Table Of ContentAus
dem
Adolf-‐Butenandt-‐Institut
Lehrstuhl
Physiologische
Chemie
der
Ludwig-‐Maximilians-‐Universität
München
Vorstand:
Prof.
Dr.
Andreas
Ladurner
Cell-‐type-‐specific
approaches
for
dissecting
gene
activity
and
chromatin
structure
within
the
Drosophila
head
Dissertation
zum
Erwerb
des
Doktorgrades
der
Naturwissenschaften
an
der
Medizinischen
Fakultät
der
Ludwig-‐Maximilians-‐Universität
vorgelegt
von
Tamás
Schauer
aus
Mohács
(Ungarn)
2013
Gedruckt
mit
Genehmigung
der
Medizinischen
Fakultät
der
Ludwig-‐Maximilians-‐Universität
München
Betreuer:
Prof.
Dr.
Andreas
Ladurner
Zweitgutachter:
Prof.
Dr.
Ralph
A.W.
Rupp
Dekan:
Prof.
Dr.
med.
Dr.
h.c.
M.
Reiser,
FACR,
FRCR
Tag
der
mündlichen
Prüfung:
01.08.2014
2
Eidesstattliche
Versicherung
Schauer,
Tamás
Ich
erkläre
hiermit
an
Eides
statt,
dass
ich
die
vorliegende
Dissertation
mit
dem
Thema
"Cell-‐type-‐specific
approaches
for
dissecting
gene
activity
and
chromatin
structure
within
the
Drosophila
head"
selbständig
verfasst,
mich
außer
der
angegebenen
keiner
weiteren
Hilfsmittel
bedient
und
alle
Erkenntnisse,
die
aus
dem
Schrifttum
ganz
oder
annähernd
übernommen
sind,
als
solche
kenntlich
gemacht
und
nach
ihrer
Herkunft
unter
Bezeichnung
der
Fundstelle
einzeln
nachgewiesen
habe.
Ich
erkläre
des
Weiteren,
dass
die
hier
vorgelegte
Dissertation
nicht
in
gleicher
oder
in
ähnlicher
Form
bei
einer
anderen
Stelle
zur
Erlangung
eines
akademischen
Grades
eingereicht
wurde.
Ort,
Datum
Unterschrift
Doktorand
3
Acknowledgements
Foremost
I
would
like
to
thank
Prof.
Dr.
Andreas
Ladurner
for
giving
me
the
opportunity
to
work
on
my
PhD
project
in
his
group
at
EMBL
and
in
his
department
at
LMU.
It
would
have
been
impossible
to
start,
manage
and
finish
my
PhD
work
without
his
guidance
and
support.
I
am
especially
grateful
to
Dr.
Carla
Margulies
for
the
successful
co-‐work,
the
motivating
discussions
and
the
useful
feedback
that
helped
the
progress
of
my
PhD
project.
Thank
you
for
the
scientific
and
non-‐scientific
input,
the
active
co-‐writing
of
our
papers
and
the
careful
reading
of
my
thesis
manuscript.
My
special
thanks
go
to
Dr.
Petra
Schwalie
for
the
fruitful
collaboration
and
discussions.
Thank
you
for
your
enthusiastic
work
in
analyzing
my
data
what
was
crucial
to
write
this
manuscript.
I
wish
to
acknowledge
Sandra
Esser
at
LMU
and
Bianca
Nijmejer
at
EMBL
for
the
technical
support.
I
am
also
grateful
to
Dr.
Anton
Eberharter
and
Dr.
Corey
Laverty
for
all
the
scientific
and
management-‐related
help
including
reading
this
thesis.
I
also
would
to
thank
all
members
of
the
Ladurner
group/department
and
Margulies
group,
especially
Ava
Handley
for
the
discussions
and
helping
each
others´
work
as
well
as
Dr.
Gyula
Timinszky
and
Dr.
Markus
Hassler
for
the
scientific
advices.
At
last
but
not
at
least
I
thank
my
family,
my
parents,
my
friends
in
Hungary
and
in
Germany
as
well
as
my
life
partner
for
supporting
and
motivating
me
in
good
and
bad
times.
4
Table
of
Contents
Table
of
Contents
1
SUMMARY
................................................................................................................
7
1.1
Summary
(in
English)
.....................................................................................................................................
7
1.2
Zusammenfassung
...........................................................................................................................................
9
2
INTRODUCTION
.....................................................................................................
13
2.1
Epigenetic
landscape
of
development
...................................................................................................
14
2.1.1
Development
of
major
cell-‐lineages
in
Drosophila
.............................................................................
