Interaction of rat Sertoli cells with a collagen lattice in vitro.

Sertoli cells from rats aged 15, 20, and 25 d were subcultured onto collagen-coated, plastic dishes. If the collagen was released from the plastic surface by rimming, the floating rafts of collagen showed uniform shrinkage. If the collagen was allowed to remain attached to the plastic, holes appeared in the collagen with cells from rats aged 25 d but not with those of 15 d. Cells from rats aged 20 d caused fewer and smaller holes to appear. The holes were associated with the formation of clumps of spherical cells from which elongated Sertoli cells extended into the surrounding collagen to end near holes. Rhodamine-phalloidin revealed diffusely distributed actin in the spherical cells in contrast to well-developed microfilaments in the peripheral elongated cells. Addition of cytochalasin B (5 micrograms/ml) to the medium prevented contraction of the floating rafts and the development of holes in the attached collagen. In addition, cytochalasin B caused the peripheral cells to become spherical and to separate from the clumps. Moreover, rhodamine-phalloidin revealed that actin in the peripheral cells occurred as clumps without microfilaments when cytochalasin B was present. When Sertoli cells were subcultured onto silicone rubber films, the cells produced wrinkling of the rubber surface within 4 h of plating. These observations were interpreted to mean that Sertoli cells exert local tractional forces on various substrata. These forces require actin, presumably acting by a contractile mechanism. When the collagen is attached to plastic and the cells are organized into clumps with radiating elongated cells (cells from rats aged 25 d), the tractional forces in the elongated cells reorganize the collagen fibers to produce holes. When cells are uniformly distributed (cells from rats aged 15 d), holes are not formed. When the collagen is released from the plastic surface, tractional forces cause the floating rafts to shrink. These interactions of the cells with collagen are likely to be important in determining the shape of the Sertoli cell in vivo, the polarity of the cell, and its biochemical differentiation.