Oral Presentation 39th Annual Lorne Genome Conference 2018

Essential roles for minor class splicing in development and cancer (#25)

Karen Doggett 1 , Ben B Williams 1 , Sebastian Markmiller 2 , Kimberly J Morgan 1 , Kate D Sutherland 1 , Robert J O'Donoghue 3 , Tracy L Putoczki 1 , Matthias Ernst 3 , Joan K Heath 1
  1. Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. Department of Surgery, Royal Melbourne Hospital, Parkville, Vic, Australia
  3. Cancer and Inflammation, Olivia Newton John Cancer Research Institute, Melbourne, Vic, Australia

Splicing is an essential step in eukaryotic gene expression. While a clear majority of introns is excised by major class (or U2-dependent) splicing, the appropriate excision of a very small subset of introns (<0.35% in human) depends on minor class (or U12-dependent) splicing. However, these introns are highly conserved and genes that contain minor class introns are over-represented in functions and pathways related to essential cellular processes, such as cell cycle, DNA replication and repair, RNA processing, and important signalling pathways including RAS/MAPK signalling.

Our characterisation of a zebrafish mutant, caliban, lacking a specific minor class spliceosome component, Rnpc3, revealed minor class splicing was vital for vertebrate development. Transcriptome analysis of rnpc3-/- larvae demonstrates that minor class splicing is required for the proper expression of genes involved in transcription, splicing and nuclear export. Furthermore, since these genes are essential for the growth and division of rapidly proliferating cells, we hypothesized that efficient minor class splicing would also be crucial for cancer cells. By utilizing a krasG12V-driven zebrafish hepatocellular carcinoma model we found that heterozygous loss of rnpc3 restricted liver hyperplasia.

In addition, we generated germline and conditional mouse models of Rnpc3 deficiency to investigate the importance of minor class splicing during mammalian development and in tumour-prone mice. Rnpc3 is indispensable for mouse development and systemic loss via inducible deletion in adult mice results in rapid weight loss, leukopenia and atrophy of the gastrointestinal tract. Remarkably, we found that Rnpc3 heterozygosity in mice decreases gastric and lung tumour burden and also prolongs survival of Pten heterozygous mice, which spontaneously develop large lymphomas.

This study presents the first mouse models of minor class splicing deficiency and establishes that this hitherto under-appreciated process is indispensable throughout life and may represent a useful, clinically relevant target for a broad spectrum of cancer types.