The cells contain {TAIL ~ an effector gene} under control of a transcriptional control element that causes {HEAD ~ the gene} to be expressed in relatively undifferentiated cells in the population 
The cells contain { TAIL ~ an effector gene } under control of a transcriptional control element that causes { HEAD ~ the gene } to be expressed in relatively undifferentiated cells in the population
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH