An investigation into the critical domains and function of XMI-ER1 during xenopus development

The FGF signal transduction pathway has been linked to many events that occur throughout vertebrate development. Model systems, such as the amphibian Xenopus laevis, have been used to define numerous components of this signalling cascade. One such discovery was Xmi-er1, a maternally derived immediate-early gene in the FGF pathway thought to act in transcriptional regulation. The purpose of this project was to further characterize the activity of XMI-ER1 in the developing Xenopus embryo and to explore how this activity relates to its molecular structure. -- Over-expression of Xmi-er1 resulted in truncations along the anteroposterior axis. These abnormalities first become apparent during gastrulation. Analysis of tissue development using antibodies demonstrated that both mesodermal and neural tissues are affected by Xmi-er1 over-expression, yet differentiation still occurs in the most severe cases. In FGF-induced mesoderm induction, this event was partially inhibited in the presence of excess XMI-ER1. No analogous inhibition was observed with mesoderm induction by activin. Also suppressed was part of the expression pattern of the early mesodermal marker, brachyury. Subsequent examination of the various domains present in the protein implicated a proline-rich region in the over-expression activities of XMI-ER1 throughout development, however the investigation failed to connect both the SANT domain and the ELM2 domain to this effect. Overall, these results indicate that XMI-ER1 functions in some FGF-related cellular activities, such as mesoderm induction, but that its role may not be limited to this pathway. This function appears to be dependent upon the proline-rich region