Biology

Gareth Fraser: Postdoctoral Fellow

Current Research

My diverse background led me through the disciplines of palaeobiology and evolutionary biology, before heading on to my current research path of evolutionary developmental biology (EvoDevo). This affair began during my Ph.D at King’s College London, where I employed the use of the rainbow trout (Oncorhynchus mykiss), a mighty fine teleost model, ideal for investigations focusing on the evolution and development of vertebrate dentitions. I was able to make comparisons between trout tooth development and previously known murine odontogenic regulation. This involved the detailed study of the key genes implicated in both the early patterning and continued production of the teleost dentition. From these studies on the rainbow trout it was clear that many genes are similarly utilized across vertebrates, from fish to mammals, for the production of a common structure, the tooth and the patterning of a complete dentition; a conservation spanning more than 420 million years. Teleost models surpass the classical murine developmental model for odontogenesis, as teleosts have a continuous production of replacement tooth generations (polyphyodontism), whereas the mouse has a single generation of teeth (atypical, even among mammals!).

The trout has the advantage over other popular teleost developmental models, such as the zebrafish (Danio rerio), due to the extensive distribution of teeth throughout the oro-pharynx, with teeth occupying territories on the premaxilla, maxilla, dentary, basihyal (pseudo-tongue), palate, vomer, and posterior epibranchials and ceratobrachials (with also a number of tooth-like structures lining the surface of gill rakers). This facilitated the preliminary study into whether the development of teeth located on the oral jaws are governed by the same genetic factors as those teeth that form in posterior pharyngeal regions, a tooth bearing location that can be traced back to extinct agnathan fish (prior to the evolution of jaws). Interestingly, a number of differences in the expression of certain genes are observed between the oral and pharyngeal dentition.

Currently, in the Streelman Lab I am interested in the developmental genetic basis of morphological diversity in Malawi cichlid fish and this diversity is seen nowhere better than that reflected by the dentition across species. What are the factors that produce diverse phenotypes in closely related species? Can we observe differences in the deployment of key odontogenic regulatory genes that might lead to the production of the range of dental phenotypes in Malawi cichlids? What alterations occur in the regulation of the odontogenic network that facilitates change, not only in tooth shape, but also in tooth replacement patterns and tooth row numbers? The diversity of cichlid oral tooth shape and number is extreme, with examples of unicuspid, bicuspid and tricupid teeth, from one row of teeth to 15 or more (separate rows each tooth continuously replaced). As is the case with many teleost fish, cichlids possess two sets of functional jaws for the breakdown of food.  In the Streelman Lab I will also be continuing my investigation into the molecular specifications of the oral versus pharyngeal jaws and the dentitions which these jaws house. I will investigate the fundamental developmental conservation between the two units and isolate potential differences that might be a reflection of environmental disparity, for example the oral jaws develop in a Hox - negative environment, whereas the region at the posterior pharynx where the pharyngeal jaw and dentition develop is Hox - positive.

Publications

2006 Fraser, G.J., A. Graham and M.M. Smith. Developmental and evolutionary origins of the vertebrate dentition: molecular controls for spatio-temporal organisation of tooth sites in osteichthyans. JEZb:MDE DOI 10.1002/jez.b21097. (PDF)

2004 Fraser, G.J., A. Graham and M.M. Smith. Conserved deployment of genes during odontogenesis across osteichthyans. PRS 271: 2311-2317. (PDF)