The multipotent cells comprising the vertebrate neural crest (NC) generate an astonishing array of derivatives, including neuronal, skeletal and adrenal components and pigment cells. Zebrafish possess three chromatophores lineages, melanophores, iridophores and xanthophores, which lend themselves to investigating the complex gene regulatory networks (GRNs) underlying fate segregation of NC progenitors. Although the core GRN governing melanophore specification has been previously established, those guiding iridophore and xanthophore development remain elusive.This study explores the iridophore specification GRN via a previously employed systems biology approach. Loss and gain of function experiments were used to derive a preliminary GRN (model A), mathematically modelled using a system of differential equations and computationally simulated to predict gene expression dynamics. Predictions were experimentally evaluated and testable hypotheses were derived to render simulations of the resulting model B consistent with experimental observations. Iterations of this process led to a more sophisticated model D, which accurately predicted observed expression dynamics.Firstly, mutant phenotypes identified the transcription factors Sox10, Tfec and Mitfa and the receptor tyrosine kinase, Ltk, as key players for model A. Regulatory interactions were derived by analysing the spatiotemporal gene expression patterns on wild-type and mutant embryos by in situ hybridisation. Data indicated a sox10-dependent tfec/ltk positive feedback loop driving iridophore specification. Cycles of mathematical modelling and experimentation revealed important regulatory features, such as sox10 maintenance throughout iridophore development and its cooperation with tfec to activate the differentiation gene, pnp4a. Candidate repressors of mitfa, a melanocyte-specific target of sox10, were investigated. Surprisingly, data presented challenge the reported role of Foxd3, an established mitfa repressor, in iridophores.This study established the core GRN guiding specification of the NC-derived iridophore lineage using systems biology. Presented results reveal previously unacknowledged molecular mechanisms underlying fate choice and demonstrate the value of integrating experimental and mathematical approaches when investigating GRNs.
|Date of Award||27 Jun 2017|
|Sponsors||Biotechnology and Biological Sciences Research Council|
|Supervisor||Robert Kelsh (Supervisor) & Hartmut Schwetlick (Supervisor)|