Roles of aTrypanosoma brucei5′→3′ exoribonuclease homolog in mRNA degradation

Abstract

The genome of the kinetoplastid parasite Trypanosoma brucei encodes four homologs of the Saccharomyces cerevisiae 59/39 exoribonucleases Xrn1p and Xrn2p/Rat1p, XRNA, XRNB, XRNC, and XRND. In S. cerevisiae, Xrn1p is a cytosolic enzyme involved in degradation of mRNA, whereas Xrn2p is involved in RNA processing in the nucleus. Trypanosome XRND was found in the nucleus, XRNB and XRNC were found in the cytoplasm, and XRNA appeared to be in both compartments. XRND and XRNA were essential for parasite growth. Depletion of XRNA increased the abundances of highly unstable developmentally regulated mRNAs, perhaps by delaying a deadenylation-independent decay pathway. Degradation of more stable or unregulated mRNAs was not affected by XRNA depletion although a slight decrease in average poly(A) tail length was observed. We conclude that in trypanosomes 59/39 exonuclease activity is important in degradation of highly unstable, regulated mRNAs, but that for other mRNAs another step is more important in determining the decay rate.

Insights into the regulation of GPEET procyclin during differentiation from early to late procyclic forms of Trypanosoma brucei

“…Several studies revealed a biphasic decay pattern for EP1 mRNA in bloodstream forms and identified the nucleases involved [27][28][29]46]. In one of our experiments, a decay pattern reminiscent of biphasic decay kinetics was found for GPEET mRNA in late PF (with only 0.4% GPEET-positive cells) (Fig.…”

“…S1, panels d 0, d 2, d 6, d 11). Transient rises up to 2 h have been observed in kinetoplastids [40] and have been attributed to a pool of precursors that continue to be spliced after transcription is inhibited [27]. We propose that the prolonged rise observed with procyclin mRNAs is due to their extraordinary stability.…”

“…The stability of bulk procyclin mRNA was previously measured in bloodstream forms and PF [24,25], and turnover of EP1 mRNA in bloodstream forms was determined by means of reporter mRNAs [26][27][28][29][30]. However, these studies either did not discriminate between GPEET and EP, or lacked data on GPEET mRNA in general; in addition, procyclin mRNA stability has never been assessed during the transition from early to late PF.…”

mRNA stability in the nucleus

“…Rat1p was initially identified in S. cerevisiae and then found to be conserved in all eukaryotes (Amberg et al, 1992;Shobuike et al, 1995;Yoo et al, 2000;West et al, 2004;Li et al, 2006). It functions essentially in RNP II transcription termination to remove the long aberrant mRNAs which associate with a chromosome and might cause deleterious effects in cells (Proudfoot, 2011).…”

Functional Genomics and Insights into Trypanosoma cruzi Gene Expression Regulation

“…In fact, active deadenylation systems have been found in trypanosome cells [23,24], including the description of the enzymes triggering mRNA degradation. The mechanism involves mRNA degradation from both ends, by XRN1-related exoribonucleases (5'-3'direction) and the exosome (3'-5'direction), after removal of the poly(A) tail and the 5' Cap [25,26]. However, data related to the exosome machinery were reported for T. brucei alone.…”