Transcription factor involved in developmental processes such as cell fate determination, gene transcriptional regulation and progenitor cell regulation in a number of organs. Plays a critical role in embryonic development and functions as a key regulatory protein in neurogenesis and the development of the heart, eye lens, liver, pancreas and the lymphatic system. Involved in the regulation of the circadian rhythm. Represses: transcription of the retinoid-related orphan receptor RORG, transcriptional activator activity of RORA and RORG and the expression of RORA/G-target genes including core clock components: ARNTL/BMAL1, NPAS2 and CRY1 and metabolic genes: AVPR1A and ELOVL3. Interacts with RORA and RORG (via AF-2 motif). RORG promotes its nuclear localization. Most actively expressed in the developing lens. Detected also in embryonic brain, lung, liver and kidney. In adult, it is more abundant in heart and liver than in brain, skeletal muscle, kidney and pancreas. The Prospero-type homeodomain and the adjacent Prospero domain act as a single structural unit, the Homeo-Prospero domain. The Prospero-type homeodomain is essential for repression of RORG transcriptional activator activity. Belongs to the Prospero homeodomain family.