+-------------------SUBJ:V-N------------------+    
      +--------COMP:N-N(of)-------+                 |    
      |            +-MOD_ATT:N-ADJ+                 |    
      |            |      +MOD_ATT+                 |    
      |            |      |       |                 |    
 Expression of __NODE__ mRNA [__NODE__] in brain occurs .
COMP:N-N(of) (expression,[__NODE__])
MOD_ATT:N-ADJ ([__NODE__],__NODE__)
MOD_ATT:N-N ([__NODE__],mRNA)
SUBJ:V-N (occur,expression)