First, {HEAD ~ cells} are differentiated by {TAIL ~ growing cells} in defined medium containing nerve growth factor 
are differentiated by
First , { HEAD ~ cells } are differentiated by { TAIL ~ growing cells } in defined medium containing nerve growth factor
OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH