Luiselli D, Franceschi C. Garagnani P. Space/Population and Time/Age in DNA methylation variability in humans: a study on
IGF2/H19 locus in different Italian populations and in mono‐ and di‐zygotic twins of different age. AGING: this issue
In post-genomic era attention has been focused on the
characterization of the human DNA “methylome” at
single nucleotide resolution. It is a particularly difficult
goal to achieve as methylation profiling is different in
tissues and cells of the same individual. 5-
Methylcytosine is considered the “fifth base” of DNA
as it introduces an epigenetic code on genome which is
defined during development. Nutrition, environment
and style of life have an impact on the “methylome” and
the introduction of anomalous methyl groups in
sequences that have to be maintained unmethylated
and/or demethylation of chromatin regions which are
usually methylated drive the biological events
associated with pathologies. The same anomalies in
methylation patterns occur with age so an in-depth
knowledge of these changes will help us to individuate
what leads to the passage from successful ageing to one
in which there is the onset of disease . Data from
Franceschi’s group are focused on ageing and the
cohorts of individuals are selected in order to establish
whether variability in DNA methylation patterns is to
ascribe to age of individuals rather than to their
geographical dimension. Notably, in this study
monozygotic and dizygotic twins of ages ranging from
22 to 97 years are also enrolled.
Four regions, located at the Igf2/H19 imprinted locus,
were analyzed including the CpG island present in
differentially methylated region 2 (DMR2) and the
nearby 5’ shore, two fragments never investigated up to
now. Authors conclude that the shore is the one in
which the scatter in methylation variability during
ageing is more evident.
Shore regions, which localize in proximity of CpG
islands at 200-2000 kb away from them, are of
particular interest as involved in gene expression
regulation through the DMRs often located within them
A long-range looping interaction is involved in the
control of imprinting at maternally inherited allele at the
Igf2/H19 gene locus. An interesting hypothesis for sus-
ceptibility to epimutation of this shore region in aged
individuals is that its position inside the loop is
topologically responsible for its availability to change
the methylation profile. Although the higher order
chromatin organization at Igf2/H19 locus is well
assessed in mice, less information is available in
Anyway, the analysis of data about chromatin structure
from the ENCODE consortium, accessible at the UCSC
Genome Browser (http://genome.ucsc.edu/) [3, 4],
indicates a distinctive chromatin feature of this shore
region which corresponds to an open, DNAaseI
hypersensitive chromatin domain characterized by an
early S-phase replication.
As chromatin structure affects the susceptibility to DNA
damage, the chromatin shape of the shore could be the
reason for its susceptibility to epimutation. An
important link was found between DNA damage,
homology directed repair and DNA methylation ,
suggesting that DNA-methyltransferase 1(DNMT1),
which is recruited to repair sites following double-
strand DNA breaks , marks the repaired segments
superimposing novel methylation profile.
Another interesting hypothesis rises from the early
replication timing of this shore. The maintenance of
DNA methylation patterns during DNA replication
requires the function of DNMT1 which is brought to the
replication fork through a direct interaction with
Proliferating Cell Nuclear Antigen protein (PCNA).
Interestingly, DNMT1 forms a complex at replication
foci only during late stages of S-phase when methylated
DNA is replicated. Thus, the controlled recruitment of
DNMT1 into replication forks is an important
component in the perpetuation of DNA methylation
patterns and S-phase abnormalities could affect
methylation patterns by altering the replication timing
of sequences. The biological event able to disrupt
DNMT1 function in S phase could be poly(ADP-
ribosyl)ation. It has been found that competitive
inhibition of PARPs leads to hyperexpression of
Why is DNA methylation of Igf2 CpG island shore affected during ageing?
Paola Caiafa and Michele Zampieri
Comment on: Pirazzini C, Giuliani C, Bacalini MG, Boattini A, Capri M, Fontanesi E, Marasco E, Mantovani V, Pierini M, Pini E,
www.impactaging.com AGING, July 2012, Vol. 4, No 7
www.impactaging.com 448 AGING, July 2012, Vol.4 No.7
DNMT1 in G1/early S phase, increases the amount of Download full-text
DNMT1 that co-immunoprecipitates with PCNA in this
phase and causes DNA hypermethylation .
Interestingly, reduced levels of poly(ADP-ribosyl)ation
enzymes PARP1 and 2 and poly(ADP-ribosyl)ation
activity have been associated with ageing [8, 9].
In conclusion, changes of methylation profile at Igf2
CpG island shore observed during ageing could be due
to the loss of local epigenetic control of this region. The
understanding of molecular mechanism(s) involved in
the protection of the methylation pattern of this shore
could provide important information about the
participation of epigenetics in ageing and disease.
Paola Caiafa, PhD
Department of Cellular Biotechnologies and Hematology, Faculty
of Pharmacy and Medicine, Sapienza University of Rome, 00161
Received: 7/26/12; Published: 8/01/12
1. Calvanese V, Lara E, Kahn A, et al. Ageing Res Rev. 2009; 8:
2. Doi A, Park IH, Wen B, et al. Nat Genet. 2009; 41: 1350‐1353.
3. Rosenbloom KR, Dreszer TR, Pheasant M, et al. Nucleic Acids
Res. 2010; 38: D620‐625.
4. Celniker SE, Dillon LA, Gerstein MB, et al. Nature. 2009; 459:
5. Cuozzo C, Porcellini A, Angrisano T, et al. PLoS Genet. 2007; 3:
6. Mortusewicz O, Schermelleh L, Walter J, et al. Proc Natl Acad
Sci U S A. 2005; 102: 8905‐8909.
7. Caiafa P, Zampieri M. J Cell Biochem. 2005; 94: 257‐265.
8. Chevanne M, Calia C, Zampieri M, et al. Rejuvenation Res.
9. Beneke S, Bürkle A. Nucleic Acids Res. 2007; 35: 7456‐7465.
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