Abstract
Bony fish display a skeleton that develops mainly as cartilage, locally replaced by endochondral bone tissue. Cartilaginous fish, however, have a cartilaginous skeleton, locally mineralized in various ways, some of which are evolutionary innovations specific to this lineage (prismatic cartilage, for instance). The cells associated with these tissues are thus capable of biomineralization by precipitation of calcium phosphate, a property that seems to be limited to the vertebrate clade. In this thesis, I focus on the genetics of skeletal mineralization development in a cartilaginous fish: the small-spotted catshark (Scyliorhinus canicula). I describe in detail the putative genetic factors underlying the mineralization process, and I do so through two approaches: through candidate gene studies and through transcriptomic studies. This allows me to better characterize the set of genetic mineralization tools in chondrichthyans, so that through comparative analysis, an ancestral state for jawed vertebrates can be inferred, at least partially. First, through the candidate gene approach, I test the level of conservation regarding genes known to be associated with mineralization in bony fish. Second, I describe how I used recently generated genomic and transcriptomic data in the small-spotted catshark to study intrinsic genes specifically expressed in mineralizing tissues. These two approaches allow me to detect interesting genes that are then studied through phylogenetic analyses, quantification/localization of expression in tissues, as well as comparative analyses with bony fish (when possible). In the last part, I present two papers in preparation that result from the work we have done with the help of two master students. These papers stem from a candidate gene approach but involve large gene families and in an effort to include all paralogs, the papers move towards a molecular evolutionary framework rather than an Evo-Devo framework.