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"Poly(A)-Specific Ribonuclease (PARN) and its Role in mRNA Turnover in" Trypanosoma brucei

by
Christopher Utter
Microbiology & Molecular Genetics
B.S. 2001, Lehigh University


Thesis Advisor: Vivian Bellofatto, Ph.D.

Professor

Department: Microbiology & Molecular Genetics

Friday, January 29, 2010
1:30 p.m., ICPH Auditorium


Abstract

Deadenylation is often the rate-limiting event in regulating the population of cellular mRNAs in eukaryotes. Removal of the poly(A) tail initiates mRNA degradation by one of several decay pathways, including deadenylation-dependent decapping followed by 5 to 3 exonuclease decay or 3 to 5 exosome-mediated decay. In trypanosomes, which are parasitic protozoa with complex life cycles, mRNA degradation is important in regulating the expression of a number of differentially expressed genes. Genomics have revealed multiple genes potentially encoding deadenylases similar to those in other eukaryotes. Poly(A)-specific ribonuclease (PARN) is a key deadenylase involved in regulating gene expression in mammals, Xenopus oocytes, and in higher plants. Trypanosomes possess three distinct PARN genes, PARN-1, -2 and -3. Trypanosoma brucei, an important parasite of humans and domestic cattle, expresses each of the three PARN genes in at least two of its life cycle stages. Two of the PARNs, TbPARN-1 and TbPARN-3, are shown to be active deadenylases. To determine the roles of TbPARN-1 and TbPARN-3, the proteins were overexpressed in procyclic and bloodstream form trypanosomes. The effects on steady state levels of the entire mRNA population were analyzed using microarrays. Interestingly, a subset of mRNAs was selectively affected. This suggests that TbPARNs regulate the levels of specific mRNAs, and do not function as general deadenylases. Within this subset, is a family of developmentally regulated, life stage-specific (epimastigote-specific) mRNAs that encode surface coat proteins. Overexpression of TbPARN-1 results in an increased rate of decay among these mRNAs, indicating that TbPARNs contributes to the post-transcriptional control mechanisms active in trypanosomes.


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