15
2.1.2
Cell
types
of
the
fly
head
.....................................................................................................................................
17
2.1.3
Gene
regulatory
networks
.................................................................................................................................
23
2.2
Regulation
of
gene
expression
.................................................................................................................
25
2.2.1
RNA
polymerase
II-‐mediated
transcription
............................................................................................
26
2.2.2
Chromatin
structure
and
function
................................................................................................................
29
2.2.3
Post-‐transcriptional
regulation
.....................................................................................................................
38
2.3
Cell-‐type-‐specific
approaches
to
dissect
gene
activity
.....................................................................
41
2.3.1
General
workflow
...................................................................................................................................................
41
2.3.2
Chromatin
mapping-‐based
methods
...........................................................................................................
44
2.3.3
RNA
profiling-‐based
methods
.........................................................................................................................
46
2.3.4
Data
analysis
.............................................................................................................................................................
50
2.3.5
Validation
of
cell
type
specificity
...................................................................................................................
50
2.3.6
Perspectives
...............................................................................................................................................................
52
2.4
Aims
of
the
thesis
..........................................................................................................................................
53
3
CAST-‐CHIP
–
CHROMATIN
AFFINITY
PURIFICATION
FROM
SPECIFIC
CELL
TYPES
........
54
3.1
Summary
..........................................................................................................................................................
54
3.2
Introduction
....................................................................................................................................................
55
3.3
Methods
............................................................................................................................................................
56
3.3.1
Experimental
procedures
..................................................................................................................................
56
3.3.2
Data
analysis
.............................................................................................................................................................
58
3.4
Results
..............................................................................................................................................................
60
3.4.1
Cell-‐type-‐specific
gene
activity
maps
using
CAST-‐ChIP
....................................................................
60
3.4.2
Validation
of
CAST-‐ChIP
......................................................................................................................................
67
3.5
Discussion
.......................................................................................................................................................
74
4
H2A.Z
–
AN
EPIGENETIC
MARK
FOR
UBIQUITOUS
GENE
ACTIVITY
.............................
76
4.1
Summary
..........................................................................................................................................................
76
4.2
Introduction
....................................................................................................................................................
77
4.3
Methods
............................................................................................................................................................
78
5
Table
of
Contents
4.3.1
Experimental
procedures
..................................................................................................................................
78
4.3.2
Data
analysis
.............................................................................................................................................................
79
4.4
Results
..............................................................................................................................................................
82
4.4.1
H2A.Z
is
an
active
mark
in
differentiated
cell
types
of
the
fly
CNS
............................................
82
4.4.2
H2A.Z
associates
with
chromatin
domains
that
display
ubiquitous
gene
expression
...
94
4.5
Discussion
.......................................................................................................................................................
98
5
TRAP
–
TRANSLATING
RIBOSOME
AFFINITY
PURIFICATION
FOR
CELL-‐TYPE-‐SPECIFIC
TRANSLATOME
PROFILING
........................................................................................
101
5.1
Summary
........................................................................................................................................................
101
5.2
Introduction
..................................................................................................................................................
102
5.3
Methods
..........................................................................................................................................................
103
5.3.1
Experimental
procedures
...............................................................................................................................
103
5.3.2
Data
analysis
..........................................................................................................................................................
105
5.4
Results
............................................................................................................................................................
107
5.4.1
Establishing
TRAP
in
Drosophila
................................................................................................................
107
5.4.2
Genome-‐wide
TRAP
profiling
.......................................................................................................................
115
5.5
Discussion
.....................................................................................................................................................
128
6
DISCUSSION
............................................................................................................
131
6.1
CAST-‐ChIP,
a
tool
for
cell-‐type-‐specific
chromatin
mapping
.......................................................
132
6.2
Ubiquitous
genes,
are
they
special?
......................................................................................................
134
6.3
TRAP,
profiling
mRNA
from
cell
types
.................................................................................................
137
6.4
Perspective
....................................................................................................................................................
138
7
LIST
OF
FIGURES
AND
TABLES
.................................................................................
141
8
ABBREVIATIONS
.....................................................................................................
143
9
APPENDIX
...............................................................................................................
144
9.1
CAST-‐ChIP
protocol
....................................................................................................................................
144
9.1.1
Chromatin
preparation
....................................................................................................................................
144
9.1.2
Chromatin
Immunoprecipitation
...............................................................................................................
146
9.2
TRAP
protocol
..............................................................................................................................................
147
9.2.1
TRAP
procedure
...................................................................................................................................................
147
10
BIBLIOGRAPHY
.....................................................................................................
