ABSTRACT
Normal mammalian embiyo cells in culture exhibit a series of growth properties which apparently distinguish them from cells of established lines. Analysis of the process of immortalization definitely relies on the predictable growth pattern of the indicator cells, usually primary embryonic rodent cells. However, these experiments are often complicated by unforeseen variations in their growth behavior in culture. Sometimes, cells escape from growth restriction at low cell density, sometimes they grow for several number of generations without entering cell crisis, and sometimes they segregate established derivatives with unexpected high frequencies. Most of the relevant experiments on oncogene-mediated two-step transformation of rodent cells have been performed with cells from embryos explanted between gd 12 and 14 without paying particular attention to precise aging. Since a manuscript with a detailed analysis of intrinsic distinct growth properties of differently aged rat embryos is currently submitted, it appeared expedient to present briefly the relevant experimental basis.
