A novel class of Pecten maximus POU gene, PmaPOU-IV: Characterization and expression in adult tissues

• We isolated the entire coding sequence of the bivalve Pecten maximus POU-IV gene.
• Sequence and phylogenetic analyses confirm that it is orthologue of POU-IV genes.
• The highest expression levels of PmaPOU-IV were found in gill and mantle (eye).
• PmaPOU-IV was moderately expressed in female gonad and parietovisceral ganglion.
• PmaPOU-IV was also expressed in male gonad and cerebropedal ganglion

POU genes encode a class of DNA-binding proteins that interact with DNA through a bipartite domain of ~ 150 amino acids. This domain is composed of two highly conserved regions, an N-terminal POU specific domain and a C-terminal POU homeodomain, separated by a non-conserved linker. POU domain proteins are currently grouped into six or seven classes. In a variety of organisms, including Drosophila, Caenorhabditis and vertebrates, POU proteins have been shown to play critical roles in the development and functioning of the nervous and neuroendocrine systems. POU-IV class genes regulate neuronal metazoan development, including a range of sensory neurons. However in Lophotrochozoa, their presence, function and expression is not well studied, especially in the phylum Mollusca.In this study, we have isolated and fully sequenced a homologue of the vertebrate Brn-3 gene from the bivalve mollusc Pecten maximus (L.), which we have called PmaPOU-IV. The derived amino acid sequence exhibits characteristic features of POU-IV proteins. First, the new sequence includes a POU-specific domain and a POU-homeodomain. Second, PmaPOU-IV contains a POU-IV box, found only in the proteins of class IV. Third, the Pecten POU-IV bipartite domain shares a significant amino acid sequence identity with other members of the POU-IV class. Finally, phylogenetic analyses confirm that PmaPOU-IV is an orthologue of POU-IV genes. We have also investigated by reverse transcription quantitative real time PCR (RT-qPCR) the expression pattern of PmaPOU-IV in adult tissues. PmaPOU-IV was expressed in several sensory organs and gonads but was undetectable in both muscle and the digestive gland. Our findings support the belief that POU class IV genes involved in the terminal neuronal differentiation are still operating in the adult nervous system.

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