Biology subjects

Morison, I. M.

Publications and source records attributed to Morison, I. M..

3 recordsLinked to original sources

bioRxiv2021

Pronounced sequence specificity of the TET enzyme catalytic domain guides its cellular function

TET (ten-eleven translocation) enzymes catalyze the oxidation of 5-methylcytosine bases in DNA, thus driving active and passive DNA demethylation. Here, we report that the catalytic cores of mammalian TET enzymes favor CpGs embedded within bHLH and bZIP transcription factor binding sites, with 250-fold preference in vitro. Crystal structures and molecular dynamics calculations show that sequence preference is caused by intra-substrate interactions and CpG flanking sequence indirectly affecting enzyme conformation. TET sequence preferences are physiologically relevant as they explain the rates of DNA demethylation in TET-rescue experiments in culture and in vivo within the zygote and germline. Most and least favorable TET motifs represent DNA sites that are bound by methylation-sensitive immediate-early transcription factors and OCT4, respectively, illuminating TET function in transcriptional responses and pluripotency support. One-Sentence SummaryThe catalytic domains of the enzymes that facilitate passive and drive active DNA demethylation have intrinsic sequence preferences that target DNA demethylation to bHLH and bZIP transcription factor binding sites.

molecular biology↗

bioRxiv2021

The mouse papillomavirus epigenetic signature is characterised by DNA hypermethylation after lesion regression

The {beta} genus of human papillomaviruses (HPVs) infect cutaneous epidermis. They contribute to the development of cutaneous squamous cell carcinoma (cSCC) in individuals with epidermodysplasia verruciformis, and increase susceptibility to UV-induced cSCC. This has been demonstrated in UV-exposed mice previously infected with mouse papillomavirus (MmuPV1). However, the mechanism by which {beta}-HPVs contribute to cSCC is unclear. We propose that viral infection leaves a DNA methylation signature following resolution of the active lesion that may contribute to increased susceptibility to UV-induced cSCC. To test this, we carried out Reduced Representation Bisulphite Sequencing on DNA from tail skin of mice with actively infected lesions, MmuPV1-infected then healed lesions (regressed infection), and mock-infected control mice. Genome-scale DNA methylation libraries were generated and analysed for differentially methylated regions throughout the genome, and for HPV sequences. We found that DNA of active lesions was not differentially methylated compared to matched control mice. In contrast, 834 differentially methylated fragments were identified in regressed lesions compared to mock-infected control skin. An analysis of MmuPV1 viral DNA demonstrated retention of viral DNA in some of the lesions that had regressed. Overall, the viral sequences identified showed over-representation of sequences from the E4 region. The DNA hypermethylation that we found in regressed MmuPV1 lesions may be a factor in the increased susceptibility of mice to UV-induced cSCC. AUTHOR SUMMARYPapillomavirus infections can be asymptomatic, can cause warts, and in some cases can lead to cancer. There is direct evidence for mouse papillomavirus infection resulting in increased susceptibility to UV-induced cutaneous squamous cell carcinoma in a mouse model. We propose that DNA methylation following viral infection may contribute to the increased susceptibility. We describe the DNA methylation landscape during an active infection with mouse papillomavirus and following regression of the lesion. We found that there were very few differentially methylated DNA fragments during active infection. In contrast, over 800 differentially methylated DNA fragments were identified following regression of the lesion. This is the first description of the genome-wide DNA methylation landscape for mouse papillomavirus, to our knowledge. The dramatic DNA hypermethylation that we observe following resolution of infection may contribute to a hit and run mechanism for the increased susceptibility to UV-induced cancer by papillomaviruses.

pathology↗

bioRxiv2019

BET inhibition prevents aberrant RUNX1 and ERG transcription in STAG2 mutant leukaemia cells.

Mutations in the subunits of the cohesin complex, particularly in the STAG2 subunit, have been identified in a range of myeloid malignancies, but it is unclear how these mutations progress leukaemia. Here, we created isogenic K562 erythromyeloid leukaemia cells with and without the known leukemic STAG2 null mutation, R614*. STAG2 null cells acquired stem cell and extracellular matrix gene expression signatures that accompanied an adherent phenotype. Chromatin accessibility was dramatically altered in STAG2 null K562 cells, consistent with gene expression changes. Enhanced chromatin accessibility was observed at genes encoding hematopoietic transcription factors, ERG and RUNX1. Upon phorbol 12-myristate 13-acetate (PMA)-induced megakaryocytic differentiation, STAG2-null cells showed precocious spike in RUNX1 transcription from its P2 promoter. A similar precocious spike was observed in transcription of ERG. Interestingly, spikes in RUNX1-P2 and ERG only occurred as immediate early response to differentiation induction. Treatment of STAG2 null cells with enhancer-blocking BET inhibitor, JQ1, dampened precocious RUNX1 P2 expression and led to a complete loss of RUNX1 P1 and ERG transcription during PMA stimulation in both parental and STAG2 null K562 cells. These results suggest that precocious RUNX1 and ERG expression in STAG2 null cells is enhancer-driven. Furthermore, JQ1 treatment reduced stem cell-associated KIT expression in STAG2 null cells. We conclude that STAG2 depletion in leukemic cells amplifies an enhancer-driven transcriptional response to differentiation signals, and this characteristic is dampened by BET inhibition. The results have relevance to the development of therapeutic strategies for myeloid leukaemia

cancer biology↗