Direct, high-resolution measurement of furrow stiffening during division of adherent cells.

It is unclear whether cell division is driven by cortical relaxation outside the equatorial region or cortical contractility within the developing furrow alone. To approach this question, a technique is required that can monitor spatially-resolved changes in cortical stiffness with good time resolution. We employed atomic force microscopy (AFM), in force-mapping mode, to track dynamic changes in the stiffness of the cortex of adherent cultured cells along a single scan-line during M phase, from metaphase to cytokinesis. Video microscopy, which we used to correlate the AFM data with mitotic events identified by light microscopy, indicated that the AFM force-mapping technique does not perturb dividing cells. Here we show that cortical stiffening occurs over the equatorial region about 160 seconds before any furrow appears, and that this stiffening markedly increases as the furrow starts. By contrast, polar relaxation of cells does not seem to be an obligatory event for cell division to occur.

Retinoic acid does not induce formation of cilia on the surface of wound epithelial cells in axolotls.

It has been reported that vitamin A palmitate induces the production of cilia on the epidermal cells of the regenerating axolotl limb, and the formation of crevices in the epidermal surface. The aim of the present investigation was to reexamine under well defined conditions the potential of retinoids to evoke the above described metaplastic changes. In order to achieve our purpose we administered axolotls with retinoic acid for 2, 4, 6, 8, and 10 days after limb amputation. The young regenerates were inspected by scanning electron microscopy (SEM). The data obtained showed that the external layer of the wound epithelium and of the stump epidermis as well was quite normal without any sign of cilia formation. In some cases, crevices were observed even in control animals.