Transcription factor that binds specifically to the DRE (dual repressor element) and represses 5-HT1A gene transcription though this element. Mediates HDAC-independent repression of HTR1A promoter. CAMK2G inhibits CC2D1a-induced repression of the HTR1A. May play a role in the altered regulation of 5-HT1A receptors associated with anxiety and major depression. Performs essential function in controlling functional maturation of synapses (By similarity). Strongly expressed in several brain areas including frontal cortex, cortex, mesencephalon, hippocampus, midbrain and hypothalamus. Also expressed in testis and at low levels in pituitary, liver and kidney. In brain the highest levels are detected in hippocampal pyramidal cells and raphe nuclei. The C2 domain is required for the repression. Belongs to the CC2D1 family.