Transcript lz(g)

“For difference determined by one
gene…”
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Five year survival rates, in %.
Cancer Site
Brain & Other Nervous
Breast (females)
Cervix Uteri
Colon & Rectum
Esophagus
Hodgkin's Disease
Kidney & Renal Pelvis
Larynx
Leukemias
Liver & Intrahep
Lung & Bronchus
Melanoma of Skin
Multiple Myeloma
Ovary
Pancreas
Prostate
Stomach
Testis
Thyroid
Urinary Bladder
All Sites
1974-76
22.3
74.3
68.5
49.5
4.7
71.1
51.3
65.4
34.2
3.8
12.3
79.7
24.4
36.5
2.6
66.7
15.1
78.6
91.9
72.4
49.3
1977-79
24.4
74.5
67.7
51.7
5.1
73
50.8
66.8
36.6
3.7
13.3
81.5
26.1
38.1
2.5
70.9
16.7
87.2
92.5
74.8
49.8
1980-82
25
76.2
66.9
54.2
6.7
74.3
51.4
68
37.4
3.4
13.3
82.1
28
38.9
3.1
73.1
17.5
91.7
94.2
77.9
50.6
http://seer.cancer.gov/publications/raterisk/rates28.html
1983-90
27.3
80.4
67.4
59.2
9.2
78.9
56.3
67
38.3
6
13.4
85.1
27.7
41.8
3.2
79.6
18.5
93.3
94.6
79.8
53.9
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Hanahan and Weinberg (2000) Cell 100: 57–70.
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Hanahan and Weinberg (2000) Cell 100: 57–70.
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A Russian proverb that aptly describes most
current cancer treatment modalities
«Лучшее средство от кровотечения из носа –
жгут на шею».
“The best cure for a nosebleed is a torniquet on
the neck.”
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“Chemo” drugs
Depolymerization of microtubules
Intrastrand DNA crosslinking
Cell cycle arrest
Apoptosis (programmed cell death)
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“Malignancy of somatic cell hybrids”
B. Ephrussi et al., Nature (1969) 224:1314
The studies of Ephrussi et al. and Harris provided compelling evidence that
the ability of cells to form a tumor is a recessive trait. They observed that the
growth of murine tumor cells in syngeneic animals could be suppressed when
the malignant cells were fused to nonmalignant cells, although reversion to
tumorigenicity often occurred when the hybrids were propagated for extended
periods in culture. The reappearance of malignancy was found to be associated
with chromosome losses. Stanbridge and his colleagues studied hybrids made
by fusing human tumor cell lines to normal, diploid human fibroblasts. Their
analysis confirmed that hybrids retaining both sets of parental chromosomes
were suppressed, with tumorigenic variants arising only rarely after
chromosome losses in the hybrids. Moreover, it was demonstrated that the loss
of specific chromosomes, and not simply chromosome loss in general,
correlated with the reversion to tumorigenicity.
The observation that the loss of specific chromosomes was associated with
the reversion to malignancy suggested that a single chromosome (and perhaps
even a single gene) might be sufficient to suppress tumorigenicity. To directly
test this hypothesis, single chromosomes were transferred from normal cells to
tumor cells, using the technique of microcell-mediated chromosome transfer. It
was found that the transfer of a single chromosome 11 into the HeLa cervical
carcinoma cell line suppressed the tumorigenic phenotype of the cells. Many
studies have now demonstrated that transfer of even very small chromosome
fragments will specifically suppress the tumorigenic properties of certain cancer
cell lines.
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Ventura et al Nature 445: 661
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Xue et al Nature 445: 656
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Martins et al Cell 127: 1323
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Why does restoration of p53
function lead to tumor
regression?
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Hanahan and Weinberg (2000) Cell 100: 57–70.
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Epistasis
(or: an epistatic interaction between two loci)
1. Pick a trait.
2. Find a mutant  phenotype #1
3. Find a different mutant  different phenotype
(#2)
4. Cross the two mutants: get not a mix of
phenotypes, but instead, either phenotype #1
or #2.
The term “epistasis” refers to a phenomenon in
which an allele of one gene masks (“stops”)
the effects on the phenotype of an allele of a
different gene.
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How can one tell, if two
organisms under study that
exhibit mutant phenotypes for a
particular trait have a mutation in
different genes
or in the same gene?
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Complementation test
“Complementation is the production of a
wild-type phenotype when two haploid
genomes bearing different recessive
mutations are united in the same cell.”
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The cis-trans test
(aka complementation test)
Edward Lewis
(NP 1995)
Are two different recessive mutations that appear to affect the same trait
in the SAME gene or in DIFFERENT genes?
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Orgo
cis-2-butene
trans-2-butene
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The cis-trans test, 1949:
lozenge (M. Greene)
Two different recessive mutants, both with the same
phenotype (small eyes and fused facets).
Are they mutations in the same gene?
Make two different fly lines and compare their phenotypes.
