Embryonic Tooth Germs Research Articles

Short-Term Mineralization of Dentin and Enamel in the Mouse Embryonic Molars Cultured in Serum-Free, Chemically-Defined Medium.

The present study was designed to demonstrate the short term mineralization of dentin and enamel, and to investigate the effects of sodium beta-glycerophosphate (Na-beta-GPO4) on calcification in a serum-free, chemically-defined medium. The first mandibular molars at the bell stage dissected from 18-day-old mouse embryos were used as explants, which were cultured by an improved flotation method. Calcification of enamel in the 18-day-old embryonic molars occurred within the 6th day of culture. In another experiment, the molar germs were cultured in a serum-free, chemically-defined medium supplemented with 1, 5 and 10 mM Na-beta-GPO4. Promotion of tooth mineralization was recognizable at very low concentrations, such as 1 mM Na-beta-GPO4, in 18-day-old embryonic tooth germs. The culturing system reported here shortens the time required for dentin and enamel calcification to one half or one third of that reported previously and therefore should prove useful for examining regulations for cytodifferentiation and morphogenesis in tooth germs and the mineralization of dentin and enamel.

Growth factors and tooth development.

The effects of various growth factors on tooth development were studied in organ cultures of mouse embryonic tooth germs. Transferrin was shown to be a necessary growth factor for early tooth morphogenesis. Transferrin was required for the development of bud- and early cap-staged teeth, and it was shown to be the only serum protein that was needed by early cap-staged teeth in organ culture. Promotion of tooth morphogenesis and dental cell differentiation was shown to be based on the stimulation of cell proliferation. The roles of polypeptide growth factors in tooth development were studied by adding these factors to the transferrin-containing chemically-defined culture medium which supports early tooth morphogenesis and cell differentiation. Fibroblast growth factor or platelet-derived growth factor did not affect cell proliferation or morphogenesis of tooth germs in culture. On the contrary, epidermal growth factor (EGF) stimulated cell proliferation in tooth explants, but at the same time inhibited tooth morphogenesis and dental cell differentiation. Autoradiographic localization of proliferating cells revealed that dental tissues responded to EGF with different proliferation rates. The responsiveness to EGF was stage-dependent, early cap-staged teeth were sensitive to EGF but late cap-staged and bell-staged teeth developed normally in the presence of EGF in the culture medium. The presence and distribution of receptors for both transferrin and EGF were studied in mouse embryonic teeth at various developmental stages by incubating freshly-separated tooth germs with 125Iodine-labeled transferrin or EGF, and then processing the tissues for autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcriptional activity in lysates of cultured mesenchymal cells from embryonic tooth germs.

Mesenchymal cells isolated from the papilla of embryonic tooth germs of the mouse were cultured in a complex medium for five to six days. Liquid nitrogen lysates, prepared from these cells, incorporated nucleoside monophosphates into a cold acid-insoluble product. The product was sensitive to RNase and no product was formed if the lysate was pretreated with DNase. The reaction was sensitive to EDTA and, in its presence, optimum activity was obtained with 2 mM MgCl2. On sucrose gradients, the reaction product was distributed between two broad peaks; one centered about 18S and the other above 28S. The RNA polymerase inhibitor alpha-amanitin inhibited approximately 50% of the activity at a concentration of 10 microgram/ml.

In vitro utilization of exogenous procollagen by embryonic tooth germs

Embryonic mouse tooth germs treated with L-azetidine-2-carboxylic acid cease their development, undergo a regression of the enamel organ, and do not maintain the histological characteristics of the explanted dental organ. On the other hand if procollagen is added exogenously to explants continously treated with L-azetidine, the effects of the inhibitor are not seen and the tissue is maintained. Thus, exogenously supplied procollagen supports morphogenesis in tooth rudiments that are unable to synthesize procollagen.

The fine structure of the extracellular matrix during epithelio-mesenchymal interactions in the rabbit embryonic incisor.

AbstractThe fine structure of the extracellular matrix during epithelio‐mesenchymal interactions in the rabbit embryonic tooth germ is described using light and electron microscopy. Observations are restricted to the labial cervical loop region at the bell stage of development in maxillary and mandibular incisor tooth germs. Histochemical methods demonstrate a PAS‐positive basement membrane between outer enamel epithelial cells and adjacent undifferentiated mesenchymal cells. The metachromatic region circumscribes the dental papilla region, becoming more intense and wider in association with cells illustrative of more advanced stages of differentiation. Ultrastructural observations of the basal lamina associated with outer enamel epithelial cells, cervical proliferating epithelial and mesenchymal cells, and with inner enamel epithelial cells and pre‐odontoblasts are reported. The characteristic mesenchymal filopodia appeared in close proximity to the basal lamina. Microfibrils are seen as depositions on the basal lamina and in association with filopodia. The concentration of intercellular microfibrils is increased when in association with epithelia showing advanced differentiation. Collagen fibrils are frequently noted in peripheral association with mesenchymal cells but not adherent to the basal lamina. Numerous homotypic and heterotypic cell junctions are seen. An understanding of intercellular communication between heterotypic cells may be enhanced by postulating a dual developmental origin for the microfibrils associated with the basal lamina. The under surface of the basal lamina facing the extended mesenchymal filopodia appears to be a significant factor during epithelio‐mesenchymal interactions, subsequent extracellular matrix formation, and morphogenesis.