Transgenerational
epigenetic inheritance of
longevity in C. elegans
by Greer et. al. 2011
Ray Xiao
Jake Gianuzzi
Abbie Ho
Important Concepts/Key Terms
-C. elegans as a model organism
-Brief review of chromatin and histone
-’Reprogramming’ the Epigenome
-Main purpose of the paper
-WDR-5
-SET-2
-ASH-2
C. elegans
why is it a good model organism?
-relatively inexpensive
-remain transparent throughout their life cycle
-C. elegans are very fertile
-short maturation period
-first multicellular organism that has complete sequenced
genomes
Chromatin & Histone
-Chromatin is the combination or complex of
DNA and proteins that make up the contents
of the nucleus of a cell.
-Functions:
1) to package DNA into a smaller volume to fit in the cell
2) to strengthen the DNA to allow mitosis
3) to prevent DNA damage
4) to control gene expression and DNA replication
Chromatin & Histone
-Histones are the primary protein
components of chromatin that
compact the DNA
-Histones are modified by various
post-translational modification to
alter DNA packing
Reprogramming the Epigenome
“..changes in chromatin states in the parental generation could be
incompletely reprogrammed in the next generation and thereby affect
lifespan of descendants.” -Abstract
What is meant by ‘reprogrammed’?
-Removal of (most) epigenetic marks established during the development of a mature organism
Why is ‘reprogramming’ important (to the organism and its progeny)?
-It is important that epigenome-wide reprogramming does not happen during a mature organisms
life so that its epigenome is ‘remembered’.
-It is important that most epigenetic marks of a mature individual are irrelevant to the next
generation, the slate is wiped clean to allow gametic epigenomes to endow the capacity to
differentiate into all cell types of a fully developed organism.
Objectives
What do they study? (What molecule or property of molecules)
H3K4me3 in C. Elegans
What do they alter experimentally to study this molecule/property?
Perturbation of the H3K4me3 regulatory complex (ASH2, WDR5, SET2) only in the
parental generation --could it affect longevity of progeny across generations?
-The results show that deficiencies in H3K4me3
chromatin modifiers ASH-2, WDR-5, SET-2 in the
parental generation extend the lifespan of descendants
for several generations.
Key Players
COMPASS: A heptameric protein complex, consists of
SET1: responsible for the bulk of H3K4 methylation - and associated proteins
SET2: Histone methyltransferase
WDR-5: a conserved regulatory component of ASH-2
ASH-2: a component for the conversion of H3K4me2 to H3K4me3
The Active Mark
H3K4me3 is an ‘active mark’, associated with
active chromatin, and its excess is
detrimental to longevity.
How could this be achieved? (i.e. molecular
mechanism?)
Chromatin modifier WDR-2
Figure 1.
Chromatin modifier SET-2
Figure 2.
Fig3
How was the ash-2 knockdown different than that of wdr-5 and set-2?
-RNAi was usedAny
for knockdown,
as opposed
gene
knockout,
of ash-2. product’ of ashsuggestions
for why to
the
‘possible
degradation
2 is mostdone
abundant
in the control P0 organisms? (See 3C)
Why was this experiment
this way?
-Firstly, because it is a viable method for gene suppression in culture and in vivo, and
the dropoff
in lifespan
increase
at F4ofrather
because synthetic dsRNAWhy
can selectively
& robustly
induce
suppression
specific
genes of interest.
than F5 as with wdr-5 and set-2?
-Secondly, because ash-2 deletion mutations have been shown ASH2 to be essential,
with its mutation resulting in embryonic lethality
Fig4
What do Fig4c,d show us?
What do Fig4a,b show us?
Other Longevity Regulators Effect
figure 5
H3K4me3 Expression between mutant and WT
figure 6
Some Statistics
Hierarchical Clustering - Genes with similar expression
patterns are grouped together and are connected by a
series of branches
Hypergeometric Probability - Drawing without
replacement in finite population size.
Principal component analysis - Charting a set of
observed variables into a set of linear uncorrelated
values.
figure 6
Possible Mechanisms for Epigenetic
Memory
Possible Mechanisms for Epigenetic
Memory
1. By H3K4me3 alone, loss of epigenetic memory due
to H3K4me3 itself expression threshold reached.
2. Other chromatin modifiers marks that are related to
H3K4me3.
3.Inherited non-coding RNA that eventually degrades
below functional level.
4. Other possible mechanisms? What do you think?
Evolution Perspective
Can this transgenerational effect of longevity
be interpreted as an adaptation?
Can you come up with a theory that fits the
results of the experiment?
Evolution Perspective
Consider H3K4me3 is conserved through
most organisms, does transgenerational
epigenetic memory, in terms of lifespan
alteration, apply to other species as well?
References
Xiao, Yu, Cecile Bedet, Valerie J Robert, Thomas Simonet, Steve Dunkelbarger, Cedric
Rakotomalala, Gwen Soete, Hendrik Korswagen, Susan Strome, and Francesca Palladino. 2011.
Caenorhabditis Elegans Chromatin-associated Proteins SET-2 and ASH-2 Are Differentially
Required for Histone H3 Lys 4 Methylation in Embryos and Adult Germ Cells. Proceedings of the
National Academy of Sciences of the United States of America. 108, no. 20: 8305-8310.
Greer, Eric, Travis Maures, Anna Hauswirth, Erin Green, Dena Leeman, Geraldine Maro, Shuo Han,
Max Banko, Or Gozani, Anne Brunet, and NATURE PUBLISHING GROUP. 2010. Members of the
H3K4 Trimethylation Complex Regulate Lifespan in a Germline-dependent Manner in C. Elegans.
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