| Summary: | The sea urchin apical organ constitutes a fundamental part of the larval nervous system and forms a neuro-sensory structure capable of sensing environmental cues and coordinating swimming behaviour. However, the gene regulatory network (GRN) that underlies the specification of this structure is poorly understood. The first step in building an apical organ GRN, is the high-resolution characterisation of regulatory genes in both time and space. This information then allows the regulatory states of the apical domain to be determined and identifies the existence of different spatial domains. In this study, spatial and temporal expression data of regulatory genes were overlaid onto cellular maps of the apical domain at different developmental stages. These cellular maps were then used to establish the different regulatory states that occur in the apical domain and their dynamics during development. This analysis illustrated that the spatial organisation of the apical domain is far more complex and dynamic than previously thought. The rest of the thesis focuses on functional analysis, and addresses the role of FGF signalling in the development of the apical organ. Embryos injected with a fgfr1 morpholino or incubated with SU5402, a common chemical inhibitor of FGFR1, show an upregulation in a limited group of apical organ genes. Surprisingly, the two methods of disrupting FGFR1 did not affect similar genes, and suggests that an unspecific perturbation is occurring. Functional analysis was also carried out on zic2, an apical organ transcription factor upregulated by SU5402 treatment. The results show that zic2 represses itself and is required for a normal complement of serotonergic neurons.
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