Anchorage dependence and growth in suspension

Cell attachment and cell spreading are two related events but they are not necessarily controlled by the same factors. Attachment of cells to other cells or to a substrate occurs rapidly and may depend 

Primary cells will continue or start to divide in culture but exhibit contact inhibition of movement (Abercrombie and Heaysman, 1954). When two such cells approach one another the characteristic ruffling movements of the cell membrane stop in the area of contact. Primary cells therefore do not grow one on top of the other and, in general, cease to divide when a monolayer has been formed. This phenomenon is not restricted to primary cells but applies also to many cell lines. An ideal example is the 3T3 mouse fibroblast cell line which grows rapidly in sparse culture but all division stops as soon as the cells become confluent at about 106 cells per 6 cm dish (Holley and Kieman, 1968). Such cells may for some time remain 

As cells in a monolayer grow two changes occur (1) the cells become more crowded and less flattened and so expose a diminished surface area to the medium (2) the medium becomes depleted in nutrients etc., especially in a zone immediately surrounding the cells (Stoker, 1973). 

If a strip of cells is removed from a confluent monolayer of untransformed cells (e.g. 3T3 mouse embryo cells) then the cells at the edge of the wound are stimulated to synthesise DNA and divide. They quickly colonise the unoccupied area of the wound. This phenomenon known as topo inhibition (Dulbecco, 1970) is now explained by the presence in cells on the edge of the wound of an increased surface area exposed to the medium (i.e. neighbouring cells have been removed) (Stoker, 1973 Dulbecco and Elkington, 1973). 

The fact that crowded cells are less flattened and that cells in suspension are spherical and fail to grow, was followed up by Folkman and Moscona (1978) who showed that the extent of cell spreading was closely related to growth in non-transformed cells (Vasiliev, 1985). 

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