Expression of AmphiPOU-IV in the developing neural tube and epidermal sensory neural precursors in amphioxus supports a conserved role of class IV POU genes in the sensory cells development

POU genes play a prominent role in the nervous system differentiation of several organism models, and in particular, they are involved in the differentiation of sensory neurons in numerous invertebrate and vertebrate species. In the present report, cloning and expression profile of a class IV POU gene in amphioxus was assessed for understanding its role in the sensory systems development. A single class IV gene, AmphiPOU-IV was isolated from the amphioxus Branchiostoma floridae. From a phylogenetic point of view, AmphiPOU-IV appears to be strictly related to the vertebrate one, sharing a high homology ratio especially with all vertebrate POU-IV proteins Brn-3a, Brn-3b, and Brn-3c. AmphiPOU-IV was found in the most anterior neural plate and in scattered ectodermic cells on the flanks of neurula, such ectodermic cells resemble the characteristic morphology and position of AmphiCoe and AmphiTrk developing sensory cells. Later on, the expression was confined in some motoneurons at level of the PMC and in some segmental arranged motoneurons in the hindbrain. Such expression is also maintained in larvae, and a new site of AmphiPOU-IV expression was also found in rostrum and mouth edge epidermal sensory cells of the larva. In conclusion, our data suggest an evolutionary conserved role of POU-IV transcription factors in the specification and differentiation of the sensory system in both vertebrates and invertebrates and underline the importance of amphioxus as linking step between them.