The signalling cascade of rods and cones use different but related protein components. Rods and cones, emerged in the common ancestor of vertebrates around 500 million years ago around when two whole genome duplications took place, named 1R and 2R. These generated a large number of additional genes that could evolve new or more specialised functions. A third event, 3R, occurred in the ancestor of teleost fish.  This thesis describes extensive phylogenetic and comparative synteny analyses of the opsins, transducin and phosphodiesterase (PDE6) of this cascade by including data from a wide selection of vertebrates. The expression of the zebrafish genes was also investigated. The results show that genes for these proteins duplicated in 1R and 2R as well as some in 3R. Expression analyses of the zebrafish genes revealed additional specialisations for the 3R gene duplicates. The transducin beta subunit genes, gnb1a and gnb1b, show co-localisation in rods but are expressed at different levels. Gnb3a and gnb3b show different expression in the adult retina with low expression of gnb3a and expression of gnb3b in cones of the dorso-medial retina. The transducin gamma subunit genes gngt2a and gngt2b are expressed in the ventral and dorso-medial retina respectively. The both of PDE6 gamma subunit genes, pde6ga and pde6gb are both expressed in rods but pde6ga shows rhythmic changes of expression with low daytime levels. Pde6ha and pde6hb are expressed in cones however pde6ha show high daytime expression. All investigated transducin and PDE6 subunit genes, but gnb1b, were also expressed in the adult pineal complex or at some point during development. These results provide compelling evidence that the 1R and 2R genome duplications facilitated the evolution of rods and cones by generating gene duplicates that could evolve distinct expression and function. This supports existence of colour vision before the origin of vertebrates, elaboration of this in the early vertebrate ancestor, along with origin of the black-and-white dim-light vision of rods. Furthermore, the different expression patterns observed in the zebrafish retina for teleost 3R duplicates demonstrate multiple additional specialisations.

Endothelial cells (EC) are essential regulator of vascular homeostasis through the generation and release of various bioactive agents, including nitric oxide (NO). NO modulates several vascular functions such as vascular tone and permeability, through the stimulation of soluble guanylate cyclase (sGC) leading to the production of cGMP. Conversely, phosphodiesterases (PDEs) are enzymes metabolizing cyclic nucleotides (cGMP and cAMP) and are therefore major regulatory players for cGMP and cAMP signalling pathways. Although ECs are the main source of NO, little is known on the endothelial NO-cGMP signalling pathway and cellular outcomes. It was then hypothesized that a specific population of cGMP-phosphodiesterases allows ECs to stabilize cGMP levels despite the elevated production of NO. Expression of cGMP-phosphodiesterases was initially studied in resistance mesenteric arteries from mice. PDE5 and PDE6 were both found at mRNA and protein levels in native arteries but PDE6 is not found in cultured ECs. Interestingly, subcellular distributions of both enzymes were distinct. PDE5 appeared to be homogeneously distributed whilst PDE6 catalytic subunits (PDE6 and PDE6) showed a preferential staining in the perinuclear region. These results suggest that PDE6 might be involved in the regulation of cGMP microdomains. Based on these findings, a mathematical model was developed. Simulations of dynamic cGMP levels in ECs support the notion of cGMP microdomains dependent on PDE6 expression and localization. In the absence of PDE6, application of NO either as a single bolus or repetitive pulses led to a homogeneous increase in cGMP levels in ECs despite PDE5 homogeneous distribution. However, PDE6 subcellular targeting to the perinuclear membrane generated a cGMP-depleted perinuclear space. The findings from this study provide the first evidence of the expression and specific intracellular distribution of PDE6 in native endothelial cells that strongly support their involvement in the generation of cGMP microdomains / Les cellules endothéliales (CEs) participent au maintien de l’homéostasie vasculaire en générant et libérant de nombreux agents bioactifs, incluant l’oxyde nitrique (NO). Le NO module plusieurs fonctions vasculaires telles que le tonus et la perméabilité vasculaire via la stimulation de la guanylate cyclase soluble (GCs) provoquant la formation de GMPc. D’autre part, les phosphodiestérases (PDEs) sont des enzymes métabolisant les nucléotides cycliques (GMPc et AMPc) et participent donc à des étapes essentielles du contrôle des voies de signalisation du GMPc et de l’AMPc. Bien que les CEs soient la source principale de NO, la voie de signalisation NO-GMPc endothéliale et les répercussions fonctionnelles demeurent méconnues. Nous avons alors émis l’hypothèse qu’une population spécifique de PDEs ciblant le GMPc (PDEs-GMPc) permettrait aux CEs de maintenir des niveaux de GMPc faible malgré l’importante production de NO. L’expression des isoformes de PDEs-GMPc dans les artères mésentériques de souris fut initialement déterminée. PDE5 et PDE6 furent détectées tant sous la forme d’ARNm que de protéines dans les artères natives alors que PDE6 est absente de lignées de CEs en culture. La distribution intracellulaire des deux enzymes est distincte. Alors que PDE5 est distribué uniformément dans le cytoplasme des cellules endothéliales, les sousunités catalytiques de PDE6 ( et ) sont préférentiellement présentes dans la région périnucléaire. Ces résultats suggèrent que PDE6 puisse être impliqué dans le contrôle de microdomaines de GMPc. Des simulations effectuées à l’aide d’un modèle mathématique développé sur la base de ces données sont en accords avec la notion selon laquelle l’expression et la distribution subcellulaire de PDE6 sont responsables de microdomaines de GMPc dans l’endothélium. En absence de PDE6, l’ajout de NO sous forme de bolus unique ou répétée mène à une augmentation homogène de la concentration cytoplasmique en GMPc malgré la présence de PDE5. Toutefois, la présence de PDE6 à la membrane péri-nucléaire crée un espace péri-nucléaire pauvre en GMPc. Les résultats de cette étude forment les premières évidences de l’expression et de la distribution intracellulaire hétérogène de PDE6 dans les cellules endothéliales natives et suggèrent leur implication dans la génération de microdomaines.