Cytosolic NPAS4 interacts with both isoforms of MAGED1 (Melanoma-associated antigen D1), MAGED1-1 (also known as MAGED1b) and MAGED1-2 (also known as MAGED1a). Besides NPAS4, MAGED1 interacts with several other basic helix-loop-helix (bHLH) PER-ARNT-SIM (PAS) family proteins, including NPAS4 heterodimerization partner ARNT2. The interaction with MAGED1 involves the PAS repeat domain, which is also the interface for bHLH PAS heterodimerization. Therefore, MAGED1 does not interact with NPAS4 heterodimers. MAGED1 does not affect protein levels of NPAS4, but is thought increase its transcriptional activity by enhancing its function prior to nuclear import (Sullivan et al. 2016). Maged1 knockout mice show decreased levels of Bdnf and impaired memory formation (Yang et al. 2015), showing at least a partial phenotypic overlap with Npas4 knockout mice (Lin et al. 2008, Ramamoorthi et al. 2011).