150
6
Summary
1
Summary
1.1
Summary
(in
English)
Multicellular
organisms
develop
from
a
single
cell
(the
zygote)
and
each
cell
type
inherits
the
same
genetic
material
from
the
zygote.
Adult
organisms
are
composed
of
terminally
differentiated
cell
populations
that
carry
the
same
genome
but
differential
epigenomes.
The
epigenome
consists
of
modifications
or
marks
of
the
genome
that
determine
which
genes
are
activated
or
repressed.
The
differential
activity
of
genes
in
distinct
cells
maintains
their
phenotype,
identity
and
function.
However,
there
have
been
few
tools
available
until
recently
that
would
allow
us
to
profile
gene
activity
at
the
level
of
specific
cell
types.
The
lack
of
easily
applicable,
efficient
cell-‐type-‐specific
tools
prompted
me
to
develop
novel
biochemical
methods
and
to
refine
existing
protocols
for
profiling
transcription,
chromatin
and
mRNA
levels
genome-‐wide.
I
used
cephalic
(head)
cell
types
of
the
adult
fruit
fly
(Drosophila
melanogaster)
as
a
model
system
to
study
differential
gene
activity
in
differentiated
cell
types
including
neurons,
glia
and
the
fat
body
(adipocytes).
First,
I
developed
a
biochemical
method,
CAST-‐ChIP
(Chromatin
Affinity
Purification
from
Specific
cell
Types),
a
combination
of
the
UAS/Gal4
expression
system
and
the
affinity
purification
of
tagged
chromatin-‐bound
reporters.
To
study
transcription
in
distinct
cell
types,
I
expressed
a
tagged
subunit
of
the
RNA
polymerase
II
complex
in
the
cell
type
of
interest
and
used
the
tag
to
generate
cell-‐type-‐specific,
genome-‐wide
ChIP
profiles.
RNA
polymerase
II
marks
about
1500
genes
unique
to
neurons
or
glia.
Genes
identified
as
neuronal
share
characteristic
cellular
function
such
as
axon
guidance
of
neurons
and
are
expressed
in
other
neuronal
tissues,
such
as
the
larval
central
nervous
system.
Furthermore,
I
demonstrated
that
genomic
regions
marked
by
cell-‐type-‐specific
RNA
polymerase
II
show
GFP-‐reporter
activity
localized
within
the
labeled
cell
populations.
This
incidates
that
RNA
polymerase
II
profiling
is
a
suitable
tool
to
distinguish
gene
activity
in
different
cell
types.
Second,
I
applied
CAST-‐ChIP
to
study
chromatin
structure
of
cell
types
by
profiling
the
incorporation
of
the
active
histone
variant
(H2A.Z),
as
a
proof-‐of-‐principle
7
Summary
to
study
differences
in
chromatin
structure
between
unrelated
cell
types.
I
found
H2A.Z
present
at
expressed
genes
and
absent
from
inactive
genes,
as
shown
previously.
However,
H2A.Z-‐enriched
regions
do
not
completely
overlap
with
RNA
polymerase
II
regions.
Interestingly,
RNA
polymerase
II-‐bound
genes
lacking
H2A.Z
differ
the
most
in
their
expression
among
dissected
tissues.
Therefore,
I
hypothesized
that
H2A.Z
labels
genes
that
are
expressed
in
a
cell-‐type-‐independent
manner.
To
test
this,
I
used
CAST-‐
ChIP
to
compare
the
cell-‐type-‐specific
incorporation
of
H2A.Z.
Surprisingly,
H2A.Z
profiles
are
remarkably
similar
in
neurons
and
glia,
with
only
about
hundred
significant
differences.
In
addition,
H2A.Z
is
present
at
those
regions
which
share
RNA
polymerase
II
in
both
cell
types
and
is
absent
from
cell-‐type-‐specific
regions.
ChIP
analysis
of
the
fat
body,
which
is
another
head
cell
type
with
a
different
developmental
origin,
led
to
the
same
results.
To
validate
these
findings
by
comparing
distinct
developmental
stages,
I
found
only
a
few
H2A.Z
and
thousands
of
RNA
polymerase
II
regions
that
differ
between
the
embryo
and
adult
head
tissues.
Thus,
CAST-‐ChIP
revealed
a
novel
function
of
H2A.Z
in
marking
genes
with
ubiquitous,
cell-‐type-‐invariant
expression.
Using
this
approach,
I
could
distinguish
between
ubiquitous
(house-‐keeping)
and
specifically
regulated
genes.
