Role of the cytoskeleton in the reaction of fibroblasts to multiple grooved substrata

Reactions of cells to topography

Though contact guidance has been known since the very early days of cell culture very little quantitative examination of the reaction of cells to topography has been made. Exceptions to this subjective approach are given prominence below. Yet if we are to understand how cells react and if we are to be able to design ideal substrata for particular cells we need this information. Precision and quantitation are required both of the methods of examination of the cells but also in the definition of that topography. Recently it has become clear that the these reactions occur at the nanometric scale and have importance for use in cellular engineering and tissue repair. Topography appears to provide a set of very powerful signals for cells.

Surface topography can interfere with epithelial tissue migration

Corneal epithelial tissue migration over the surface of a synthetic polymer can be inhibited by pores in the substrate. The effects of this substrate topography upon epithelial tissue migration were studied in vitro. Membranes of different porosities and structures were used to provide two series of surfaces having a graded increase in discontinuities: cellulose nitrate/acetate membranes with a tortuous network of pores, and track-etched polycarbonate membranes with columnar pores. Corneal epithelial tissue outgrowth was inhibited by increased pore size, and for both series of membranes, outgrowth was completely halted on membranes with mean diameter of the pores 0.9 microm at the pore densities measured. On the track-etched membranes with pores of <0.9 microm diameter, tissue outgrowth could be partially "rescued" by coating with fibronectin or collagen, but above this size, the inhibition predominated. The effect of porosity of the track-etched membranes upon the migration of dissociated epithelial cells was also examined. Although migration of these cells was reduced on membranes having pore sizes larger than 0.9 microm, it was not completely inhibited even on membranes of 2.3-microm pore diameter. Therefore, tissue movement of adult stratified epithelium may be inhibited by specific surface topographies, and in this assay system, epithelial tissue outgrowth was more affected than was the migration of dissociated epithelial cells.

Sensitivity of fibroblasts and their cytoskeletons to substratum topographies: topographic guidance and topographic compensation by micromachined grooves of different dimensions

Fibroblasts alter their shape, orientation, and direction of movement to align with the direction of micromachined grooves, exhibiting a phenomenon termed topographic guidance. In this study we examined the ability of the microtubule and actin microfilament bundle systems, either in combination with or independently from each other, to affect alignment of human gingival fibroblasts on sets of micromachined grooves of different dimensions. To assess specifically the role of microtubules and actin microfilament bundles, we examined cell alignment, over time, in the presence or absence of specific inhibitors of microtubules (colcemid) and actin microfilament bundles (cytochalasin B). Using time-lapse videomicroscopy, computer-assisted morphometry and confocal microscopy of the cytoskeleton we found that the dimensions of the grooves influenced the kinetics of cell alignment irrespective of whether cytoskeletons were intact or disturbed. Either an intact microtubule or an intact actin microfilament-bundle system could produce cell alignment with an appropriate substratum. Cells with intact microtubules aligned to smaller topographic features than cells deficient in microtubules. Moreover, cells deficient in microtubules required significantly more time to become aligned. An unexpected finding was that very narrow 0.5-microm-wide and 0.5-microm-deep grooves aligned cells deficient in actin microfilament bundles (cytochalasin B-treated) better than untreated control cells but failed to align cells deficient in microtubules yet containing microfilament bundles (colcemid treated). Thus, the microtubule system appeared to be the principal but not sole cytoskeletal substratum-response mechanism affecting topographic guidance of human gingival fibroblasts. This study also demonstrated that micromachined substrata can be useful in dissecting the role of microtubules and actin microfilament bundles in cell behaviors such as contact guidance and cell migration without the use of drugs such as cytochalasin and colcemid.

After embryonic day 17, distribution of cells on surface of primary muscle fibres in mouse is non-random

During the formation of skeletal muscle, secondary fibres form, by cell fusion, on the surface of primary fibres. Three-dimensional reconstructions of primary fibres with the secondary fibres and cells on their surfaces were produced from spaced serial transmission electron micrographs. Reconstructions were made of fibres from embryonic day (E) 17, E19, and E21 of the Extensor Digitorum muscle of Balb/c mice. Cell distribution was analysed in two ways. Firstly, nearest neighbour analysis was used to see if cells were randomly arranged or clustered. Secondly, the association of cells and secondary fibres was tested by measuring the distances between cells and each secondary fibre. Cells were found to be randomly distributed on the surface of primaries at E17 but significantly clustered, and associated with smaller secondary fibres at E19 and E21. Cells were not associated with the ends of secondary fibres. Cells associated with secondary fibres lay in the groove formed by contact between adjacent primary and secondary fibres. This apparent response to the topography of the surface on which the cells are lying has previously been mimicked in vitro by growing cells on grooved surfaces. It is likely that cells associated with secondaries will fuse laterally with these fibres and their response to topography is part of the process of bringing them into correct alignment with the fibre before fusion.

After embryonic day 17, distribution of cells on surface of primary muscle fibres in mouse is non-random

During the formation of skeletal muscle, secondary fibres form, by cell fusion, on the surface of primary fibres. Three-dimensional reconstructions of primary fibres with the secondary fibres and cells on their surfaces were produced from spaced serial transmission electron micrographs. Reconstructions were made of fibres from embryonic day (E) 17, E19, and E21 of the Extensor Digitorum muscle of Balb/c mice. Cell distribution was analysed in two ways. Firstly, nearest neighbour analysis was used to see if cells were randomly arranged or clustered. Secondly, the association of cells and secondary fibres was tested by measuring the distances between cells and each secondary fibre. Cells were found to be randomly distributed on the surface of primaries at E17 but significantly clustered, and associated with smaller secondary fibres at E19 and E21. Cells were not associated with the ends of secondary fibres. Cells associated with secondary fibres lay in the groove formed by contact between adjacent primary and secondary fibres. This apparent response to the topography of the surface on which the cells are lying has previously been mimicked in vitro by growing cells on grooved surfaces. It is likely that cells associated with secondaries will fuse laterally with these fibres and their response to topography is part of the process of bringing them into correct alignment with the fibre before fusion.