Intestinal stem cells protect their genome by selective segregation of template DNA strands.
The stem cells in the crypts of the small intestinal mucosa divide about a thousand times during the lifespan of a laboratory mouse, and yet they show little evidence of any decline in proliferative potential and rarely develop carcinogenic mutations, suggesting that their genome is extremely well protected. Protection against DNA-replication-induced errors can be achieved by the selective sorting of old (template) and new DNA strands with all template strands retained in the stem cell line. The template strands in the stem cells can be labelled during development or during tissue regeneration using tritiated thymidine ((3)HTdR). Labelling newly synthesised strands with a different marker (bromodeoxyuridine, BrdUrd) allows segregation of the two markers to be studied. Template strand label is retained ((3)HTdR), whereas label in the newly synthesised strands (BrdUrd) is lost following the second division of the stem cell. Random errors may occur in the template strands owing to environmental elements. These are protected against by the altruistic cell suicide (apoptosis) of the cells incurring such errors. A final level of protection for the tissue compensates for excessive deletion of stem cells via the apoptosis pathway. This is achieved by a hierarchical age structure in the stem cell compartment, with some cells being able to efficiently repair DNA damage and hence being more radioresistant. The presence of these protective mechanisms ensures that the small intestine rarely develops cancer and that stem cells can sustain the extensive cell proliferation needed during life.
Potten
Christopher S
CS
Epithelial Biology Department, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Wilmslow Road, Manchester M9 4BX, UK. potten@epistem.co.uk
Owen
Gary
G
Booth
Dawn
D
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000528:radiation effects; D001973:Bromodeoxyuridine; D002455:Cell Division / Q000235:genetics* / Q000528:radiation effects; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000528:radiation effects; D020090:Chromosome Segregation / Q000235:genetics* / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics* / Q000528:radiation effects; D004261:DNA Replication / Q000235:genetics* / Q000528:radiation effects; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D005720:Gamma Rays; D016678:Genome; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D007414:Intestinal Neoplasms / Q000235:genetics; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D051379:Mice; D008815:Mice, Inbred Strains; D009154:Mutation / Q000235:genetics / Q000528:radiation effects; D019879:Paneth Cells / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D013698:Templates, Genetic
D001973:Bromodeoxyuridine