Mechanochemical proteins, cell motility and cell-cell contacts: the localization of mechanochemical proteins inside cultured cells at the edge of an in vitro "wound".

We have examined the distribution of several mechanochemical proteins inside rat A10 cells in monolayer culture, both in sparse cultures and at the edges of in vitro "wounds" in confluent cultures. The proteins examined were actin, myosin, tropomyosin, alpha-actinin, filamin, and tubulin. In each experiment, a pair of these proteins (one of which was usually actin) were examined simultaneously by double fluorescence staining methods. Actin was specificially stained by double fluorescence staining methods. Actin was specifically stained by a method based on heavy meromyosin binding, while the other proteins were specifically stained by indirect immunofluorescence procedures. The most important of the various results described was obtained with cells moving out from the edge of an in vitro wound. Within the flat leading lamella of such a cell, there was an extended region in which myosin was severely depleted or absent compared to the proximal regions of the same cells. By contrast, the other proteins were abundantly present throughout the leading lamella, except for tropomyosin, which was somewhat depleted but not as extensively as myosin. In Nomarski optics, there was no detectable morphological differentiation between the region depleted of myosin and the more proximal portion of the same lamella. While the depletion of myosin from the motile regions of cells does not rule out the involvement of some form of an actomyosin sliding filament mechanism, it suggests that other molecular mechanisms for generating motility be seriously considered.