Cis:
Trans:
wt
wt
wt
lz(g)
lz(BS)
lz(g)
lz(BS)
wt
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Cis:
Trans:
wt
wt
wt
lz(g)
lz(BS)
lz(g)
lz(BS)
wt
This is a control experiment.
The flies will be wild-type
regardless of whether
BS and g are in the
same gene or not.
If flies are normal, then
mutations are in different genes.
If the phenotype is still mutant,
then BS and g must be in the
same gene!!!
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Gene A
Gene B
wt
lz(g)
lz(BS)
wt
Aa
Bb
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Baur et al. Nature 444: 337.
Lagouge et al. Cell 127: 1109.
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Rine schematic
mate to a cells
Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.
Fig. 17.14
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The data
• Colonies screened: 675,000
• Colonies that mated to a: 295
• Major complementation groups: 4
silent information regulators:
SIR1, SIR2, SIR3, SIR4
Jasper Rine and Ira Herskowitz (1987) Genetics 116: 9-22.
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Xeroderma pigmentosum
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What was actually done
1.
By linkage analysis, it was discovered that the same
disease (XP) can be caused by mutations in 7 distinct
loci.
2. The cDNA from each gene was cloned.
3. An assay was developed to measure, how sensitive to
UV light cells are.
4. Experiment: take cells from patient type A, and
introduce each of the 7 cDNAs, one after another.
5. Whichever cDNA restores the wild-type phenotype
corresponds to the gene that is mutated in that cell.
 Bin XP mutations into “complementation groups”!
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Wait a minute
Ahem.
Fine. You take a cell that’s mutant, stick in a gene,
the cell is now wild-type, and you tell us this
means the gene you stuck in is the gene that is
mutated in the cell.
What if the cell has a mutation in a completely
different gene, and the gene you stuck in is just
epistatic to the first one?!
Good question.
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Auf Wiedersehen (with respect to
phenotype), Herr Mendel
Gene interactions in the
establishment of phenotype
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For complete clarity
1. All genotypes – except in cases of
nondisjunction – follow Mendel’s first law, and
– except in cases of linked genes < 50 cM
away from each other – Mendel’s second law.
2. With the exception of human genetic disease,
which is, let’s face it, very rare, and things like
blood group inheritance, which belongs mostly
on the MCAT (note – its inheritance, not blood
groups themselves), the inheritance of
phenotype seldom follows Mendel’s laws.
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http://www.gmi.oeaw.ac.at/
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“… the stadium capacity is now
officially listed as 75,662”
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Steinberg Curr Opin Hematol 13: 131
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“An SCN9A channelopathy causes
congenital inability to experience pain”
Nature Dec. 14, 2006
“The index case for the
present study was a tenyear-old child, well known to
the medical service after
regularly performing 'street
theatre'. He placed knives
through his arms and
walked on burning coals,
but experienced no pain. He
died before being seen on
his fourteenth birthday, after
jumping off a house roof.”
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So – let’s think about this
The small fraction of African-Americans who are
relatively pain-free …
… could they be heterozygous for a loss-offunction mutation in SCN9A?
In other words, could this be recessive epistasis?
If yes, could this suggest that a small-molecule
inhibitor of that specific pain receptor could be a
more effective analgesic for SCA patients than
God-awful parenteral morphine!
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Strict definition
Epistasis is revealed in modified Mendelian
ratios in dihybrid crosses.
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Recessive epistasis
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Dominant epistasis
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Future e-mail
Professor,
Thanks for nothing, BUSTER.
First you tell us that modified Mendelian
ratios can occur in monohybrid crosses
(e.g., in a dominance series), then you tell
us they occur in dihybrid crosses and are,
in fact, a hallmark of epistasis.
How can one tell the difference?
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Genetics of continuous
variation
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Yao Ming, 7’6’’
Michael Jordan, 6’6’’
Muggsy Bogues,
5’3’’
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In a population, phenotypes of
individuals for a quantitative trait
tend to be normally distributed
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The Great Schism (1901-1935)
“Naturalists”
• the origin and
meaning of diversity
• populations, groups,
higher taxa
• gradualism
• ultimate causation
“The Mendelians”
• transformation of
genes
• individual genes/loci
• saltationism
• no “why” questions
“Only the experimental method would permit an objective discussion of
the theory of evolution, in striking contrast to the older speculative
method of treating evolution as a problem of history.” (T.H. Morgan)
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Synthesis: Population Genetics
•
•
H. Nilsson-Ehle, R.A. Fisher, J.B.S.
Haldane, S. Wright: continuous
phenotypic variation is not at odds with
particulate inheritance:
multiple loci + epistasis
S.S. Chetverikov: naturally occurring
recessives as food for natural selection.
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Morgan, ch. 8
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Hermann Nilsson-Ehle
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Central limit theorem
Carl Friedrich Gauss 
If a variable is the sum of many independent
variables, then its distribution will be normal:
e
x
2
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“Additive effects of genes”
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Next time:
why are all calico cats female? –
and a related question:
why is metastatic prostate cancer
almost always incurably lethal?
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