Transcript Peromyscus polionotus (the monogamous mouse)

What did Herostratus do?
A. He designed the Colossus of Rhodes.
B. He financed the construction of the lighthouse
of Alexandria.
C. He burned the temple of Artemis.
D. He decorated the statue of Zeus at Olympia.
E. Dude, I don’t care what you say, Milla Jovovich
ROCKS. Can’t wait for “Resident Evil IV: the
Life of Dick Cheney”
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Image courtesy of Prof. Jay Hollick, MCB Department
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?!!!
R. Alexander Brink, 1950
Vicky Chandler, Jay Hollick et al
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What is going on?
1. The green maize plant is not outcrossing, it is
selfing.
2. The red allele is incompletely penetrant,
except when in a homozygous state.
3. This is actually two-locus inheritance, and the
green locus exhibits full dominant epistasis to
the red locus.
4. This is actually two-locus inheritance, and the
green locus exhibits full recessive epistasis to
the red locus.
5. Mmmmm … Milla …
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What IS going on
This is a phenomenon known as
“paramutation.”
It involves a change in gene behavior that is
not associated with a change in the DNA
sequence.
Hence, it is, strictly speaking, not in the
realm of genetics.
Thus, it is epigenetic.
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Broadly speaking
An “epigenetic” effect on the genome
changes the phenotype without changing
the genotype.
 The power of the environment and of life
history
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Technically
“A mitotically or meiotically heritable change
in gene expression state (or genome
functional state) that is not associated with
a change in the primary sequence of
DNA.”
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In other words
Genetics
Organism (or a cell)
with a phenotype
↓
Mutation (change in
DNA)
↓
Different phenotype
Epigenetics
Organism (or a cell)
with a phenotype
↓
Something happens,
but not a change in the
DNA
↓
Different phenotype
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“Cloning”:
hello, Dolly,
and
hello again, Dolly
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King and Briggs (1956).
Serial transplantation of embryonic nuclei
Cold Spring Harbor Symp. Quant. Biol. 21: 271-289.
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McKinnell, R. G. 1978. Cloning: Nuclear Transplantation in Amphibia.
University of Minnesota Press, Minneapolis.
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?
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How can one explain the fact that
cloning works so much better if
one use a cell from an early
embryo as the donor of the
nucleus?
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Two explanations
1. Alteration of the actual DNA of the cells
as the embryo develops.
2. Something else.
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Reya, Clarke, and Weissman. Nature 2001.
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Of the cells on the previous set of slides, which have
significant alterations in their DNA sequence relative to that
of the original zygote?
A.
B.
C.
D.
E.
The neuron.
The fibroblast.
The muscle cell.
The T cell.
The macrophage.
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King and Briggs (1956).
Serial transplantation of embryonic nuclei
Cold Spring Harbor Symp. Quant. Biol. 21: 271-289.
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Dolly
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Bill Ritchie
Ian Wilmut
Dolly
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Semantics
1. Reproductive cloning: make new
organisms.
2. Therapeutic cloning (aka “somatic cell
nuclear transfer”): no organism made.
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Extensive abnormalities in cloned
animals
•
•
•
•
Lung failure
Liver failure
Obesity
Etc etc
Two problems:
1. Cloning is incredibly inefficient.
2. Of the animals that are born, many have
severe defects.
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Proof that these abnormalities are
entirely epigenetic
Dolly’s lambs, and the
offspring of all cloned
animals, are normal.
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Solter and Surani
Gynogenetic embryos – very small.
Androgenetic embryos – very large.
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Ah, terminology
Genes for which you have your Mother’s
copy turned on:
Maternally expressed
Genes for which you have your Dad’s copy
turned on:
Paternally expressed
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What covalent posttranslational modification does genomic
DNA undergo during mammalian ontogeny?
A.
B.
C.
D.
E.
Phosphorylation
Methylation
Acetylation
All of the above
None of the above
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Spontaneous meCpG deamination (colon cancer)
Should be 4% of all NN – in
fact, is 0.8%.
Methylation:
C  5mC
CpG  5mCpG
5mCpG  TpG  TpA
deamination  MMR
CpG UpG  CpG
(no mutation)
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Pl is Changed to Pl’
“paramutation”!
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The Haig hypothesis
Imprinting evolved as a manifestation of
parental conflict over the allocation of
maternal resources to the developing
fetus: “intrauterine tug of war” over how
big the fetus will be.
Paternally expressed genes increase
embryo size.
Maternally expressed genes decrease
embryo size.
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Peromyscus polionotus
(the monogamous mouse)
Vrana et al. Nature Genetics 20: 362 (1998).
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Don’t clone humans
1. Responsibility for child and his/her
“developmental abnormalities.”
2. Naïve overestimation of role of DNA in
shaping the human being.
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“Therapeutic cloning”
= somatic cell nuclear transfer
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Embryonic stem cells
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Annu. Rev. Cell Dev. Biol. 2001. 17:435-462.
