"Contact inhibition" of alpha-fetoprotein synthesis and junctional communication in adult mouse hepatocyte culture.

Synthesis of oncofetal serum protein alpha-fetoprotein (AFP) may be reexpressed in adult differentiated mouse hepatocytes both in regenerating liver and in primary monolayer culture of intact adult liver. We have found that appearance of AFP in these cultures was strongly correlated with the loss of junctional communication between hepatocytes as tested by the dye transfer method. When in hepatocyte culture the gradient of cell density was formed, and the cells in the center of the dense monolayer retained an epithelial morphology and junctional communication and were AFP-negative during 5 days of culture. At the periphery of the monolayer hepatocytes lost junctional communication by the third day of cultivation. They acquired fibroblast-like morphology, formed multilayered sheets, and started to produce AFP. These findings suggest that reexpression of AFP synthesis may be regulated through a process related to "contact inhibition" and junctional communication might play an important role in the phenomenon.

Induction of intercellular communications in epithelial cell cultures.

A popular criterion of cell-cell communication in tissue cultures is dye coupling: the ability of the injected fluorescent dye of low molecular weight to be transferred from one cell to another. We report about a new factor which induces cell-to-cell dye coupling in previously uncoupled epithelial sheets. Paradoxically it is the standard fluorescent microscopy itself (that is, blue light of 320- to 480-nm wavelength) which induces rapid morphological alterations of cell culture followed by the transfer of fluorescent dye from one cell to another. Thus monitoring cell-cell dye coupling by fluorescent microscopy may itself induce the dye coupling in previously uncoupled epithelial cells.