Together
with
analyses
conducted
by
other
groups,
I
found
that
ubiquitous
genes
share
common
regulatory
features
including
promoter
structure
and
gene
length,
and
they
form
clusters
marked
by
insulator
binding
proteins.
Third,
I
refined
a
fly
RNA
profiling
approach
(TRAP:
Translating
Ribosome
Affinity
Purification),
first
developed
for
the
mouse,
to
obtain
information
about
cell-‐
type-‐specific
post-‐transcriptional
processes
that
regulate
cellular
function
downstream
to
transcription.
TRAP
measures
the
ribosome-‐bound
fraction
of
RNA
and
therefore
identifies
genes
that
are
not
only
transcribed
but
also
translated
(translatome).
The
dynamic
range
of
TRAP
was
greater
compared
to
the
previous
ChIP-‐based
methods
and
I
identified
twice
as
many
transcripts
as
RNA
polymerase
II-‐bound
genes
using
CAST-‐
ChIP,
indicating
the
greater
resolution
of
the
ribosome-‐tagging
method.
Using
TRAP
I
uncovered
transcripts
carrying
relevant
neuronal
functions
that
were
hidden
in
the
CAST-‐ChIP
data
lacking
RNA
polymerase
II
peaks.
Several
studies
revealed
that
mild
stress
conditions
induce
changes
only
on
the
translational
level;
therefore,
TRAP
is
a
suitable
tool
to
study
such
responses
in
various
cell
types.
In
summary,
in
my
PhD
thesis
I
present
and
compare
cell-‐type-‐specific
methods
to
profile
gene
activity
in
Drosophila
differentiated
cells.
I
developed
a
novel
method
8
Summary
(CAST-‐ChIP)
and
applied
an
existing
method
(TRAP)
to
map
1)
transcription
using
RNA
polymerase
II
CAST-‐ChIP;
2)
chromatin
structure
using
H2A.Z
CAST-‐ChIP
and
3)
the
translatome
of
ribosome-‐bound
mRNA
using
TRAP.
My
results
give
useful,
novel
information
for
the
scientific
community:
1)
the
cell-‐type-‐specific
profiles
serve
as
a
compendium
of
genes
involved
in
the
maintenance
of
cell
identity
and
function;
2)
using
these
approaches,
I
discovered
a
novel
function
of
H2A.Z
marking
ubiquitous/
housekeeping
genes,
highlighting
the
differential
regulation
of
cell-‐type-‐specific
genes;
3)
ChIP
profiling
does
not
identify
all
differences
among
cell
types
and
therefore
post-‐
transcriptional
profiling
has
to
be
involved
in
the
analysis.
Cell-‐type-‐specific
approaches
presented
in
this
thesis
are
promising
tools
that
will
allow
us
to
describe
cellular
responses
upon
environmental
perturbation,
identifying
differential
responses
to
environmental
change
in
distinct
cell
populations.
1.2
Zusammenfassung
Mehrzellige
Organismen
entwickeln
sich
aus
einer
einzigen
Zelle
(der
Zygote)
und
jede
Zelle
erbt
das
gleiche
genetische
Material
aus
der
Zygote.
Die
adulten
Organismen
sind
aus
terminal
differenzierten
Zellpopulationen
zusammengesetzt,
die
das
gleiche
Genom,
aber
unterschiedliche
Epigenome
tragen.
Das
Epigenom
besteht
aus
Modifikationen
oder
Markierungen
des
Genoms.
Diese
bestimmen,
welche
Gene
aktiviert
oder
reprimiert
werden.
Die
unterschiedliche
Aktivität
von
Genen
in
unterschiedlichen
Zellen
erhält
deren
Phänotyp,
Identität
und
Funktion
aufrecht.
Der
Mangel
an
leicht
anwendbaren
und
effizienten
Zelltyp-‐spezifischen
Werkzeugen
hat
mich
dazu
veranlasst,
neuartige
biochemische
Methoden
zu
entwickeln
und
bestehende
Protokolle
zu
verfeinern.
Dadurch
kann
die
Transkription,
die
Chromatinstruktur
und
die
Menge
an
mRNA
Zelltyp-‐spezifisch,
genomweit
profiliert
werden.
Ich
benutzte
Zellen
vom
Kopf
der
adulten
Fruchtfliege
(Drosophila
melanogaster)
als
Modellsystem
um
die
Genaktivität
der
differenzierten
Zelltypen
wie
Neuronen,
Glia
und
Fettzellen
zu
untersuchen.
