Involved in the differentiation of bipolar cells, the last neurons of the retina to form. Together with other retinal homeobox proteins, acts as an effector of a cellular clock which, depending on cell cycle progression, establishes the generation of distinct retinal neuronal cell types. Initially transcribed but not translated in early neural (stage 15) retinal progenitors. Translation occurs during late retinogenesis and requires cell cycle progression with the timing of translation paralleling that of the generation of bipolar cells. Also expressed in the ciliary marginal zone (CMZ) with translation beginning in early postmitotic cells. Also transcribed in early neurulae in the presumptive spinal cord, with expression expanding anteriorly to the midbrain-hindbrain boundary during the tail bud stage. First transcribed in the neurula at stage 15 and is maintained throughout later stages, reaching a peak around stage 42. Belongs to the paired homeobox family.