Download Selector genes determine segment identity

2/15/2008
Figure 5.2
Selector genes determine
segment identity
Combination of
gap gene and pairrule gene
expression
patterns define the
selector gene
expression pattern
Box 4A: 3’--> 5’ organization reflects anterior--->
posterior expression
Figure 2.44: selector genes are arranged in two complexes
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2/15/2008
Box4A
Drosophila
Vs.
Mouse
Figure 2.45
Mutations in selector genes
result in homeotic
transformations - one body
part is transformed into
another
Vs.
Caenorhabditis elegans
Figure 5-12
Figure 2.45
Bithorax mutant - anterior
compartment of haltere
transformed into anterior
wing compartment
Postbithorax transformation of posterior
compartment
The dominant Antennapedia
mutation causes legs to
develop in place of antenna
((gain-of-function
i ff
i - gene is
i
expressed ectopically in the
head as well as the thorax
recessive mutation - (loss-offunction)) ggene is not
expressed in thorax, antenna
are formed in place of legs
Double mutant = four wings
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Initial expression of the
gap gene Krüppel predicts
later expression of selector
gene Antennapedia
Box 4A: 3’--> 5’ organization reflects anterior--->
posterior expression
Figure 2.46
Expression of the 3 genes
in the bithorax complex
d fi
defines
parasegment
identity
Ubx gene
has a
number of
regulatory
regions
that control
expression
in a
particular
region
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If delete all 3 genes of
the bithorax compex,
all segments
g
transformed to
segment 4
If add Ubx back, get 4,
5 and 6…
•Ubx specifies
parasegments 5 and
6
Figure 2.46
If Ab-A is also restored,
identity of parasegments 7
and 8 is restored (all
remaining like parasegment
9)
Figure 2.46
Expression of selector
genes defines
parasegment identity
If Ab-A and Ab-B are restored,
identity of all parasegments
except 5 and 6 are restored
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2/15/2008
Expression of anterior homeotic genes is
repressed by posterior homeotic genes
Chromatin remodeling maintains selector
gene expression in absence of gap genes
“posterior dominance”
Polycomb - maintains repression
Trithorax - maintains activation
Establishing A/P
axis
Defining regions
more precisely
Defining parasegments and
their orientation
Defining segment
identity
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