Post on 02-Jan-2016
description
transcript
Gene sequence is inherited (you’re stuck with what you have)
However:Gene expression is influenced by inheritance AND age, tissue type, physical environment and social environment
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atgtcagccgataactgactgatcgtaaattgagtttt
protein
messenger RNA(mRNA)
“gene expression” = mRNA abundance
gene
gene
Variation in gene sequence (DNA polymorphisms) can be found by “gene mapping” and DNA sequencing
Variation in gene expression can be found using “microarrays”
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atgtcagccgataactgactgatcgtaaattgagtttt
protein
messenger RNA(mRNA)
“gene expression” = mRNA abundance
gene
atgtcagccgataactgactgatggtaaattgagtttt
DNA polymorphism
Microarrays measure mRNA abundance for 1000s of genes simultaneously
Behavioral division of labor in the honey bee colony
10 20 30 40
% old foragers in colony
10
20
30
40
50
% i
ntr
od
uce
d b
ees
that
in
itia
ted
fo
rag
ing
by
day
14
Age at onset of foraging is socially regulated
Behavioral division of labor in the honey bee colony
Age at onset of foraging is socially regulated
Inhibitory social pheromone
Nurse Forager
Behavioral division of labor in the honey bee colony
Age at onset of foraging is also genetically variable
m lc
m
m lc
c
m lc
l
Introduced bees
Host colony
% o
f in
tro
du
ced
bee
s fo
rag
ing
at
15 d
ays
of
age
60
40
20
0
m, c and l are different genetic strains
Each pair of spots is a “detector” for mRNA abundance for 1 bee gene.
We can analyze mRNA abundance for ~5500 different genes at the same time (in a single dissected bee brain)
Honey bee brain microarray
Comparing gene expression in a nurse brain vs. a forager brain
Nurse mRNA level
Fo
rag
er m
RN
A l
evel
Dissectednurse brain
microarray hybridization
Dissectedforager brain
labeling reaction
Do age-related changes in behavior involve changes in gene expression in the brain?
~700 one-day-old bees(marked)
“Typical” host colonies(ca. 40,000 mixed-age bees)
Collect marked bees
day 7 day 30
Youngnurses(n = 18)
Old foragers(n = 18)
YN OF
Gen
es
Bee brains
Yellow = high mRNA abundance
Blue = low mRNA abundance
YN = young nurseOF = old forager
About 1/3 of genes expressed in the bee brain show differences in expression!
But…Are gene expression differences really associated with behavior differences or with age?
YN OF
Gen
es
Bee brains
Yellow = high mRNA abundance
Blue = low mRNA abundance
YN = young nurseOF = old forager
About 1/3 of genes expressed in the bee brain show differences in expression!
Changing age-demography in the colony (i.e., social environment) allows us to collect “precocious” young forgers and “over-aged” old nurses
~1500 one-day-old bees(marked)
All bees are same age!!!
Collect marked bees
day 7 day 30
Youngnurses(n = 6)
Old nurses(n = 6)
Youngforagers(n = 6)
Old foragers(n = 6)
YN OF YN ONYF OF
Gen
es
Bee brains
Yellow = high mRNA abundance
Blue = low mRNA abundance
YN = young nurseYF = young foragerON = old nurseOF = old forager
Gene expression was primarily associated with behavior, not age!
YN OF YN ONYF OF
Gen
es
Bee brains
Yellow = high mRNA abundance
Blue = low mRNA abundance
YN = young nurseYF = young foragerON = old nurseOF = old forager
>21.5
1.251
0.80.67<0.5
Although 1/3 genes show differences, only ~50 genes are needed to “predict” whether a bee is a nurse or a forager(Whitfield, Cziko & Robinson. Science 2003, 302: 296)
Y = young (7 ±2 days)O = old (30 ±2 days)N = NurseF = Forager
Typical colonybees
Single-cohort (age-matched)
bees
mR
NA
le
vel
Is gene expression in the brain a cause or consequence of behavior?
Brain gene expression• Upstream regulation of behavior
Behavior
Brain gene expression• Consequence of behavioral activity, experience or environmental differences
?
?Behavior
-- or --
Is gene expression in the brain a cause or consequence of behavior?
Manipulate gene expression in brain
Effects on behavior?
Direct test of causation:
Is gene expression in the brain a cause or consequence of behavior?
Direct test of causation:
Manipulate gene expression in brain
Effects on behavior?
Can’t do th
is yet –
need transgenics!!!
Is gene expression in the brain a cause or consequence of behavior?
Brain gene expression• Upstream regulation of behavior
Behavior
Brain gene expression• Consequence of behavioral activity, experience or environmental differences
?
?Behavior
-- or --
Brain gene expression in the absence of task-related experience
Caged bees(no task-related
experiences)
Brain gene expression in the absence of task-related experience
Social cue or treatment that
accelerates the onset of foraging
Forager-like changes in brain gene expression?
Caged bees(no task-related
experiences)
Brain gene expression in the absence of task-related experience
Social cue or treatment that
accelerates the onset of foraging
Social cue or treatment that delays the onset of foraging
Forager-like changes in brain gene expression?
Nurse-like changes in brain gene expression?
Caged bees(no task-related
experiences)
High in foragers
(32)
High in nurses
(18)
Induced by methoprene
(249)13 0
Repressed by methoprene
(222)0 11
Treat with methoprene(JH analog)
Caged bees(no task-related
experiences)
Juvenile hormone analog (methoprene) accelerates the onset of foraging and causes forager-like changes in brain gene expression (in the absence of experience)
“marker” genes
Whitfield CW et al. PNAS. 2006. Oct 31; 103(44):16068-75.
Caged bees(no task-related
experiences)
Treat with QMP
High in foragers
(32)
High in nurses
(18)
Induced by QMP (602)
0 4
Repressed by QMP (704)
18 2
Queen mandibular pheromone (QMP) delays the onset of foraging and causes nurse-like changes in brain gene expression (in the absence of experience)
“marker” genes
Grozinger CM, Sharabash NM, Whitfield CW, Robinson GE. PNAS. 2003. Nov 25; 100:14519
Nurse
Comb-b
uilder
GuardUnderta
ker
(corp
se-rem
over)
Forager
Many behaviors… but how many involve gene expression differences?
> 21.5
1.251
0.80.67< 0.5
Gen
e cl
ust
ers
(exp
ress
ion
lev
el i
n b
rain
)
Are gene expression changes robust at the level of individual?
Can gene expression profile in an individual bee’s brain be used to correctly predict behavioral group?
Method:
1. Computer identifies a set of “predictor genes” for behavior using expression data from the 59 bees in the “training set.”
2. Computer attempts to classify the single “test” bee based on its expression of the predictor genes.
3. Repeat iteratively for all 60 individual bees.
Result:
Computer can correctly assign behavior group for 57 out of the 60 bees.
“Training set”59 bees
(computer knows behavior)1 bee
(computer attempts to
classify)
“Leave-one-out” cross-validated class prediction
“Test set”
nurse or forager?