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Trans-splicing is a special form of RNA processing in eukaryotes where exons from two different primary RNA transcripts are joined end to end and ligated. It was first discovered in trypanosomatids in 1987 and but was later shown to appear in other eukaryotes[1]. Trans-splicing is less common form of RNA splicing, but has been seen to occur in lower eukaryotes and higher eukaryotes such as rodents and humans [2].

Mechanism

Trans-splicing is similar to cis-splicing which removes introns and ligates the exons from the same primary RNA transcript. In trans-splicing, the donor primary RNA transcript has a spliced leader sequence on the 5’ end and is called SL RNA. This trans-splice site has the same consensus sequence as the intron 3’ splice site on the pre-RNA. Trans splicing happens through a two-step transesterification reaction which forms a Y structure instead of a lariat intermediate which is shown in cis-splicing [1]. The SL RNA has a trimethylguanosine cap on the 5’end which eventually becomes the 5’end of the trans-spliced RNA and which keeps the cap [3]. tRNA can used to mediate trans-splicing of mRNAs [4].

Application

Using RNA splicing to correct mutation that occurs in diseased cells is an emerging therapeutic approach for treating diseases. Trans-splicing is currently under development to treat genetic diseases. It can be used as an effective mean to correct gene mutations on the 5’ and 3’ sites. This method works best if the mutation is on the first or last nucleotide of the intron.Trans-splicing actually benefits over gene replacement therapy because the target gene remains under endogenous control. The trans-splicing molecule only interacts with existing pre-RNA without altering other gene expression [5].

Trans-splicing is being studied as a possible strategy to treat Cystic Fibrosis. It is feasible to reconstruct a working CFTR transcript and replace the gene in the diseased cell, but it unknown if it is possible to make introduce such a large gene into patients cells.[6]

Spliceosome-mediated RNA trans-splicing can also be used to visualize endogenous gene expression in living cells. This can be applied to areas such as cell traffic monitoring, in vivo drug screening and more sensitive non invasive diagnostics [2].

References

1. Riddle DL, Blumenthal T, Meyer BJ, et al., editors. C. elegans II. 2nd edition. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1997. Section III, Trans -Splicing. Available from: http://www.ncbi.nlm.nih.gov/books/NBK20087/

2. Yang Y, Walsh CE (2005). "Spliceosome-mediated RNA trans-splicing". Mol. Ther. 12 (6): 1006–12. doi:10.1016/j.ymthe.2005.09.006. PMID 16226059.

3. Liang XH, Haritan A, Uliel S, Michaeli S (2003) trans and cis splicing in trypanosomatids: mechanism, factors, and regulation. Eukaryot Cell 2: 830–840. doi: 10.1128/ec.2.5.830-840.2003

4. Di Segni G, Gastaldi S, Tocchini-Valentini GP: Cis-and trans-splicing of mRNAs mediated by tRNA sequences in eukaryotic cells. Proc Natl Acad Sci 2008, 105:6864.

5. Havens, M. A., Duelli, D. M. and Hastings, M. L. (2013), Targeting RNA splicing for disease therapy. WIREs RNA, 4: 247–266. doi: 10.1002/wrna.1158

6. Tsui LC, Dorfman R. The cystic fibrosis gene: a molecular genetic perspective. Cold Spring Harb Perspect Med. 2013;3(2):a009472.