NMD3 regulates both mRNA and rRNA nuclear export in African trypanosomes via an XPOI-linked pathway

Area of Science:

• Molecular Biology
• Cell Biology
• Parasitology

Background:

• Gene expression in trypanosomes is primarily regulated post-transcriptionally, with mRNA stability being a key mechanism.
• mRNA nuclear export is a critical regulatory checkpoint, as most mRNA degradation occurs in the cytoplasm.
• The NMD3 protein is known to be involved in ribosomal RNA (rRNA) processing and export in various organisms.

Purpose of the Study:

• To investigate the role of TbNMD3, the trypanosome orthologue of NMD3, in gene regulation.
• To identify novel functions of TbNMD3 beyond its established role in rRNA export.
• To elucidate the mechanisms underlying mRNA regulation by TbNMD3 in trypanosomes.

Main Methods:

• Whole transcriptome RNA sequencing (RNA-seq) was performed on TbNMD3-depleted cells.
• Reporter constructs were used to analyze the regulation of procyclin-associated genes (PAGs).
• Depletion of nuclear export factors XPO1 and MEX67 was employed to compare their effects with TbNMD3 depletion.

Main Results:

• TbNMD3 depletion led to the accumulation of procyclin-associated gene (PAG) transcripts.
• RNA-seq confirmed TbNMD3's regulation of PAG transcripts, with regulation mediated by the 5'UTR of PAG1.
• The observed PAG mRNA accumulation was independent of translational inhibition or enhanced transcription.
• Depletion of XPO1 or MEX67 mimicked the effects of TbNMD3 depletion on PAG mRNAs and nuclear mRNA accumulation.

Conclusions:

• TbNMD3 plays a novel role in the nuclear export of specific mRNA cargos, in addition to its function in rRNA export.
• This suggests a shared pathway for both mRNA and rRNA export in trypanosomes.
• TbNMD3-dependent mRNA export represents a previously unrecognized mechanism for post-transcriptional gene regulation.