The Wnt gene family in evolution and development: insights from Chilopoda
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The importance of a relatively small number of highly conserved genes and signalling systems, which can be co-opted to many developmental functions over evolutionary time, is a central finding in the field of evolutionary developmental biology. As the genes of the Wnt family are prominent members of this ¿genetic toolkit¿, the study of how these genes operate in various taxa has the potential to yield useful insights into how development and evolution interact. This thesis tackles such issues by examining the development of centipedes, focusing on the developmental roles played by Wnt genes. First, a comparative study of limb development, segmentation and Wnt1 expression in three chilopod species was performed. Second, an analysis of Wnt expression in the forcipular segment of Strigamia maritima, a unique feature and an interesting case study for evolution in body patterning, was performed. Third, the roles of Wnt genes in the linked developmental processes of posterior development and segmentation in Strigamia maritima were investigated. This analysis included both detailed expression studies and newly-developed functional techniques based on chemical perturbation of the Wnt signalling system. Fourth, a census of Wnt genes present in Strigamia maritima and thorough analyses of their expression were performed, paying particular attention to the combinatorial action of these genes. Several interesting findings have resulted from this study, including the conservation of posterior development functions in Strigamia, the presence of non-canonical segment boundary formation in centipedes and the involvement of Wnt genes in many developmental functions, constituting a mosaic of conserved and novel ones.