Transcriptional regulator involved in pattern formation and cell determination in the embryonic CNS and larval imaginal disks. Also later in development to coordinate the expression of regulatory and structural genes required for photoreceptor cell fate in the ocelli. Has a dual role in the terminal differentiation of subtypes of photoreceptors by regulating rhodopsin (rh) expression: essential for establishing the expression of rh genes in the pale subset of ommatidia as well as repressing Rh6 in outer photoreceptors. Expressed in the anterior region of the embryo before cellularization and becomes localized to the procephalic head region following gastrulation. These cells correspond to the mesectoderm or midline neuroepithelium and will generate a mixed population of neurons and glia. Expressed in photoreceptors in pupae and adults. Expressed from early embryonic stages through to late pupation. Contains multiple repeats consisting of single amino acids (e.g. Gly, Ser, His, and Asn) and pairs of amino acids (e.g. Gly-Val). In embryos, formation of an abnormal neuropil and the disappearance of the horizontal commissures associated with the midline of the CNS. In pupae, misshapen, duplicated, and shortened rhabdomeres within the eye. In adults, deletion of the ocelli. Belongs to the paired homeobox family.