Analysis by computer-controlled cell sorter of Friend virus-transformed cells in different stages of differentiation.

In most systems involving cellular differentiation and cellular transformation the biological process is non-synchronous and the sample heterogeneous. In order to answer some of the basic questions about the control mechanisms of cellular changes and the order in which they proceed one must have access to homogeneous classes of cells. Friend virus transformed erythroid cells which are stably maintained in tissue culture can be chemically induced to differentiate and are thus very advantageous for in vitro studies (1-3). With such a system the questions which we pose are a) the reversibility of the differentiation process; b) the order of steps in the production of specialized messenger RNA; c) the time of shut-off of undifferentiated messenger production; d) the relationship of viral RNA production to the differentiation process; e) the onset and extent of specific protein synthesis; f) the correlation of DNA metabolism with the timing or course of events. By using a computer-controlled cell separator we can select live cells on the basis of their macromolecular content, membrane properties (using a new parameter, fluorescence emission anisotropy), and size (4, 5, 34). Thus with proper probes as described here, we are able to select cells at different stages in their differentiation and can begin to attack the questions posed above.