Transcriptional repressor that may play a role in the specification and differentiation of lung epithelium. May also play a role in developing neural, gastrointestinal and cardiovascular tissues. Can act with CTBP1 to synergistically repress transcription but CTPBP1 is not essential. Plays a role in synapse formation by regulating SRPX2 levels. Forms homodimers and heterodimers with FOXP1 and FOXP4. Dimerization is required for DNA-binding (By similarity). Interacts with CTBP1 (PubMed:14701752). Interacts with FOXP1 (By similarity). Interacts with TBR1 (By similarity). Interacts with ZMYM2 (By similarity). Highest expression in lung. Lower expression in spleen, skeletal muscle, brain, kidney and small intestine. Expressed in developing lung, neural, intestinal and cardiovascular tissues. Expressed at a high level in the distal airway epithelium and at a low level in the proximal airway epithelium at 12.5 dpc, and restricted to the distal airway epithelium by 14.5 dpc. In the spinal cord, at 12.5 dpc, expressed in a subset of interneurons dorsal to motor neurons. At 16.5 dpc, expression in the brain is observed in the inner intermediate zone of the neopallial cortex and in the developing cerebral hemispheres. In the gastrointestinal system, at 12.5 expressed in the outer mesodermal layer and in the intestinal epithelium. By 16.5 dpc, expression is restricted to the outer longitudinal muscle layer of the intestine and stomach. In the cardiovascular system, at 14.5 dpc, expressed in the outflow tract region of the developing heart. By 16.5 dpc, observed in the outflow tract and atrium, but not in the ventricles. The leucine-zipper is required for dimerization and transcriptional repression. May be due to a competing acceptor splice site.