribution of fibronectin during chick first and second branchial arch development in ovo was investigated by indirect immunofluorescence techniques in H.H. stages 15-26. Fibronectin can be detected in early stages in areas presumed to be composed mainly of ectomesenchyme. During later stages of development, successive nonrandom patterns of fibronectin distribution appear to precede overt chondrogenesis as demonstrated by alcian blue staining. Pretreatment of cartilage with testicular hyaluronidase, prior to fibronectin staining, revealed that fibronectin was still present, suggesting that it was masked by proteoglycans. Fibronectin was also detected in the developing membrane bones of the mandible. The nonrandom patterning of fibronectin distribution in ovo in chick branchial arches and limb buds, respectively derived from neural crest and somatic mesoderm, were similar. It appears that specific patterns of fibronectin distribution were characteristic of chondrogenesis, regardless of the embryonic origin of the cartilage. This phenomenon may prove to be an extremely useful probe for early developmental skeletal abnormalities.

Animals↗
PubMed1980

Chemically-defined organ culture of embryonic mouse tooth organs: morphogenesis, dentinogenesis and amelogenesis.

Chemically-defined in vitro conditions without serum have been identified which are permissive for embryonic mouse tooth organs to express morphogenesis and cytodifferentiation. In the absence of antibiotics, embryonic extracts, autologous and/or heterologous sera, molar tooth organs from Theiler stage 25 embryos (C57BL/6, A/Jax and Tabby mouse strains) routinely formed discrete dentin and enamel extracellular organic matrices within 10 days of continuous in vitro cultivation. Collagen and non-collagenous protein synthesis and secretion by differentiated cells within explants, between 9 and 10 days in vitro, were studied with light microscopic autoradiography. Finally, explants of embryonic mouse molar tooth organs have been maintained in organ culture for three week without serum supplementation.

Amelogenesis↗
PubMedDate not supplied

Presence of dentin phosphoprotein in molars of a patient with dentinogenesis imperfecta type II.

Dentin phosphoprotein (DPP) is the major noncollagenous protein component of the dentin extracellular matrix. This highly acidic phosphorylated protein is solely expressed by the ectomesenchymal-derived odontoblast cells of the tooth organ. Several biochemical studies have suggested diminished levels of, or even the absence of, this protein, which is associated with the human genetic disease dentinogenesis imperfecta (DGI) type II. However, more recent molecular studies have established that the DPP gene locus is not localized to the region of human chromosome 4 (4q13-q21), where several previous linkage analysis studies have mapped DGI types II and III. The purpose of this study was to determine the presence or absence of DPP in the dentition of a patient affected with DGI type II using a sensitive and specific immunodetection method with a polyclonal antibody against mouse DPP. Our results indicate that a 95-kDa protein, immunologically crossreactive with the DPP antibody, was detected within the dentin extracellular matrix of molars isolated from both a proband affected with DGI-II and from an age-matched normal individual. In addition, both DGI-II and normal individuals showed comparable DPP in situ degradation associated with dentin extracellular matrix maturation. These results strongly support the hypothesis that the DPP structural gene does not produce the gene product primarily responsible for the human genetic disease DGI type II.

Adult↗