| Otx1 and Otx2 are closely related homeodomain transcription factors of the orthodenticle family that act as central regulators of anterior neural patterning, forebrain–midbrain regionalization, and sensory organ development, and they function in a partially dosage‑dependent and overlapping manner to control morphogenesis of rostral central nervous system territories. The proteins share a conserved homeodomain that binds TAAT‑containing DNA motifs and flanking regulatory regions that confer distinct temporal and spatial expression, with Otx2 expressed earlier in epiblast and visceral endoderm and then throughout anterior neuroectoderm and cephalic mesenchyme, and Otx1 expression initiating slightly later in anterior neuroectoderm and contributing to cortex and sense organ development. Otx2 establishes and maintains anterior neural plate identity and is required for induction and stabilization of forebrain–midbrain neuroectoderm, positioning the midbrain–hindbrain boundary and isthmic organizer and cooperating with FGF8 and other patterning signals to define mesencephalic and diencephalic territories, while Otx1 acts with Otx2 in a gene dosage‑dependent network that refines mes/diencephalic patterning and supports corticogenesis, including cortical thickness and neuron number. These factors also participate in eye patterning, where combined Otx1/Otx2 dosage is required for specification and differentiation of the retinal pigment epithelium, proper optic vesicle folding, and restriction of neural retina and optic stalk domains, and reduced Otx gene dosage produces profound ocular malformations with loss of pigment epithelium markers, expansion of neural retina territory, and abnormal proliferation and differentiation within the retina. Otx1 can substitute for most Otx2 functions when expressed under Otx2 regulatory control, supporting a high degree of functional equivalence in many contexts, but Otx2 retains unique functions in the earliest anterior neuroectoderm before Otx1 onset, and complete loss of Otx2 eliminates structures anterior to rhombomere 3, whereas Otx1 loss preferentially affects telencephalic cortex and sensory systems and is associated with epilepsy and neuroendocrine and sensory defects. In later development and adult tissues, Otx1 and Otx2 expression persists in selected neuronal populations, including sensory and autonomic circuits such as myenteric neurons, where they influence neuronal phenotype and may contribute to plasticity and disease‑related remodeling of enteric and central neural networks. |
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