Hall, A. E. | bioRxiv Science

bioRxiv2025

NSUN2 drives intestinal stem cell expansion and colorectal tumour initiation via MAPK/ERK signalling

Colorectal cancer is initiated by loss of the APC gene, which drives expansion of LGR5+ intestinal stem cell (ISC) populations. Whilst LGR5+ ISC expansion is a critical step for tumour initiation and progression, its regulation is poorly understood. Emerging evidence suggests post-transcriptional RNA modifications play a key role in cancer biology, but their role in CRC initiation has not been explored. Here, we identify the m5C methyltransferase NSUN2 as a key regulator of ISC expansion and intestinal tumourigenesis. NSUN2 is upregulated in multiple CRC mouse models and human tumours and its depletion impairs ISC expansion and hyperproliferation, leading to reduced tumour initiation. Transcriptome-wide bisulphite sequencing revealed that NSUN2-mediates m5C methylation on mRNAs encoding key ISC regulators and components of the MAPK/ERK pathway. Mechanistically, loss of NSUN2 reduces ERK phosphorylation in Apc-deficient models and oncogenic KrasG12Dexpression is sufficient to restore ERK signalling and rescue ISC expansion. Together, this establishes NSUN2 as a key regulator of ISC-driven CRC initiation and describes a novel molecular mechanism linking m5C methylation to MAPK driven stem cell transformation.

cancer biology↗

bioRxiv2023

C. elegans Afadin is required for epidermal morphogenesis and functionally interfaces with the cadherin-catenin complex and RhoGAP PAC-1/ARHGAP21

During epithelial morphogenesis, the apical junctions connecting cells must remodel as cells change shape and make new connections with their neighbors. In the C. elegans embryo, new apical junctions form when epidermal cells migrate and seal with one another to encase the embryo in skin ( ventral enclosure), and junctions remodel when epidermal cells change shape to squeeze the embryo into a worm shape ( elongation). The junctional cadherin-catenin complex (CCC), which links epithelial cells to each other and to cortical actomyosin, is essential for C. elegans epidermal morphogenesis. RNAi genetic enhancement screens have identified several proteins that interact with the CCC to promote epidermal morphogenesis, including the scaffolding protein Afadin (AFD-1), whose depletion alone results in only minor morphogenesis defects. Here, by creating a null mutation in afd-1, we show that afd-1 provides a significant contribution to ventral enclosure and elongation on its own. Unexpectedly, we find that afd-1 mutant phenotypes are strongly modified by diet, revealing a previously unappreciated maternal nutritional input to morphogenesis. We identify functional interactions between AFD-1 and the CCC by demonstrating that E-cadherin is required for the polarized distribution of AFD-1 to cell contact sites in early embryos. Finally, we show that afd-1 promotes the enrichment of polarity regulator and CCC-interacting protein PAC-1/ARHGAP21 to cell contact sites, and identify genetic interactions suggesting that afd-1 and pac-1 regulate epidermal morphogenesis at least in part through parallel mechanisms. Our findings reveal that C. elegans AFD-1 makes a significant contribution to epidermal morphogenesis and functionally interfaces with core and associated CCC proteins.

developmental biology↗