Limits...
Deadenylation-independent stage-specific mRNA degradation in Leishmania.

Haile S, Dupé A, Papadopoulou B - Nucleic Acids Res. (2008)

Bottom Line: Here, we use the amastin mRNA-an amastigote-specific transcript-as a model and show that a approximately 100 nt U-rich element (URE) within its 3'UTR significantly accounts for developmental regulation.Moreover, our analysis did not reveal a role for decapping in the stage-specific degradation of the amastin mRNA.Overall, these results suggest that degradation of the amastin mRNA of Leishmania is likely to be bi-phasic, the first phase being stage-specific and dependent on an unusual URE-mediated pathway of mRNA degradation.

View Article: PubMed Central - PubMed

Affiliation: Research Centre in Infectious Diseases, CHUL Research Centre and Department of Medical Biology, Faculty of Medicine, Laval University, Quebec, Canada.

ABSTRACT
The life cycle of Leishmania alternates between developmental forms residing within the insect vector (e.g. promastigotes) and the mammalian host (amastigotes). In Leishmania nearly all control of gene expression is post-transcriptional and involves sequences in the 3'-untranslated regions (3'UTRs) of mRNAs. Very little is known as to how these cis-elements regulate RNA turnover and translation rates in trypanosomatids and nothing is known about mRNA degradation mechanisms in Leishmania in particular. Here, we use the amastin mRNA-an amastigote-specific transcript-as a model and show that a approximately 100 nt U-rich element (URE) within its 3'UTR significantly accounts for developmental regulation. RNase-H-RNA blot analysis revealed that a major part of the rapid promastigote-specific degradation of the amastin mRNA is not initiated by deadenylation. This is in contrast to the amastin mRNA in amastigotes and to reporter RNAs lacking the URE, which, in common with most eukaryotic mRNAs studied to-date, are deadenylated before being degraded. Moreover, our analysis did not reveal a role for decapping in the stage-specific degradation of the amastin mRNA. Overall, these results suggest that degradation of the amastin mRNA of Leishmania is likely to be bi-phasic, the first phase being stage-specific and dependent on an unusual URE-mediated pathway of mRNA degradation.

Show MeSH

Related in: MedlinePlus

A proposed model for the stage-specific mRNA degradation of the amastin mRNA. A significant part of the promastigote-specific facilitated degradation of the amastin mRNA (and the LUC-3′UTR mRNA) is URE-dependent, is mostly deadenylation-independent and probably decapping-independent (A). An additional unknown mechanism that is URE-independent (B) might be involved as well because deletion of the URE did not account for all of the stage-specific mRNA regulation at the steady-state levels as indicated in Figure 2. A constitutive deadenylation-dependent pathway (C) is responsible for the decay of more stable mRNAs (LUC-3′UTRΔURE in both developmental forms, and the amastin and LUC-3′UTR mRNAs in amastigotes). A minor sub-population of the amastin and LUC-3′UTR mRNAs in promastigotes is probably degraded via a deadenylation-dependent constitutive pathway.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2275140&req=5

Figure 7: A proposed model for the stage-specific mRNA degradation of the amastin mRNA. A significant part of the promastigote-specific facilitated degradation of the amastin mRNA (and the LUC-3′UTR mRNA) is URE-dependent, is mostly deadenylation-independent and probably decapping-independent (A). An additional unknown mechanism that is URE-independent (B) might be involved as well because deletion of the URE did not account for all of the stage-specific mRNA regulation at the steady-state levels as indicated in Figure 2. A constitutive deadenylation-dependent pathway (C) is responsible for the decay of more stable mRNAs (LUC-3′UTRΔURE in both developmental forms, and the amastin and LUC-3′UTR mRNAs in amastigotes). A minor sub-population of the amastin and LUC-3′UTR mRNAs in promastigotes is probably degraded via a deadenylation-dependent constitutive pathway.

Mentions: Our current model of the amastin mRNA degradation based on this study, and in analogy with the situation in T. brucei, is that two mechanisms are likely to be involved: one that appears to be deadenylation- and decapping-independent, URE-mediated rapid degradation that is developmentally regulated, and the other is constitutive, which is likely to be slower and deadenylation-dependent (Figure 7). This study is the first not only in reporting a URE-mediated degradation in Leishmania but also in attempting to draw the mechanistic basis of differential mRNA degradation in this parasite. The extent to which URE-mediated degradation differs from mammalian ARE-mediated mRNA instability and whether there are species-specific aspects of this mechanism among trypanosomatids remain to be determined.Figure 7.


