Poster abstracts

Poster number 76 submitted by Josiah Liew

Polyadenylation in the Apicomplexa

Ashley T. Stevens (Department of Plant and Soil Sciences, University of Kentucky), Josiah Liew (Department of Plant and Soil Sciences, University of Kentucky), Daniel K. Howe (Department of Veterinary Science, University of Kentucky), Arthur G. Hunt (Department of Plant and Soil Sciences, University of Kentucky)

Abstract:
The process by which the 3’-ends of precursor mRNAs are processed and polyadenylated is an essential step for gene expression in eukaryotes and one at which gene expression may be regulated. In the best characterized of systems, mRNA polyadenylation is mediated by a sizeable complex of proteins that recognizes the polyadenylation signal AAUAAA (and similar A-rich counterparts in yeast and plants), motifs present 5’ (or upstream) of the polyadenylation signal, motifs situated downstream of the poly(A) site, and the actual cleavage/polyadenylation site itself (1). To date, the consensus picture of polyadenylation comes largely from studies conducted in animals and yeast. However, considerable variety in poly(A) signals exists in other organisms (2-4).
With these ideas in mind, a bioinformatics and high throughput sequencing study of polyadenylation in members of the phylum Apicomplexa has been conducted. Analysis of the published genomes for S. neurona, T. gondii, and P. falciparum suggest that the apicomplexan polyadenylation complex is either highly reduced, or consists of several (as yet unidentified) novel subunits. Antibodies raised against the most highly-conserved poly(A) complex subunit (CPSF73) have been used to confirm the presence of the expected polypeptide in one of these organisms, S. neurona. Experiments intended to clarify further the nature of the complex – reduced or vastly different - are in progress.
The nature of the apicomplexan poly(A) signal is unclear. To gain further insight into this, a high throughput sequencing approach was taken, focusing on three apicomplexans - S. neurona, T. gondii, and N. caninum. The results indicate that all three organisms possess a similar, distinctive polyadenylation signal that is reminiscent of that seen in higher plants. These results seem at odds with the bioinformatics study, since the subunits that recognize the analogous polyadenylation signal in mammals are not seen in the bioinformatics study. The resolution of this paradox is the focus of current research.

References:
1. Shi, Y. and Manley, J.L. (2015) The end of the message: multiple protein-RNA interactions define the mRNA polyadenylation site. Genes Dev, 29, 889-897.
2. Franzen, O., Jerlstrom-Hultqvist, J., Einarsson, E., Ankarklev, J., Ferella, M., Andersson, B. and Svard, S.G. (2013) Transcriptome profiling of Giardia intestinalis using strand-specific RNA-seq. PLoS Comput Biol, 9, e1003000.
3. Fuentes, V., Barrera, G., Sanchez, J., Hernandez, R. and Lopez-Villasenor, I. (2012) Functional analysis of sequence motifs involved in the polyadenylation of Trichomonas vaginalis mRNAs. Eukaryot Cell, 11, 725-734.
4. Wodniok, S., Simon, A., Glockner, G. and Becker, B. (2007) Gain and loss of polyadenylation signals during evolution of green algae. BMC Evol Biol, 7, 65.

Keywords: polyadenylation, RNA processing, evolutionary conservation1