Biomedical subjects
K Hurmerinta
Publications and source records attributed to K Hurmerinta.
The cellular origin of fibronectin in the basement membrane zone of developing tooth.
The cellular source of fibronectin in the dental epitheliomesenchymal interface was studied in interspecies combinations of mouse and quail tissue. Species-specific fibronectin antibodies were produced by immunizing rabbits with purified mouse or chicken fibronectin and by absorbing both antisera with purified heterologous fibronectin and insoluble tissue extract. The absorbed antisera to mouse and chicken fibronectin showed fluorescent staining only in mouse and chicken tissue sections, respectively, but not vice versa. When the mouse mesenchymal dental papilla was combined and cultured either with the mouse enamel organ or with the quail pharyngeal epithelium, mesenchymal cell differentiation was initiated and typical alignment of mesenchymal cells along the basement membrane was seen. Examination with transmission electron microscope revealed a typical bilaminar basal lamina with adherent fibrillar matrix on its mesenchymal aspect. Immunofluorescent localization of fibronectin with the mouse-specific fibronectin antiserum showed a brilliant staining in the mesenchymal tissue and in the basement membrane zone. When the chicken-specific fibronectin antiserum was used, no staining was detected in either tissue recombinations. We have suggested earlier that fibronectin in the dental basement membrane plays an important role during the differentiation of mesenchymal cells into odontoblasts. The present study demonstrates that fibronectin in the basement membrane of the developing tooth is produced exclusively by the differentiating mesenchymal cells.
[Cell interactions in early tooth development].
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Diazo-oxo-norleucine (DON)-induced alterations in the extracellular matrix of the mouse tooth germ.
In a previous study we have shown that the glutamine analogue diazo-oxo-norleucine (DON) inhibits the differentiation of mesenchymal cells into odontoblasts in the developing tooth. In the present study we have studied the effect of DON on the formation of the extracellular matrix by using light microscopic autoradiography and transmission electron microscopy. The inhibition of odontoblast differentiation was accompanied by alterations in the extracellular matrix at the epithelio-mesenchymal interface. The interface was reduced in space and filled with filamentous material, and the organization of collagen fibers in more advanced tooth germs was disturbed. DON also reduced the incorporation of [35S]sulphate into the basement membrane region, whereas no marked change was observed in the incorporation of [3H]fucose. These results suggest that DON affected the cell--matrix interaction which is believed to control the differentiation of odontoblast.
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.
Cell interactions during tooth development.
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Tissue interactions in tooth development.
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Ultrastructure of the epithelial-mesenchymal interface in the mouse tooth germ.
The structure of the epithelial-mesenchymal interface of a developing mouse embryonic tooth germ was examined at the time of cell differentiation by using transmission and scanning electron microscopy. During odontoblast differentiation, the basal lamina was continuous beneath the inner enamel epithelium, and the fibrils at the mesenchymal aspect increased in density and length. Numerous cell processes of the preodontoblasts were seen in close contact with the basal lamina. This supports the idea that the basement membrane is involved in the differentiation of mesenchymal cells into odontoblasts, probably by providing special attachment sites for the aligning mesenchymal cells. The rearrangement of intracellular organelles in the cells of enamel epithelium and a change of epithelial morphology were already seen at the time of the initial predentin secretion by odontoblasts. At this time, the basal lamina was still present. The penetration of epithelial microvilli into the epithelial-mesenchymal interface through breaks in the basal lamina related to the onset of predentin mineralization. This suggests that the determination of epithelial cells into ameloblasts already occurs before the disappearance of the basal lamina.
In vitro inhibition of mouse odontoblast differentiation by vitamin A.
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Inhibition of tooth germ differentiation in vitro by diazo-oxo-norleucine (DON).
Molar tooth germs from mouse embryos were studied in a Trowell-type organ culture. After 5 days of culture the odontoblasts had secreted predentine and the ameloblasts had differentiated. When cultured in the presence of 10-50 micro M diazo-oxo-norleucine (DON), which is a glutamine analogue, the differentiation of odontoblasts was inhibited, but the teeth looked otherwise healthy. When DON was added after 2 days of culture in control medium (at this time the odontoblasts in the cuspal area were already differentiated), it did not inhibit predentine secretion, ameloblast differentiation, nor enamel secretion. However, this was seen only in the cuspal area and the boundary to the undifferentiated, more cervical cells was distinct. The results support the concept that the mechanism of the differentiation of odontoblasts is different from that of the ameloblasts. We have shown earlier that a close association between the basement membrane and the mesenchymal cells is required for odontoblast differentiation. Because DON interferes with glycosaminoglycan and glycoprotein synthesis we suggest that DON inhibits odontoblast differentiation by affecting the mesenchymal cell surface and/or the basement membrane.