Scanning Electron Microscopy Volume 1986 Number 4 Article 32 10-1-1986 The Interface of Cells and Their Matrices in Mineralized Tissues: A Review S. J. Jones University College London A. Boyde University College London N. N. Ali University College London Follow this and additional works at: https://digitalcommons.usu.edu/electron Part of the Life Sciences Commons Recommended Citation Jones, S. J.; Boyde, A.; and Ali, N. N. (1986) "The Interface of Cells and Their Matrices in Mineralized Tissues: A Review," Scanning Electron Microscopy: Vol. 1986 : No. 4 , Article 32. Available at: https://digitalcommons.usu.edu/electron/vol1986/iss4/32 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Electron Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. SCANNING ELECTRON MICROSCOPY /1986/IV (Pages 1555-1569) 0586/5581/86$.00+0S SEM Inc., AMF O'Hare (Chicago), IL 60666-0507 USA THE INTERFACEOF CELLS ANDTHEIR MATRICES IN MINERALIZEDTISSUES: A REVIEW S. J. Jones; A. Boyde and N. N. Ali Dept of Anatomy and Embryology, University College London, London WClE 6BT, UK (Received for publication May 09, 1986, and in revised form October 01, 1986) Introduction Abstract Hard tissues are unique in that their The interface between cells and matrices in calcified matrix has a relatively undistortable mineralized tissues formed in vivo has been form that is not dependent on the presence of the studied mainly by looking at the matrix surface, cellular or water component. The fit of the which is easily prepared, and not at the eel l surface of the matrix to the cells that form it, surface, which presents problems. Vertebrate maintain it, or resorb it is precise. The calcified tissues range from being acellular to matrix, therefore, constitutes a replica which highly cellular, but for all the tissues the can tell us much about the physiological status formative cells lay down and organise a cell­ of the tissues even once the cells have been specific matrix, although this may be deposited removed. The hard tissue matrices contain less initially on a different tissue-type. The water than cells, and may shrink and distort less formation of hard tissues is a group activity of than other types of sample in preparation for SEM many cells; resorption is the province of one study. cell, though it may be controlled by others in Formation and resorption of hard tissues are the vicinity. surface phenomena,and the physicochemical nature Cell-matrix interfaces that develop in vitro of the interface between the cells and the tissue have also mainly been studied at the matrix side. below that is their product or target is one The main difficulty with in vitro studies of hard factor that controls eel l ul ar activity. Interest tissue interfaces is that the eel ls do not have in cell-matrix interactions has grown lately as the same activity or even cellular functions as research workers in all fields have begun to they had in vivo under the complex control of discover how great is the interplay between the physiological regulation. The question of two in the embryology, construction, maintenance osteoblastic osteoclasis falls into this categor~ and destruction of tissues. We are especially It is possible to provide new substrata for fortunate in that hard tissues grow both formative and resorptive hard tissue cells appositionally rather than interstitially, so to test for the interaction between the cells and that the history of the development of the tissue the 'matrix' on to which they are seeded. The is fossilised and the incremental pattern is changing cell-matrix interface may also be available to us at a later time. The low modelled using computer simulation of turnover rate of mineralized tissues, or its osteoclastic movement across a substrate based on absence, increases the recorded data available known patterns exhibited by other eel l types in for our interpretation. vitro. Comparison with the shapes of complex Some hard tissues such as enamel and resorption pits shows a surprising match, This acellular cement, have surfaces only at their suggests that the track of the osteoclast due to outer boundaries; others also have internal cell cell motility and the bone resorptive mechanism matrix surfaces, for example, dentine, cellular resulting in pits along that track are likely to cement and calcified cartilage; a third category be separately controlled phenomena. such as mammalian bone, vasodentine and vasocementum, and cartilage with vasocanals, have, in addition, vascular channels Key words: Bone disease,dentine, enamel, cement, incorporated in the tissue. cartilage, formation, resorption, osteobl asts, The markings that are left embedded in the osteoclasts, ameloblasts, chondroblasts, SEM. tissue as a result of past cell activity, and the cell-intercellular matrix or cell-matrix surface *Address for Correspondence: Sheila J. Jones imprints or interfaces provide the scanning Department of Anatomy and Embryology electron microscopist with a wealth of data from University College London, London WClE 6BT, UK. which to assess physiological and pathological Telephone: 01 387 7050 Ext.3319 aspects of mineralized tissues. 