# Differential regulatory role of AU-rich and GU-rich elements in Trypanosoma brucei

## TL;DR

This study explores how AU- and GU-rich elements in Trypanosoma brucei regulate gene expression differently across life stages.

## Contribution

The study identifies gene-specific and context-dependent regulatory roles of AREs and GREs in T. brucei, along with a potential GRE-binding protein.

## Key findings

- AU- and GU-rich elements are enriched in 3′UTRs of developmentally regulated mRNAs in T. brucei.
- GREs in ICP and TOP2 3′UTRs destabilize transcripts in procyclic forms but enhance expression in bloodstream forms.
- DRBD2 is a potential GRE-binding protein, and its knockdown reduces ICP mRNA abundance in procyclic trypanosomes.

## Abstract

Post-transcriptional regulation is the predominant mode of gene expression control in Trypanosoma brucei, yet the underlying regulatory elements and proteins remain poorly defined. AU- and GU-rich elements (AREs and GREs) are common post-transcriptional regulatory motifs. To investigate their roles in T. brucei, we analyzed transcriptomic datasets and extracted 5,840 genes with defined 5′ and 3′ untranslated regions (UTRs), including 327 that are developmentally regulated between the parasite’s two life stages. Computational analysis revealed that AU- and GU-rich elements are widespread and enriched in the 3′UTRs of developmentally regulated mRNAs as well as in transcripts with long half-lives. Functional assays demonstrated regulatory activity of AREs and GREs within the 3′UTRs of five representative genes (ICP, TOP2, MCC-β, PK, and KREPB6), with differential effects on reporter expression. Notably, the GREs in the ICP and TOP2 3′UTRs destabilized reporter transcripts in procyclic-form trypanosomes but enhanced expression in bloodstream forms. RNA pulldown assays further identified DRBD2 as a potential GRE-binding protein, and DRBD2 knockdown reduced ICP mRNA abundance in procyclic trypanosomes. Collectively, these findings demonstrate that AREs and GREs are critical regulatory elements in T. brucei, exhibiting gene-specific and context-dependent functions. Elucidating their regulatory roles and identifying additional binding proteins will provide new insights into the mechanisms of post-transcriptional control in this parasite.