Question

13-7 A New Wrinkle. Fibroblasts can be placed on thin sheets of
silicone rubber. Under normal circumstances, fibroblasts exert sufficient
tension on the rubber so that it visibly wrinkles. Explain how
the ability of fibroblasts to wrinkle rubber would compare with that
of normal cells under the following conditions.
(a) The cells are treated with nocodazole.
(b) The cells are treated with cytochalasin D, the drug is washed out,
and the cells are observed periodically.
(c) A constitutively activated Cdc42 is introduced into the cell.

Answer 1

Fibroblasts are cells that form and help maintain the connective tissue in animals. It plays important role in wound healing by synthesizing extracellular matrix and collagen. The connective tissue attaches to the surface by tubulin like structures or actin filaments. When these cells are placed on silicone rubber it gives rise to wrinkles because of the pressure exerted on the surface by formation of the cellular matrix.

Comparing the ability of fibroblasts to wrinkle rubber under the given conditions as compared to normal cells is explained below:

a) The cells are treated with Nocodazole

Nocodazole is a chemical agent that interferes with the polymerization of microtubules and hence it prevents a network formation by the cells, so in this condition the grip of fibroblasts on rubber will decrease and as a result less wrinkles will be observed on the surface.

b) The cells are treated with cytochalsin D, the drug is washed out, and the cells are observed periodically.

Cytochalsin D, a mycotoxin acts as inhibitor of actin polymerization, so upon its addition to cells it disrupts the cytoskletal network and as a result the number of wrinkles reduces. However, the effect of the toxin is quickly reversed once its washed off, hence after that on periodic observation the wrinkles would again reappear on surface.

c) A constitutively activated Cdc42 is introduced into the cell.

Cdc42 has a stimulating effect on microtubule dynamics. Hence, introducing a constitutively activated Cdc42 into the cell will lead to a more rigid network formation and hence cause appearance of more wrinkles on the surface.