7555 S.J. Jones, A. Boyde and N.N. Ali 1556 CELL-MATRIXINTERFACE figure l. Osteoblasts, osteoid, and bone in shaping the surface and control ling the containing osteocytes in rat cal varium. Fixed assembly and orientation of the macromolecules glutaraldehyde and osmium, ethanol freeze within it. The secretory territory of one eel 1, fractured - and CPD. Fieldwidth = lBµm. or the shape of its secretory pole, will change figure 2. Odontoblasts separated from their with alterations in the rate of matrix predentine matrix in rat incisor, fixed in 2% deposition. Nevertheless, although in some Os □ 4 in boric acid borate buffer, CPD and dry tissues, such as enamel, the individual cellular dissected; showing parts of the cells which were footprints are clearly defined (Fig.3), for most in contact with their shared product, predentine. connective tissues it is the functioning patch Fieldwidth = 64µm. of cells that is important in structuring the figure 3. Surface of enamel matrix in anorganic, matrix (Boyde, Reith and Jones, 1977), and they freeze-dried human deciduous incisor. The work together (Fig. 4). The amount and depressions in this surfaces were made by organisation of matrix produced may reflect the secretory pole processes of the formative cells, response of groups of cells to local ameloblasts. Fine structure in the surface shows requirements, in the case of skeletal tissues and growth of ice crystals at the frozen stage. reparative dental tissues, or be graded according There are also depressions made by secondary to the temporospatial location of cells in an processes of the main cell process. Fieldwidth = incremental layer, such as when dental tissues 37JJm. develop in a tooth (Jones and Boyde, 1984: Figure 4. Surface of bone matrix of rat Fig.5), or bone is formed in an osteonal closing cal varium after removal of osteoblasts, leaving cone. one future osteocyte in its half formed lacuna at the surface. It is not possible to distinguish The interface between cells and the matrix they the parts of the matrix made by individual cells. have formed Fieldwidth = 69,um. Figure 5. External surface of a developing human This surface has the organic matrix and molar showing the deposition of enamel on fhe mineral surfaces coincident: no unmineralized surface of dentine matrix (bottom half of field) matrix remains . The matrix has, therefore, a illustrating temporo-spatia l gradation of eel l robust interface with the eel ls and this can be differentiation and of tissue development. exposed with little or no damage. It tel ls us Fieldwidth = 9lµm. about what has happened, but little or nothing figure 6. Resorption-formation coupling of cement about what would have happened next, particularly on enamel in a horse molar tooth. The completed in calcified connective tissues like bone where enamel surface is resorbed by osteoclasts; then formation may stop, only to start again later, or repaired by cementum. Fieldwidth = 20Qum. be followed by resorption. There is, of course, an intermediate stage, where matrix formation has stopped, but mineralisation has not yet reached the surface. The interface between secreting cells and the This unmineralized matrix may be mature enough to matrix they are forming resist solution, and less susceptible to shrinkage artefacts because of its lower water The matrix components that a hard tissue content. forming cell secretes assemble outside the cell, At both forming and formed interfaces, the changing their size and relative proportions as cell and its matrix are matched: for example, the the tissue matrices mature prior to or during ameloblast makes and reacts with enamel; the mineralization. Some proteins, small peptides osteoblast the same with bone, whether the cells and glycosaminoglycans may be soluble and lost are actively secreting or have ceased to do so. from the surface layer during specimen handling However, formative cells also interact with for SEM. They can also be distorted during dissimilar matrices. For example, enamel is drying, for the water content of most of the deposited by ameloblasts on dentine matrix (Fig. matrix immediately next to the secretory pole of 5), osteoblasts form bone on calcified cartilage, the eel l is relatively high (Fig l ). The depth of and cementoblasts form cementum on enamel (Fig. this vulnerable layer will be greatest where the 6). Nevertheless, the tissue formed is secretory rate is highest, and minimal after characteristic of the cell type, not the temporary or complete cessation of secretion as underlying tissue that stimulated new matrix the surface tissue has an opportunity to mature. deposition by the eel l. The tissue at the Another factor of importance will be the extent interface becomes cell-specific and cell of the interdigitation of the secreting cells organized.