+------------SUBJ:V-N------------+                                             
      +-------COMP:N-N(of)-------+     +-------COMP:V-N(in)-------+                  
      |           +-MOD_ATT:N-ADJ+     |           +--MOD_ATT:N-N-+                  
      |           |       +MOD_AT+     |           |       +MOD_AT+                  
      |           |       |      |     |           |       |      |                  
 Expression of __SP__ __NODE__ mRNA occurs in involution stage __SP__ mammary gland .
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__)
MOD_ATT:N-N (__SP__,involution)
MOD_ATT:N-N (__SP__,stage)