Axonal transport, synapse development and mental retardation
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Axonal transport, synapse developmentand mental retardation
Yong Q. Zhang
Institute of Genetics and Developmental Biology Chinese Academy of Sciences
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Mental retardation(Intellectual Disability, Cognitive Disorder)
a generalized disorder, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors with onset before the age of 18. 1-3% of general population is mentally retarded
from wikipedia.com
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82 MR genes on the X-chrom.
Chiurazzi et al., EJHG, 2008
Syndromic MR: black Non-syndromic MR: *greyMR with neuromuscular defects: +grey
CUL4B
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Chiurazzi et al., EJHG, 2008
Molecular Functions of MR Genes
1
2
3
35
✓
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Transcriptional/translational Cell-cycle-related Ros/Rho/PSD95
Nature 2011
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Neuronal functions of MR-related genes
1, Neurogenesis (microcephaly)
2, Neuronal migration (Lissencephaly)
3, Synapse formation and plasticity
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Neuronal functions of MR-related genes
1, Neurogenesis (microcephaly)
2, Neuronal migration (Lissencephaly)
3, Synapse formation and plasticity
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Synapse dysgenesis in MR patients
Purpura, Science, 1974Dendritic spines
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Mutations in ACSL4 are associated with non-syndromic X-linked mental retardation
Meloni et al., Nat Genet, 2002Longo et al., J Med Genet, 2003
aa
Splicing mutant resulting in truncation
ACSL: Acyl-CoA Synthetase Long-chain (C12-20)
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ACSL in Lipid Synthesis and ATP Production
Fatty acid
Acyl-CoA
Coenzyme A
Glycerol-3-P
Diacylglycerol (DAG)
Triacylglycerol (TAG)
PC, PE, PS
Lipid droplet
MembraneComponents
Fatty acid
Acyl-CoA
Coenzyme A
β-oxidation
ATP
ACSL
ACSL
Endoplasmic Reticulum Mitochondria
Lipid biosynthesis Fatty acid degradation
Phosphatidic acid (PA)
Coleman et al., Annu Rev Nutri, 2000
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The role of ACSL4 in neurodevelopment?
The mechanism of how the disease develops?
ACSL Family
ACSL1, 5, 6 ACSL3, 4
{subfamilies
no mouse models
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50% identity and 67% similarity
Zhaohui Wang and colleagues, Hum Mol Genet, 2009
ACSL Family: 1, 3, 4, 5, and 6
ACSL1, 5, 6 ACSL3, 4 (fly dAcsl)
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Larval Neuromuscular Junctions
NMJ synapses
Muscles
Large, simple and accessible
Griffth and Budnik, 2006
Nerves and NMJ synapses
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Axonal accumulation of synaptic vesicle protein CSP in dAcsl mutants
Wild type
dAcsl
Ubi. rescue
Khc, DhcWT
Hurd and Saxton, Genetics, 1996Martin et al, Mol Cell Biol, 1999
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A Control
B1 dAcslKO/05847
B2
OK6>Syt-eGFP ChAT
B3
B2’
B3'
B1’
A’
OK6>Syt-eGFP
ChAT
merge
20 μm
Distally-Biased Axonal Aggregates of SVs
ChAT: choline acetyltransferase
Motor Neu
Sens. Neu
Anterior Posterior
Sensory NeuronMotor Neuron
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SV protein
Dynein
Active zone
t-SNARE
Mitochondria
Cell adhesion
Accumulation of selective axonal cargos
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Retrograde cargos accumulated in dAcsl mutants
MVB:Multiple vesicle body
PLB:Prelysosomal body
Lb:Lamellated body
.
..
..
..
..
.
..
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Late endosome/lysosome
Autophago-some
MVBs
Retrograde cargos accumulated in mutants
Lysosome+autophagosome Multiple vesicle body
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dAcsl mutations lead to specific accumulation of retrograde cargoes
Synaptic vesiclesAutophagosomeLysosome
Immunostaining and EM analysis
Why did the axonal aggregates of retrograde cargos form in dAcsl mutants?
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Live imaging of axonal transport of GFP-tagged synaptic vesicles
Flux
Velocity
Processivity
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Retrograde transport of synaptic vesicles was impaired in dAcsl mutants
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Axonal transport of mitochondria was normal in dAcsl mutants
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FR
WT dfmr1 NOE WT dfmr1 NOE
Tim
e p
erce
nta
ge
*
**
*
*
AT RT
Stop
RR
E
10 m
CA B
time
Anterograde Retrograde
50 s
C,A, B,
AT RT
***
***
Flu
x (m
ito.
nu
mb
er/m
in)
*
*
WT
dfmr1
NOE
D
WT dfmr1 dfmr1 overexpres.
Yao et al., Hum Mol Genet, 2011
dfmr1 regulates axonal transport of mitochondria
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Role of axonal transport in neurodegenerative diseasesDe Vos et al., Annu Rev Neurosci, 2008
Axonal transport and neurodegenerative diseaseChevalier-Larsen and HolzbaurBiochim Biophys Acta, 2006
SV transport defects in dAcsl mutants
Mitochondria transport defects in dfmr1 mutants
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Accumulation of retrograde cargoesand transport defects
?
Defects in synaptic development and function
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Larval Neuromuscular Junctions
NMJ synapses
MusclesLarge, simple and accessible
Griffth and Budnik, 2006
Nerves and NMJ synapses
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dAcsl mutants show atrophic synaptic terminals
Neuronal but not muscular rescue by human ACSL4
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dAcsl is required for NMJ growth and stability
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Pre- and post-synaptic components concomitantly reduced in dystrophic NMJs
No increased apoptosis
Futsch/MAP1B active zone protein Postsynaptic scaffold
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CNS
7 6
NMJ
Nerve stimulation
Vm
I Postsynaptic current (EJC)
Nerve
Will atrophic NMJs show defective transmission?
mEJP: miniature EJPs
Spontaneous release of single SVs
EJP:Excitatory Junction Potentials
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dAcsl mutations impaired neurotransmissionEJP: Excitatory Junction Potentials
mEJP: miniature excitatory junction potentials
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dAcsl mutations impaired neurotransmission
Neuronal but not muscular rescue by human ACSL4
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Axonal jam and retrograde transport defects
NMJ synapse atrophy
Reduced neurotransmission
Can these phenotypes be corrected by induced expression?
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Drug-induced tissue specific expression
Osterwalder et al., PNAS, 2001
Gal4
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Aggregates were rescued by induced expression
Together with NMJ rescue
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dAcsl mutants show distally-biased axonal aggregates and impaired retrograde transport of synaptic vesicles
dAcsl is required for synaptic growth, stability
and neurotransmission
Summary
Liu et al., J Neurosci., 2011
SVSVSVSVSVSV
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AcknowledgmentsZhihua Liu, PhD
Yan Huang
Zhaohui Wang (PI)
Yi Zhang (mutants & Ab)
Di Chen (mutants)
Zhihua Liu
Yan Huang
Grants:
National Science Foundation of China
Chinese Academy of Sciences
The Ministry of Science and Technology
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Acyl-CoA is central to diverse processes
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K294E
Q419R
W685@
R570S
P375L
V594D
dACSL-8 dACSL-1 mutations in patients
Conservation is not restricted