Functions as a transcriptional repressor. May repress OTX2-mediated transactivation by forming a heterodimer with OTX2 on the P3C (5'-TAATCCGATTA-3') sequence. Required for brain development, neonatal survival, postnatal growth, and nursing ability. Homodimer or heterodimer. Forms heterodimers with OTX2. Expressed in adult brain, stomach, and testis. Expressed in the developing diencephalon, midbrain and hindbrain. During limb development, expressed in a temporal pattern with expression being first restricted to the forelimbs and then subsequently to the hindlimbs. Detected in embryo from 10.5 to 13.5 dpc. Strongly expressed from 9.5 to 11.5 dpc in the diencephalon, mesencephalon, metencephalon, myeloencephalon, and the developing eye. Belongs to the paired homeobox family.