Transcription factor required for the formation of correct projections from nociceptive sensory neurons to the dorsal horn of the spinal cord and normal perception of pain. Interacts with RGMB. Expressed in most sensory neurons but not in autonomic neurons. Also expressed in the dorsal horn of the spinal cord. First detected at E12.5 in the nervous system and in the dorsal root ganglia of the trunk region. By E15.5, strong expression in trunk and dorsal spinal cord and at E17.5 expression increases in the dorsal horns. Belongs to the paired homeobox family.