The FMR1 disorders (Fragile X syndrome, etc)

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The FMR1 disorders(Fragile X syndrome, etc)
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• Mary Beth Busby
• founding board member of the Fragile X Research
  Foundation (FRAXA)
• Walter Kaufmann
• Director, Center for Genetic Disorders of
  Cognition and Behavior, Kennedy Krieger
  Institute, The Johns Hopkins University
• Karen Usdin
• Chief, Gene Structure and Disease Section
• LMCB, NIDDK

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Understanding the molecular basis of the FMR1
gene disorders
exon 1
intron 1
promoter
5 UTR
X chromosome
(CGG)n
Karen Usdin
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FXPOI
FXPOI
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The Repeat Expansion Diseases
(CGG)n
(CTG)n
(CAG)n
(GAA)n
(ATTCT)n
(C4GC4GCG)n
(CCTG)n
ORF
3 UTR
Intron
Promoter
5 UTR
O
R
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gametogenesis
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Premutation symptoms result from RNA toxicity

• The RNA is somehow deleterious
• the CGG-repeats may
• trigger deleterious processes
• sequester proteins that are important for normal
  neuronal and ovarian function

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RNA toxicity hypothesis

• The RNA is somehow deleterious
• the CGG-repeats may initiate or trigger
  deleterious processes
• the CGG-repeats may sequester proteins that are
  important for normal neuronal and ovarian
  function

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RNA interference
Hannon (2002)
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SK cells
SK cellsCGG88
DAPI
lamin
merge
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Is FXTAS a laminopathy?

• mutations in Lamin A/C are associated with one
  form of Charcot-Marie-Tooth disease, a
  neurological disorder
• other mutations in Lamin A/C result in premature
  aging

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Gene silencing in mammals
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Science, 1991
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What does FMRP do?
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• learning difficulties
• macroorchidism
• altered circadian rhythms
• rapid early growth rate
• audiogenic seizures
• anxiety

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WT
KO
Qin and Beebe-Smith (NIMH)
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FMRP structure
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RNAs bound by FMRP

• FMR1
• Glucocorticoid receptor
• GABAA receptor subunits
• CAMKIIa
• MAP1B
• Rac1
• Calbindin
• Vimentin
• etc, etc

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FMRPI304N
FMRP
-
protein product
Protein gel
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Increased rates of cerebral glucose metabolism in
a mouse model of fragile X mental retardation
Nissl staining
14C DG
WT
KO
Qin, Kang, and Beebe Smith (2002) (NIMH)
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Results of fishing for FMRP interacting proteins

• FXR1P
• FXR2P
• CYFIP1 and CYFIP2
• Poly(A)-binding protein
• eIF2C2/AGO1
• Dicer
• kinesin heavy chain

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RNA interference
Hannon (2002)
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Grazyna Gorny
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Synaptic transmission
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Dendritic Spine Structural Anomalies in Fragile-X
Mental Retardation Syndrome Irwin, Galvez and
William T. Greenough Cerebral Cortex (2000)
FXS
Un
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Results of fishing for FMRP interacting proteins

• FXR1P
• FXR2P
• CYFIP1 and CYFIP2
• Poly(A)-binding protein
• eIF2C2/AGO1
• Dicer
• kinesin heavy chain

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RISC
FMRP
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Minocycline
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Metalloproteinase-9 (MMP-9)
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Take home messages

• FXTAS and FXPOI result from repeat-induced
  hyperexpression of the FMR1 gene and the
  deleterious effects of high levels of CGG-repeat
  containing mRNA.
• FXS results from repeat-induced gene silencing.
• silencing leads to a deficiency of FMRP, a
  protein important for the regulation of
  translation in the synapses of neurons
• the resultant abnormal expression of proteins
  like mGluR5, GSK-3, GABAA and MMP-9 results in
  the symptoms of FXS
• normalizing expression of these proteins may
  provide targeted approaches to the treatment of
  FXS.

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