The nuclear envelope serves as important mRNA surveillance system. In yeast and human, several control systems act in parallel to prevent nuclear export of unprocessed mRNAs. The exact mechanism of mRNA export control still remains unknown; in particular, it is not known whether an RNP is actively selected for nuclear export or actively prevented from export if it is faulty. Trypanosomes lack homologues to most of the involved proteins and their nuclear mRNA metabolism is non-conventional and includes polycistronic transcription and mRNA processing by trans-splicing. We are interested in understanding how mRNAs are exported in the parasites, and, in particular, how unspliced polycistronic mRNAs are prevented from entering the cytoplasm. We have discovered unique RNA granules in trypanosomes that form at the cytoplasmic site of the nuclear pores, when trans-splicing is inhibited. The closer analysis of these granules in nuclear export control is under investigation in the lab. We are employing single molecule FISH techniques to visualise nuclear export of intact and faulty transcripts, and we aim to establish in vivo methods in the future.
Goos, C., Dejung, M., Janzen, C. J., Butter, F., & Kramer, S. (2017). The nuclear proteome of Trypanosoma brucei. PLoS ONE, 12:e0181884.
Kramer S. 2017. Simultaneous detection of mRNA transcription and decay intermediates by dual colour single mRNA FISH on subcellular resolution.Nucleic Acids Res 45:e49.
Kramer S, Piper S, Estevez A, Carrington M. 2016. Polycistronic trypanosome mRNAs are a target for the exosome. Mol Biochem Parasitol205:1–5.
Kramer S, Bannerman-Chukualim B, Ellis L, Boulden EA, Kelly S, Field MC, Carrington M. 2013. Differential localization of the two T. brucei poly(A) binding proteins to the nucleus and RNP granules suggests binding to distinct mRNA pools.PLoS One 8: e54004.
Kramer S, Marnef A, Standart N, Carrington M. 2012. Inhibition of mRNA maturation in trypanosomes causes the formation of novel foci at the nuclear periphery containing cytoplasmic regulators of mRNA fate. J Cell Sci 125: 2896-2909.