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