Crypt-restricted metallothionein immunopositivity in murine colon: validation of a model for studies of somatic stem cell mutation.
The ability to visualize the cellular effects of a somatic mutation is relevant to studies of cell kinetics and carcinogenesis. In the colon, mutagen administration leads to scattered crypt-restricted loss of activity of the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD); it has been shown that this is due to somatic mutation in the G6PD gene. Mutagen-induced crypt-restricted immunopositivity for metallothionein (MT) has been reported in one study in the mouse colon; if this is also due to somatic mutation, it provides a simple method for studying the phenomenon which could be carried out on paraffin sections. This study shows that, as in the G6PD model, the frequency of crypt-restricted immunopositivity for MT is very low in untreated animals, but increases proportionately with the dose of mutagen administered. There is a good overall correlation of a range of MT-positive crypt frequencies with those derived from studies using G6PD. As with the G6PD model, the MT-positive crypt phenotype evolves over time after mutagen administration; initially individual crypts include both positive and negative phenotype cells, but later almost all involved crypts are composed entirely of MT-positive cells. The frequency of MT-positive crypts stabilizes after a few weeks and remains at the same level 6 months later. All these observations are qualitatively identical to those found using the G6PD model and provide strong evidence that stable, crypt-restricted immunopositivity for MT results from a mutation affecting expression of the metallothionein gene in a colonic stem cell. This model will provide a useful tool to study factors influencing stem cell mutation frequency and cell kinetics in the colon.
Anne Cook
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TCRG, University of Cambridge, Strangeways Research Laboratory, Wort's Causeway, UK.
Williams
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Anne Thomas
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D000818:Animals; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005038:Ethylnitrosourea / Q000494:pharmacology; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D008668:Metallothionein / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008957:Models, Genetic; D009153:Mutagens / Q000494:pharmacology; D009154:Mutation; D010641:Phenotype; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism*
D009153:Mutagens; D008668:Metallothionein; D005954:Glucosephosphate Dehydrogenase; D005038:Ethylnitrosourea