| The vegetal cortex of the Xenopus oocyte is enriched for several mRNAs critical for early embryonic developmental processes, including germ layer specification and dorsoventral axis formation. A recent microarray screen for other vegetally localized RNAs identified several hundred novel cortex-enriched transcripts, which may have undiscovered roles in early development. In order to better elucidate the functions of localized mRNAs in early development, I characterized the spatiotemporal expression patterns and developmental functions of two novel transcripts, TRIO and F-actin binding protein ( triobp) and Cdc42 effector protein 4-like (cep4l).;Overexpression and loss-of-function experiments failed to identify a critical role for TrioBP in early Xenopus development. For Cep4l, I found that overexpression of Cep4l induced primary neuron formation throughout the epidermis, preferentially inducing primary sensory neurons. This increase came at the expense of neighboring non-neuronal ciliated and ion-secreting cells, suggesting a role for Cep4l in neural boundary formation. Additionally, I have shown that Cep4l binds specifically to Cdc42 through its known Cdc42/Rac-interactive binding (CRIB) domain, and that this activation was necessary for Cep4l function.;Morpholino (MO) oligonucleotide based inhibition of Cep4l protein synthesis resulted in decreased primary sensory neurogenesis. Additionally, I have shown that Cdc42 itself is required for sensory neurogenesis. Furthermore, I find that Fgf8a, an isoform of Fgf8 previously known to regulate neuronal development, but not the Fgf8b isoform, regulates the association of Cep4l and Cdc42. Importantly, I further show that Cep4l and Cdc42 are required for the ability of Fgf8a to induce sensory neurons.;Overall, this work suggests a novel role for Cep4l and Cdc42 in the regulation of primary sensory neuronal fate downstream of a unique Fgf8 signaling pathway. I propose that binding of Fgf8a to its receptors activates Cdc42 and recruits Cep4l, which could serve as a scaffold for integrating additional signaling pathways involved in controlling sensory neuron fate. |
