Project Summary/Abstract Zika virus was responsible for the 2015 outbreak of microcephaly in Brazil. A concerted worldwide research effort began to study Zika virus and its impacts on fetal neurodevelopment. These initial studies discovered that Zika virus was capable of infecting neural progenitor cells, leading to the disruption of proliferation and differentiation of these cells. However, the molecular mechanisms underlying the disease caused by Zika virus have yet to be elucidated. The Ott lab recently described the interaction of Zika virus with the Non-sense Mediated Decay pathway, an RNA surveillance pathway responsible for destroying aberrant mRNAs, in neural progenitor cells. However, this pathway also plays an important role in cellular homeostasis and neurodevelopment due to the its ability to regulate a significant portion of the transcriptome. In this first study, the Ott lab found that Zika virus induced disruption of the NMD pathway. Interactions between the viral capsid protein and Upframeshift Protein 1 (UPF1), the master regulator of the Nonsense Mediated Decay pathway, was defined and showed this interaction led to the nuclear degradation of UPF1. Lastly, UPF1 was shown to be a viral restriction factor and knockdown of this factor enhanced permissivity of neural progenitor cells to infection. The initial study set the groundwork for future studies, but many open questions remain. I propose to study the mechanism by which UPF1 is degraded during infection and what are the downstream consequences of Nonsense Mediated Decay disruption in neural progenitor cells. Preliminary data shows that UPF1 degradation by ZIKV capsid can be rescued by proteasomal inhibition. Furthermore, we also know that 96 previously defined UPF1 targets are upregulated during infection. Therefore, in Aim 1 I propose to study UPF1 degradation during infection of neural progenitor cells to better elucidate the mechanism by which Zika virus inhibits UPF1 function. In Aim 2, I will describe the downstream impacts that the aforementioned UPF1 disruption has on neural progenitor cell capabilities, including proliferation and differentiation, by studying the specific transcripts that are stabilized during infection. This approach will provide mechanistic detail on how Zika virus causes disease in a relevant cellular model system. Furthermore, the study of the Nonsense Mediated Decay pathway provides more detail on an RNA surveillance pathway that is necessary for neurodevelopment. Ultimately, this work could present novel pathways for the development of future therapeutic interventions for microcephaly.