Authors

S Kramer¹;  ¹ Biozentrum, Lehrstuhl für Zell-und Entwicklungsbiologie, Universität Würzburg, Germany

Discussion

mRNA export is tightly regulated in eukaryotes. Several control systems are in place to ensure that only fully processed mRNA can leave the nucleus. Trypanosomes lack homologues to most proteins that control mRNA export in yeast, have highly unusual symmetrical nuclear pores and unspliced mRNAs are detectable in the cytoplasm. Thus, trypanosomes may have either no quality control system for mRNA export, or the system is not tight.
We visualised mRNAs during nuclear export by intra-molecular multi-colour smFISH. We found that neither transcription, nor splicing needs to be completed for the start of nuclear export. However, unspliced transcripts are enriched in trypanosome-unique granules at the cytoplasmic site of the nuclear pores that resemble stress granules in protein composition, but depend on active transcription rather than translation.
Taken together, our data indicate that trypanosomes lack important nuclear export control checkpoints present in other eukaryotes. Trypanosomes process their mRNAs by trans-splicing and have almost no introns: a tight quality control system may therefore not be necessary.