Zuerst
entwickelte
ich
ein
biochemisches
Verfahren,
CAST-‐ChIP
(Chromatin
Affinitätsreinigung
von
spezifischen
Zelltypen)
genannt,
welches
eine
Kombination
aus
dem
UAS/Gal4
Expressionssystem
und
aus
einer
Affinitätsreinigung
von
einem
9
Summary
markierten
Chromatin-‐gebundenen
Reporter
darstellt.
Um
die
Transkription
in
verschiedenen
Zelltypen
zu
untersuchen,
exprimierte
ich
eine
markierte
Untereinheit
des
RNA
Polymerase
II
Komplex
im
Zelltyp
von
Interesse
und
erzeugte
Zelltyp-‐
spezifische,
genomweite
ChIP
Profile.
RNA-‐Polymerase
II
markiert
etwa
1500
Gene
spezifisch
für
Neuronen
oder
Gliazellen.
Gene,
die
als
Neuron-‐spezifisch
identifiziert
wurden,
haben
charakteristische
zelluläre
Funktionen,
wie
zum
Beispiel
die
Axon
Führung
von
Neuronen.
Sie
werden
auch
in
anderen
neuronalen
Geweben
sowie
im
larvalen
Zentralnervensystem
exprimiert.
Außerdem
zeigte
ich,
dass
genomische
Regionen,
die
von
Zelltyp-‐spezifischer
RNA
Polymerase
II
gebunden
sind,
GFP-‐
Reporter-‐Aktivität
innerhalb
der
markierten
Zellpopulationen
zeigen,
was
darauf
hindeutet,
dass
das
RNA-‐Polymerase
II
"Profiling"
eine
geeignete
Methode
ist,
um
Zelltyp-‐spezifische
Gen-‐Aktivitäten
unterscheiden
zu
können.
Zweitens,
ich
verwendete
CAST-‐ChIP
zur
Untersuchung
der
Chromatin-‐Struktur
verschiedener
Zelltypen
und
erstellten
Profile
für
den
Einbau
der
aktiven
Histon
Variante
H2A.Z
ins
Chromatin.
Ich
fand
eine
Inkorporation
von
H2A.Z
bei
exprimierten
Genen
und
keinen
H2A.Z
Einbau
bei
inaktiven
Genen,
wie
bereits
gezeigt
wurde.
Allerdings
überlappten
die
H2A.Z
angereicherten
Regionen
nicht
vollständig
mit
den
RNA-‐Polymerase
II
Regionen.
Interessanterweise
unterschieden
sich
die
Gene,
die
von
RNA-‐Polymerase
II
jedoch
nicht
von
H2A.Z
gebunden
wurden,
in
ihrer
Expression
zwischen
sezierten
Geweben.
Daher
stellte
ich
die
Hypothese
auf,
dass
die
H2A.Z-‐
markierten
Gene
in
einer
Zelltyp-‐unabhängigen
Weise
exprimiert
werden.
Um
dies
zu
testen,
vergliche
ich
den
Zelltyp-‐spezifischen
Einbau
von
H2A.Z
mit
der
CAST-‐ChIP
Methode.
Überraschenderweise
sind
die
H2A.Z
Profile
bemerkenswert
ähnlich
in
Neuronen
und
Gliazellen,
mit
nur
etwa
hundert
signifikanten
Unterschieden.
Darüber
hinaus
ist
H2A.Z
anwesend
in
den
Regionen,
die
auch
RNA-‐Polymerase
II
in
beiden
Zelltypen
(Neuronen
und
Gliazellen)
aufweisen,
fehlt
jedoch
in
Zelltyp-‐spezifischen
Regionen.
ChIP
"Profiling"
in
einem
anderen
Zelltyp
mit
einer
unterschiedlichen
Entwicklungsherkunft
(z.B.
Fettzellen
im
Kopf)
ergab
die
gleichen
Ergebnisse.
Um
die
Resultate
durch
einen
Vergleich
verschiedener
Entwicklungsstadien
zu
validieren,
fand
ich
nur
ein
paar
H2A.Z
und
Tausende
von
RNA
Polymerase
II
unterschiedliche
Regionen
zwischen
Embryos
und
Kopfgewebe
im
adulten
Stadium.
So
ergab
die
Anwendung
von
CAST-‐ChIP
eine
neue
Funktion
von
H2A.Z
als
eine
bestimmte
Markierung
von
Genen,
die
ubiquitär
und
Zelltyp-‐unabhängig
exprimiert
werden.
Mit
Hilfe
dieser
Methode
10
Description:It would have been impossible to start, manage and finish my PhD work without his guidance and adapted a method for Drosophila, TRAP (Translating Ribosome Affinity Purification; chapter 5). the other hand, one has to be careful with GO terminology, since the annotation is far from being
