Molecular and evolutionary analysis of the development of the nervous and visual systems of the cuttlefish Sepia officinalis (Cephalopoda) : dopaminergic and photosensitive receptors

Cephalopods, especially Sepia officinalis, have been extensively studied for their visually guided behaviour and their cognitive abilities that set-up during embryogenesis. The aim of this PhD thesis was to identify and characterize both dopaminergic and photosensitive receptors (opsins and cryptochromes) involved in learning and memory formation in order to better understand their molecular function and evolution in the cuttlefish. In the first study, three families of dopaminergic receptors were phylogenetically identified in S. officinalis. This identification was functionally confirmed for two of these families. All of these receptors are expressed starting from embryogenesis in the eyes and the nervous cognitive centers (e.g. the brain and optic lobes). An investigation of photosensitive receptors identified: three opsins (one r-opsin and two retinochromes), a cryptochrome and a visual arrestin that all seem specifically expressed in the eyes of the cuttlefish embryo during the early development of the visual system. Some of these genes are also expressed in other tissues with photosensitive properties (e.g. the brain, optic lobes and skin). Putative actors in the phototransduction cascade were also found to be expressed in the eyes. Finally, a study of the « Clock system » and the influence of photoperiod on this system and on the photosensitive receptors was initiated. This study serves to better characterize the diversity of molecular actors in the nervous and visual system of S. officinalis. Data about the expression of these actors in various tissues and at different steps of the cuttlefish life cycle were generated. This work paves the way for studying comparative physiology and the influence of environmental cues on the setting up of the nervous and visual systems.