NRN1 and major depressive disorder: Studies reveal that several neurotrophins, such as the brain-derived neurotrophic factor (Bdnf) mRNA [25], nerve growth factor (Ngf) mRNA [26], growth-associated protein-43 (Gap-43) mRNA [27], and neuritin 1 (Nrn1) [28], are mainly involved in the neuroplasticity regulation of depression, all of which are the downstream mRNA targets of ELAVL4.