Mitochondrial DNA mutations are established in human colonic stem cells, and mutated clones expand by crypt fission - PubMed (original) (raw)

. 2006 Jan 17;103(3):714-9.

doi: 10.1073/pnas.0505903103. Epub 2006 Jan 6.

Sean L Preston, Paul J Tadrous, Robert W Taylor, Martin J Barron, Dahmane Oukrif, Simon J Leedham, Maesha Deheragoda, Peter Sasieni, Marco R Novelli, Janusz A Z Jankowski, Douglass M Turnbull, Nicholas A Wright, Stuart A C McDonald

Affiliations

Mitochondrial DNA mutations are established in human colonic stem cells, and mutated clones expand by crypt fission

Laura C Greaves et al. Proc Natl Acad Sci U S A. 2006.

Abstract

The understanding of the fixation of mutations within human tissues and their subsequent clonal expansion is a considerable problem, of which little is known. We have previously shown that nononcogenic mutations in the mitochondrial genome occur in one of a number of morphologically normal colonic crypt stem cells, the progeny of which later occupy the whole crypt. We propose that these wholly mutated crypts then clonally expand by crypt fission, where each crypt divides into two mutated daughter crypts. Here we show that (i) mutated crypts in the process of fission share the same mutated mitochondrial genotype not present in neighboring cytochrome c oxidase-positive crypts (the odds of this being a random event are >or=2.48 x 10(9):1); (ii) neighboring mutated crypts have the same genotype, which is different from adjacent cytochrome c oxidase-positive crypts; (iii) mutated crypts are clustered together throughout the colon; and (iv) patches of cytochrome c oxidase-deficient crypts increase in size with age. We thus demonstrate definitively that crypt fission is the mechanism by which mutations spread in the normal human colon. This has important implications for the biology of the normal adult human colon and possibly for the growth and spread of colorectal neoplasms.

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Figures

Fig. 1.

Fig. 1.

Both arms of a cytochrome c oxidase-deficient crypt in fission share identical mutations. (a–i) Serial sections were made of a single crypt in fission, and single cells were isolated from each arm and from a single neighboring cytochrome c oxidase-positive crypt. Cells from both arms of the cytochrome c oxidase-deficient crypt in fission had a common 4733 T>C transition j is the neighboring cytochrome c oxidase-positive crypt, and k is from the deficient crypt in fission.

Fig. 2.

Fig. 2.

Single cells were isolated from each of the cytochrome c oxidase-deficient crypts and from adjacent cytochrome c oxidase-positive crypts. In one patient, each cytochrome c oxidase-deficient cell had a 6277 A>G transition (a) which is not present in the cytochrome c oxidase-positive cells (b). In another patient, each cytochrome c oxidase-deficient cell had a 7275 T>C transition (c) and a C311 insertion (e) not present in the cytochrome c oxidase-positive cells (d and f).

Fig. 3.

Fig. 3.

Analysis of

clan

-generated data. (a) The observed RR for any image was >1 in all patients except patient 11 (40 years of age) who had very few mutated crypts. (b) Observed versus randomly generated data for RR, χ2, and Nprop (91.18%, 82.35%, and 88.24%, respectively) for all images achieved significance at the 95% level. (c) All images were analyzed by two independent researchers in a blinded fashion, and no intraobserver differences were found [correlation coefficient (_R_2) of 0.85].

Fig. 4.

Fig. 4.

Mean patch size of cytochrome c oxidase-deficient crypts increases with age. Patients have been grouped according to decade (31–40, 41–50, 51–60, 61–70, 71–80, and 81–90). Results are ± SEM. Although individual deficient crypts were observed in patients under the age of 40, no patches of two or more deficient crypts were seen. _R_2 = 0.8741, and the equation of best-fit curve is y = 0.20090.03295x.

Fig. 5.

Fig. 5.

A proposed model of how DNA mutations spread in the human colon. The initial mutation can occur anywhere within the epithelium but can persist only in stem cells. Occasionally, a stem cell carrying a DNA mutation can dominate the crypt, leading to all cells within that crypt also carrying the mutation. At some point, this crypt will divide by fission, and this process will carry on through the life of the host. If the mutation is prooncogenic, this may affect the rate at which this occurs, resulting in a rapid spread of potentially cancerous mutations.

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