Annona, Giovanni (2015) Study of evolution, expression and function of Nitric Oxide Synthases in the cephalochordate Branchiostoma lanceolatum. [Tesi di dottorato]

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Nitric oxide (NO) is a highly reactive, diffusible gas, essential for many physiological functions including neurotransmission, learning and memory, cardiovascular homeostasis, angiogenesis, host defense through immune response, cell migration, and apoptosis. In vertebrates, NO is produced by the enzymatic conversion of L-arginine by three distinct Nitric Oxide Synthase (NOS) that have been identified as products of different genes with distinct expression patterns, cellular localization, regulation, catalytic properties and inhibitor sensitivity. The pathway of NO formation is one of the oldest bioregulatory systems, highly conserved in metazoan. Comparative studies in different model systems using non-vertebrate organisms, especially basal chordates, are very useful. Because it is likely that the basic primary roles will be evolutionary conserved, the chordate amphioxus is the best available stand-in for the ancestor of the vertebrates. Importantly, amphioxus has a body plan, central nervous system, circulatory system and genome that are vertebrate-like, but simpler. In addition, in comparison to vertebrates, amphioxus has the same spectrum of gene families, but has markedly fewer genes per family (Holland et al., 2008; Putnam et al., 2008). This relative genomic simplicity makes amphioxus an especially favorable prospect for functional studies of signaling networks and other physiological processes. Amphioxus has 3 NOS genes although evolutionary analysis has shown that there is no a direct relationship between the 3 amphioxus NOS and vertebrate eNOS, nNOS and iNOS genes (Andreakis et al., 2011). This indicates that, despite its high conservation, NOS evolution has also been very dynamic in some respects, with recurrent episodes of lineage-specific gene duplications. The study of amphioxus NOS will help to understand the acquisition of new functions of NOS enzymes, but also might illustrate convergent evolution events during NOS evolution. The following thesis project is designed to accomplish the first complete and detailed study of NOS during development. Although much has been published on NOS expression and function in many different organisms, very little is known about its role during the first stages of animal development.

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