Pre-messenger RNA splicing is a critical step in eukaryotic gene expression. It consists in the splicing of exons and the release of introns composing the pre-messenger RNA to allow the formation of messenger RNA. This reaction is performed within the spliceosome, a macro-complex whose remodeling is very dynamic. The spliceosome includes 5 snRNPs each composed of a small nuclear RNA (U1, U2, U4, U5 or U6) and proteins. At each splicing reaction, the spliceosome assembles around an intron, performs the splicing reaction and then must disassemble to perform its function on a new intron. Recycling of the different snRNPs is thus a fundamental process of the spliceosome cycle.
In yeast, the RNA-binding protein NTR1 is the ortholog of the human Tuftelin-interacting protein 11/TFIP11. NTR1 is involved in the intron release step, in partnership with the helicase prp43-t the ortholog of the human protein DHX15. In human cells, functional inactivation of TFIP11 induces splicing defects and is associated with arrest in mitosis followed by activation of apoptosis, defects that are not observed upon inactivation of DHX15, indicating a role of TFIP11 independent of DHX15 in human cells.
This study published in Nature Communication shows the involvement of TFIP11 in spliceosome re-assembly in Cajal Bodies and in snRNPU6 maturation. This demonstration is based on the identification of RNAs directly associated with TFIP11 by iCLIP-SEQ. We have observed that TFIP11 binds preferentially to small non-coding RNAs UsnRNA, scaRNA (small Cajal body RNAs) and SnoRNA and thereby controls certain modifications of U6 RNA, the stability of the U4/U6.U5 tri-SnRNP and more globally controls spliceosome assembly.
This study highlights the essential role of TFIP11 in the life cycle of the spliceosome. Its inactivation is the source of many splicing defects associated with division defects leading to cell death. Pharmacological modulation of TFIP11 activity by small molecules could be an avenue of action in splicing-dependent pathologies.
Team : Genetic Expression and Development Team, IGDR.