Tissue-specific DNA-binding transcription factor involved in the development and differentiation of target cells. Functions either as activator or repressor modulating the rate of target gene transcription through RNA polymerase II enzyme in a promoter-dependent manner. Binds to the consensus octamer motif 5'-AT[A/T]A[T/A]T[A/T]A-3' of promoter of target genes. Plays a fundamental role in the gene regulatory network essential for retinal ganglion cell (RGC) differentiation. Binds to an octamer site to form a ternary complex with ISL1; cooperates positively with ISL1 and ISL2 to potentiate transcriptional activation of RGC target genes being involved in RGC fate commitment in the developing retina and RGC axon formation and pathfinding. Inhibits DLX1 and DLX2 transcriptional activities preventing DLX1- and DLX2-mediated ability to promote amacrine cell fate specification. In cooperation with TP53 potentiates transcriptional activation of BAX promoter activity increasing neuronal cell apoptosis. Negatively regulates BAX promoter activity in the absence of TP53. Acts as a transcriptional coactivator via its interaction with the transcription factor ESR1 by enhancing its effect on estrogen response element (ERE)-containing promoter. Antagonizes the transcriptional stimulatory activity of POU4F1 by preventing its binding to an octamer motif. Involved in TNFSF11-mediated terminal osteoclast differentiation. Interacts with POU4F1; this interaction inhibits both POU4F1 DNA-binding and transcriptional activities. Interacts (C-terminus) with ESR1 (via DNA-binding domain); this interaction increases the estrogen receptor ESR1 transcriptional activity in a DNA- and ligand 17-beta-estradiol-independent manner. Interacts (via C-terminus) with TP53 (via N-terminus). Interacts with DLX1 (via homeobox DNA-binding domain); this interaction suppresses DLX1-mediated transcriptional activity in postnatal retina enhancing retinal ganglion cell (RGC) differentiation. Interacts with DLX2 (via homeobox DNA-binding domain); this interaction enhances RGC differentiation. Interacts (via C-terminus) with ISL1 (via C-terminus). Interacts with ISL2. Interacts with LHX2. Expressed in the heart, brain and spinal cord (PubMed:8835784, PubMed:18368538). Expressed in cardiomyocytes (at protein level) (PubMed:18368538). Expressed in brain and spinal cord (PubMed:8835784, PubMed:18368538). Expressed in dorsal root ganglion (RGD) neurons (PubMed:8835784). The N-terminal transcriptional activation region is sufficient to induce transcriptional activity. The POU-specific domain and POU homeodomain regions are necessary for DNA-binding activity and transcriptional repression. The polyhistidine motif acts as a targeting signal to nuclear speckles. Belongs to the POU transcription factor family. Class-4 subfamily.