Deadenylation-independent stage-specific mRNA degradation in Leishmania.

Haile S, Dupé A, Papadopoulou B - Nucleic Acids Res. (2008)

A proposed model for the stage-specific mRNA degradation of the amastin mRNA. A significant part of the promastigote-specific facilitated degradation of the amastin mRNA (and the LUC-3′UTR mRNA) is URE-dependent, is mostly deadenylation-independent and probably decapping-independent (A). An additional unknown mechanism that is URE-independent (B) might be involved as well because deletion of the URE did not account for all of the stage-specific mRNA regulation at the steady-state levels as indicated in Figure 2. A constitutive deadenylation-dependent pathway (C) is responsible for the decay of more stable mRNAs (LUC-3′UTRΔURE in both developmental forms, and the amastin and LUC-3′UTR mRNAs in amastigotes). A minor sub-population of the amastin and LUC-3′UTR mRNAs in promastigotes is probably degraded via a deadenylation-dependent constitutive pathway.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2275140&req=5

Figure 7: A proposed model for the stage-specific mRNA degradation of the amastin mRNA. A significant part of the promastigote-specific facilitated degradation of the amastin mRNA (and the LUC-3′UTR mRNA) is URE-dependent, is mostly deadenylation-independent and probably decapping-independent (A). An additional unknown mechanism that is URE-independent (B) might be involved as well because deletion of the URE did not account for all of the stage-specific mRNA regulation at the steady-state levels as indicated in Figure 2. A constitutive deadenylation-dependent pathway (C) is responsible for the decay of more stable mRNAs (LUC-3′UTRΔURE in both developmental forms, and the amastin and LUC-3′UTR mRNAs in amastigotes). A minor sub-population of the amastin and LUC-3′UTR mRNAs in promastigotes is probably degraded via a deadenylation-dependent constitutive pathway.
Mentions: Our current model of the amastin mRNA degradation based on this study, and in analogy with the situation in T. brucei, is that two mechanisms are likely to be involved: one that appears to be deadenylation- and decapping-independent, URE-mediated rapid degradation that is developmentally regulated, and the other is constitutive, which is likely to be slower and deadenylation-dependent (Figure 7). This study is the first not only in reporting a URE-mediated degradation in Leishmania but also in attempting to draw the mechanistic basis of differential mRNA degradation in this parasite. The extent to which URE-mediated degradation differs from mammalian ARE-mediated mRNA instability and whether there are species-specific aspects of this mechanism among trypanosomatids remain to be determined.Figure 7.

Bottom Line: Here, we use the amastin mRNA-an amastigote-specific transcript-as a model and show that a approximately 100 nt U-rich element (URE) within its 3'UTR significantly accounts for developmental regulation.Moreover, our analysis did not reveal a role for decapping in the stage-specific degradation of the amastin mRNA.Overall, these results suggest that degradation of the amastin mRNA of Leishmania is likely to be bi-phasic, the first phase being stage-specific and dependent on an unusual URE-mediated pathway of mRNA degradation.

View Article: PubMed Central - PubMed

Affiliation: Research Centre in Infectious Diseases, CHUL Research Centre and Department of Medical Biology, Faculty of Medicine, Laval University, Quebec, Canada.

ABSTRACT
The life cycle of Leishmania alternates between developmental forms residing within the insect vector (e.g. promastigotes) and the mammalian host (amastigotes). In Leishmania nearly all control of gene expression is post-transcriptional and involves sequences in the 3'-untranslated regions (3'UTRs) of mRNAs. Very little is known as to how these cis-elements regulate RNA turnover and translation rates in trypanosomatids and nothing is known about mRNA degradation mechanisms in Leishmania in particular. Here, we use the amastin mRNA-an amastigote-specific transcript-as a model and show that a approximately 100 nt U-rich element (URE) within its 3'UTR significantly accounts for developmental regulation. RNase-H-RNA blot analysis revealed that a major part of the rapid promastigote-specific degradation of the amastin mRNA is not initiated by deadenylation. This is in contrast to the amastin mRNA in amastigotes and to reporter RNAs lacking the URE, which, in common with most eukaryotic mRNAs studied to-date, are deadenylated before being degraded. Moreover, our analysis did not reveal a role for decapping in the stage-specific degradation of the amastin mRNA. Overall, these results suggest that degradation of the amastin mRNA of Leishmania is likely to be bi-phasic, the first phase being stage-specific and dependent on an unusual URE-mediated pathway of mRNA degradation.

Show MeSH
Related in: MedlinePlus