Publication Date


Document Type


Committee Members

Scott Baird (Committee Member), Paula Bubulya (Committee Member), Labib Rouhana (Advisor)

Degree Name

Master of Science (MS)


Precise regulation of gene expression is crucial for the maintenance of pluripotency and proper differentiation of stem cells. Due to their exceptional capacity for stem cell-driven regeneration, planarians are ideal models to dissect mechanisms regulating gene expression that secure stem cell function in vivo. While mechanisms of transcriptional regulation of gene expression in stem cells have been extensively investigated, less is known about regulation at the post-transcriptional level. Exoribonuclease-1 (XRN-1) is a conserved enzyme in eukaryotes that catalyzes 5' to 3' exonucleolytic degradation of RNA. XRN-1 is known to be required for proper regeneration of Dugesia japonica. Here, I validate the requirement of XRN-1 in regeneration of planarian Schmidtea mediterranea and extend the study into identifying the underlying mechanisms that contribute to regeneration-deficiency in animals with reduced xrn-1 mRNA. Expression of S. mediterranea xrn-1 (Smed-xrn-1) in stem cells and in the central nervous system was detected by in situ hybridization. Additionally, targeted disruption of Smed-xrn-1 expression by RNA-interference (RNAi) validated the requirement for XRN-1 function for normal regeneration in S. mediterranea. Interestingly, planarians subjected to Smed-xrn-1 RNAi displayed regeneration deficiencies, but retained their mitotic stem cell populations. Assessment of the requirement XRN-1 during differentiation shows interruptions of stem cell specialization into early progenitor cells. Collectively, these results support the hypothesis that XRN-1 function is to degrade of transcripts whose sustained presence after Smed-xrn-1 RNAi impedes proper stem cell behavior during regeneration. However, it is still unclear of what transcriptional changes occur during regeneration deficiency in Smed-xrn-1 depleted animals and further study is needed to assess the possibility of pleiotropic effects likely due to a broad effect on RNA degradation.

Page Count


Department or Program

Department of Biological Sciences

Year Degree Awarded


Included in

Biology Commons