+----------COMP:V-N(in)----------+    
      +-------------SUBJ:V-N------------+              +--MOD_ATT:N-ADJ--+    
      +----COMP:N-N(of)---+             |              |         +MOD_ATT+    
      |            +MOD_AT+        +-NEG+              |         |   +MOD+    
      |            |      |        |    |              |         |   |   |    
 Expression of __NODE__ mRNA does not occur in undifferentiated 3T3 L1 cells .
COMP:N-N(of) (expression,mRNA)
MOD_ATT:N-ADJ (mRNA,__NODE__)
SUBJ:V-N (occur,expression)
NEG (occur,not)
COMP:V-N(in) (occur,cell)
MOD_ATT:N-ADJ (cell,undifferentiated)
MOD_ATT:N-ADJ (cell,3T3)
MOD_ATT:N-N (cell,L1)