+------------SUBJ:V-N------------+                    
      +-------COMP:N-N(of)-------+     |                    
      |           +-MOD_ATT:N-ADJ+     |                    
      |           |       +MOD_AT+     +COMP:V-N(+          
      |           |       |      |     |         |          
 Expression of __SP__ __NODE__ mRNA occurs in __SP__ penis .
COMP:N-N(of) (expression,mRNA)
MOD_ATT:N-ADJ (mRNA,__SP__)
MOD_ATT:N-ADJ (mRNA,__NODE__)
SUBJ:V-N (occur,expression)
COMP:V-N(in) (occur,__SP__)