Polarization of cytoplasmic fragments microsurgically detached from mouse fibroblasts

We have studied the polarity of cytoplasm organization in tiny fragments of mouse embryo fibroblasts, produced by the microsurgical separation of long processes of cytochalasin-treated cells. In the cytochalasin-free medium fragments respread and developed small lamellas at one or both of their ends. Granules, visible at phase-contrast optics, were always collected in the central part of the fragment. Lamellas of the fragment, as well as lamellar cytoplasm of parent cells, were able to clear surface receptors patched by concanavalin A and an antibody to concanavalin A. Immunofluorescence microscopy showed that the fragments always contained actin microfilament bundles parallel to the long axis of the fragment, but microtubules were present not more than for 6 hrs after detachment of the fragments from the cell bodies. Fragments detached from the cells treated with colcemid and cytochalasin simultaneously and transferred into the drug-free medium never had any microtubules. In spite of that, their behaviour was similar to the behaviour of the fragments that were produced from the control cells treated only with cytochalasin. These results show that the small fragments of mouse embryo fibroblasts are able to maintain the polar organization of cytoplasm and the microtubules are not responsible for this organization.