Effects of substrate texture and curvature on the morphology of cultured cells

The ultrastructural characteristics of several growth matrices were examined using two cell types chosen for their distinct growth habits. Chinese hamster ovary cells and Balb-c 3T3 mouse fibroblasts were grown on flat substrates (glass, tissue culture plastic, Millipore filters) as well as spherical (glass, tissue culture plastic, cross-linked dextran) substrates. Cells were plated maintaining equal densities and growth surface area. Once the majority of the cells reached confluency, the cell's morphology on each matrix was examined using scanning electron microscopy. Digital analysis was performed on cell attachment area to compare the effect of each matrix on cell spreading. Variation in cell shape was dramatic between matrices, being most noticeable between a textured surface (filter, dextran bead) and that of a smooth (glass) surface. Even within smooth surfaces, some variation was observed. There was also an effect of matrix curvature on cell attachment area, the greatest being in the 3T3-c Balb cells, causing an overall decrease in the area of attachment between cell and matrix. The changes seen could also be related to the particular cell type used. Hamster ovary cells tended to be cylindrical and showed little effect between matrices, whereas the mouse fibroblasts, which are more flattened, showed the matrix effect to a greater degree. This study demonstrates the necessity of being aware of substrate-induced cell changes in tissue culture, where some variation in cell shape may be due to the surface on which the cells are grown as opposed to the experimental procedure.

In situ embedding of cell monolayers cultured on plastic surfaces for electron microscopy

Various procedures suitable for routine in situ embedding of cell monolayers were tested including: (1) the use of different Epon substitutes, (2) the use of different types of plasticware obtained from different sources, and (3) different methods of preparing capsules for sectioning. Different resins reacted differently with different plastics and type of preparation. Merck Epon substitute bound to most of the plastics tested. Ladd Epon substitute released cleanly from all plastics tested when a suitable method of preparation was used. The results show that for routine embedding of cell monolayers it is necessary to select an appropriate Epon substitute and method of preparation of capsules for the type of plasticware used. A routine method is described, with various alternative steps which can be applied when particular difficulties are encountered.

Ultrastructure of a model basement membrane lacking type IV collagen

Basement membranes (BMs) are specialized extracellular matrices which have important roles in cell attachment, migration, growth, and differentiation. The major components of these matrices include type IV collagen, laminin, entactin, and heparan sulfate proteoglycan. The framework or scaffold of BMs has been proposed to be type IV collagen (Yurchenco et al., 1986, J. Histochem. Cytochem., 34:93-102). However, a murine teratocarcinoma cell-line, M1536-B3, has been described which produces an extracellular matrix (ECM) composed of some of the known components of BM, e.g., laminin, entactin, and sulfated proteoglycan, but lacking type IV collagen (Chung et al., 1979, Cell, 16:277-287). With the use of morphological techniques, we have found that the ECM assembled by these cells is composed of multiple layers of electron-dense cords arranged in an interweaving meshwork with short 2-4 nm-diameter cylindrical rods embedded throughout. This organization closely resembles that reported for naturally occurring BMs, e.g., Reichert's membrane (Inoué et al., 1983, J. Cell Biol., 97: 1524-1537). The previous identification of known in vivo BM components in M1536-B3 ECM and the correspondence in morphological appearance of M1536-B3 ECM with that present in naturally occurring BMs suggests that a BM-type of ECM can be assembled without a type IV collagen framework, thus indicating that other components of BMs have a critical role in BM organization and assembly.