In {TAIL ~ other embodiments} the cell or its ancestors was genetically altered with a vector to place X under control of {HEAD ~ an endogenous transcriptional control element} 
In { TAIL ~ other embodiments } the cell or its ancestors was genetically altered with a vector to place X under control of { HEAD ~ an endogenous transcriptional control element }
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD