A rare family tree of cultured rat cells showing a change in proliferative potential

In most family trees examined by time-lapse cinemicrography of proliferative rat liver epithelial-like cells in primary culture, a clonal population first expanded, and then ceased to expand. We encountered one rare family tree in which a clonal population first expanded, stopped expanding for a while, and then began to expand again. In this family tree, we noted one particular intermitotic cell, all descendants of which divided during the period of observation when the rest of the cells had ceased division. We consider that this rare family tree showed for the first time part of the process of indefinite proliferation.