With regard to the differential regulatory mechanism (s) underlying MDD, six key-DRGMDD (FOSL1, SRF, JUN, TFAP4, SOX9, and HLF) and 16 key-DRLMDD (TF2target DCLs) appear to be the key differential factors in MDD (Table 2). Here, TFAP4 is linked to major depressive disorder.