A New Twist on an Animal Model Reveals Environmental Constraints on Selection

Human Platt neuroblastoma cells were transfected with the marker gene, bacterial lacZ, to track cells at the earliest stages after ectopic injection at two different sites in athymic nude mice. Three clones (LZPt-1,-2 and -3) of differing morphologies were analysed. All clones yielded large primary tumours subcutaneously or intradermally with similar latency. While LZPt-2 and -3 clones generated well-staining primary tumours, LZPt-l cells yielded many non-staining tumours, indicating greater instability of lacZ expression for this clone in situ (stability of lacZ expression in culture was similar for all three clones). After