Warm_autopsy__mutational_signatures_and_clonal_units

Aims and objectives 1. To produce a ‘first generation map’ of mutational burdens and mutational processes that operate in normal human tissues. 2. To examine clonal units and their distribution across normal human tissues with the emphasis on these particular areas: a) Tissues with an architecturally defined unit: Are architectural structures populated by a progeny derived from a single stem cell? Are clonal units confined to a given architectural structure? Examples of tissues where such approach will be used include prostate gland (acini and ducts), small bowel (crypts), thyroid gland (follicles) and others. b) Tissues without an architecturally defined unit: What is the average size of clonal populations? This group includes stratified/pseudostratified epithelia with a basal layer within which there are stem cells that give rise to a progeny of cells showing upwards migration and lateral expansion (e.g. urothelium, cervical squamous epithelium, respiratory epithelium). This approach can also be used in tissues with a sheet-like cell arrangement, for example brain and adrenal gland. Methods To answer these questions, we will use a range of normal human tissue samples which have already been collected from a single deceased individual. The samples are currently stored in a -80C freezer. Ethanol fixed frozen sections will be prepared from these biopsies. Putative clonal units will be identified and dissected out using laser capture microscopy. DNA extraction will be performed using the in-house (CGP) protease based method. In terms of sequencing methods, the project will be split into 2 phases (2 different approaches): - Phase 1: This part of the project will utilise a combination of low input library preparation (developed by Peter Ellis) and standard whole genome sequencing (HiSeqX). The phase has already started (December 2016). This approach will be particularly useful in investigation of mitotically active tissues. - Phase 2: This part of the project will utilise a combination of low input library method (Peter Ellis) and Bottle-neck sequencing (BotSeqS). BotSeqS is a type of duplex sequencing method that offers a more accurate variant calling and allows genome interrogation at a single cell level. This method is currently being developed and is expected to be implemented in 3-6 months (March-April 2017). This approach will be particularly useful for post-mitotic tissues and tissues without pre-defined architectural units.

Type: Other
Archiver: European Genome-Phenome Archive (EGA)

2 Datasets

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Dataset ID	Description	Technology	Samples
EGAD00001006641	During the course of a lifetime normal human cells accumulate mutations. Here, using multiple samples from the same individuals we compared the mutational landscape in 29 anatomical structures from soma and the germline. Two ubiquitous mutational signatures, SBS1 and SBS5/40, accounted for the majority of acquired mutations in most cell types but their absolute and relative contributions varied substantially. SBS18, potentially reflecting oxidative damage, and several additional signatures attributed to exogenous and endogenous exposures contributed mutations to subsets of cell types. The mutation rate was lowest in spermatogonia, the stem cell from which sperm are generated and from which most genetic variation in the human population is thought to originate. This was due to low rates of ubiquitous mutation processes and may be partially attributable to a low cell division rate of basal spermatogonia. The results provide important insights into how mutational processes affect the soma and germline.	HiSeq X Ten Illumina NovaSeq 6000	1
EGAD00001008764	The single base substitution mutational signatures SBS2 and SBS13, likely caused by APOBEC cytosine deaminases, are common in many human cancer types. However, the stimulus activating APOBEC mutagenesis is unknown and understanding of when it occurs in the progression from normal to cancer cell is limited. Here, as part of a wider survey of human tissues, we whole genome sequenced 342 microdissected normal epithelial crypts from the small intestines of 39 individuals. SBS2/13 mutations were present in 17% normal small intestine crypts and were likely due to APOBEC3A activity. Localised clusters of SBS2/13 mutations (kataegis) were also commonly found. APOBEC mutation burdens were variable between individuals and between crypts from the same individual. Crypts with SBS2/13 often had immediate crypt neighbours without SBS2/13, suggesting that the underlying cause of SBS2/13 is cell-intrinsic rather than a widely distributed microenvironmental exposure, or needs to be permitted by cell-intrinsic conditions. APOBEC mutagenesis occurred throughout the human lifespan, including in young children, and was episodic with a small number of episodes occurring during the life history of a single cell. The results indicate that APOBEC mutagenesis is more common in the small intestine epithelium than in many other cell types, and is an episodic process in vivo initiated or permitted by cell intrinsic factors.	HiSeq X Ten Illumina NovaSeq 6000	408