EMBRYO-DERIVED STEM CELLS: Of Mice and Men
Austin G. Smith
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ES cells – status quo
• Limited number of human ES cell lines
available for research with federal funds
• Growth on mouse feeders makes them
unsuitable for use as therapeutics
• The indications being considered are,
among others, cardiovascular and
neurological
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Why ES cells and not
adult stem cells?
For the simple reason that ES cells are
incomparably easier to grow to large
numbers in a dedifferentiated state, and
then drive them – in a controlled fashion! –
to differentiate into a specific cell type.
Note: in this context, “incomparably” means
“the difference between essentially
impossible and feasible.”
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“Dopamine neurons derived from embryonic stem cells
function in an animal model of Parkinson's disease” – Ron
McKay et al
Parkinson's disease is a widespread condition caused by the loss of
midbrain neurons that synthesize the neurotransmitter dopamine.
Cells derived from the fetal midbrain can modify the course of the
disease, but they are an inadequate source of dopaminesynthesizing neurons because their ability to generate these
neurons is unstable. In contrast, embryonic stem (ES) cells
proliferate extensively and can generate dopamine neurons. If ES
cells are to become the basis for cell therapies, we must develop
methods of enriching for the cell of interest and demonstrate that
these cells show functions that will assist in treating the disease.
Here we show that a highly enriched population of midbrain neural
stem cells can be derived from mouse ES cells. The dopamine
neurons generated by these stem cells show electrophysiological
and behavioural properties expected of neurons from the midbrain.
Our results encourage the use of ES cells in cell-replacement
therapy for Parkinson's disease.
Nature. 2002 Jul 4;418(6893):50-6
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The problem
In order to generate ES cells, one has to
destroy an early human embryo
• Twenty eight thousand IVF births in the US
in 1998
• Six to fourteen embryos per birth – healthy
ones frozen, and then discarded (=flushed
down a sink)
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Reading
Life's Dominion: An Argument about
Abortion, Euthanasia, and Individual
Freedom
Ronald Dworkin
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A way to overcome this entire issue?
1. Patient with failing organ.
2. Take nucleus from patient’s cell.
3. Do somatic cell nuclear transfer to
generate ES line from that patient.
4. Transdifferentiate that line ex vivo into
cell type relevant to disease.
5. Reimplant in patient.
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Correction of a Genetic Defect by
Nuclear Transplantation and
Combined Cell and Gene
Therapy
Rideout et al.
Cell (2002)
109, 17-27
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Pigmented
retinal epithelium
Neuroepithelial
rosset
http://www.nature.com/news/specials/hwang/index.html
Bone
Cartilage
Glandular
epithelium
with smooth
muscle
and connective
tissue
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What’s next with “therapeutic cloning”?
(“nuclear transfer”)
I don’t know.
There is likely to be a complex polemic
between patient advocacy groups (on the
one hand) and groups opposed to somatic
cell nuclear transfer on various grounds.
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Mice cloned from olfactory
sensory neurons
Eggan et al.
(Rudolf Jaenisch and Richard Axel)
Nature (2004)
428(6978):44-9
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Natalie Angier
Unnatural Obsessions
“The adjective that scientists use to describe
a well-wrought experiment is “elegant” –
which means not only that it worked, but it
worked in style.”
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Sense of smell
“One particularly clear example of neuronal diversity is
provided by the olfactory sensory epithelium. In the
mouse, each of the 2,000,000 cells in the olfactory
epithelium expresses only one of about 1,500 odorant
receptor genes, such that the functional identity of a
neuron is defined by the nature of the receptor it
expresses. Thus, the sensory epithelium consists of at
least 1,500 neuronal types. The pattern of receptor
expression is apparently random within one of four
zones in the epithelium, suggesting that the choice of
receptor gene may be stochastic. One mechanism to
permit the stochastic choice of a single receptor could
involve DNA rearrangements.”
Eggan et al. Nature. 2004 Mar 4;428(6978):44-9
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Allelic inactivation regulates
olfactory receptor gene expression
We suggest a model in which a hierarchy of
controls is exerted on the family of odorant
receptor genes to assure that a sensory neuron
expresses a single receptor from a family of
1000 genes. We propose that a cis-regulatory
element directs the stochastic expression of only
one gene from a large array of linked receptor
genes. Moreover, only one allelic array encoding
multiple receptor genes is active in an individual
neuron. We demonstrate that in a neuron
expressing a given receptor, expression derives
exclusively from one allele.
Chess et al. Cell. 1994 Sep 9;78(5):823-34
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Eggan et al. Nature. 2004 Mar 4;428(6978):44-9
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Eggan et al. Nature. 2004 Mar 4;428(6978):44-9
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Question  answer
“The regulation of gene expression by DNA
rearrangement is rare, but this mechanism has
nonetheless been suggested to explain the
diversity inherent in complex nervous systems.”
Well, we now know that it is NOT how neuronal
diversity in olfactory epithelium is created. The
difference between the individual neurons
expressing different receptors is not at the level
of DNA – it’s epigenetic.
Eggan et al. Nature. 2004 Mar 4;428(6978):44-9
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