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Dok-7, MuSK, and the development of the neuromuscular junction

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1 Dok-7, MuSK, and the development of the neuromuscular junction
Paris, December 1-2, 2009 International Conference on Myasthenia Dok-7, MuSK, and the development of the neuromuscular junction Yuji Yamanashi Dept. Genetics Inst. Medical Science University of Tokyo

2 Dok-7, MuSK, and the development of the neuromuscular junction
Paris, December 1-2, 2009 International Conference on Myasthenia Dok-7, MuSK, and the development of the neuromuscular junction The receptor protein-tyrosine kinase MuSK controls where the NMJ develops. The cytoplasmic, adaptor-like protein Dok-7 is an essential activator of MuSK

3 The receptor protein-tyrosine kinase (PTK) MuSK
Ig-like domains (Agrin response) Frizzled-like cystein-rich domain （Wnt response ?） PTK domain (catalytic domain) (Jennings et al., PNAS. 90: , 1993) (Zhang et al., Develop. Cell. 16: , 1993) Dechihara …, Burdan, & Yancopoulos MuSK is essential for the development of NMJs MuSK controls where NMJs form in myotubes (DeChiara et al., Cell 85: , 1996) (Kim et al., Nat. Neurosci. 11: 19-27, 2008)

4 AChRs form postsynaptic clusters in the central region of the muscle
Myotube Nerve AChR Wild-type AChRs form postsynaptic clusters (red) in the central region of myotubes. AChR cluster （postsynaptic region） ( E18.5 Diaphragm ) MuSK is expressed in the central region of myotubes.

5 MuSK controls where the NMJs form （postsynaptic region）
Myotube Nerve AChR Wild-type AChRs form postsynaptic clusters in the central region of myotubes. MuSK Tg (overexpression in the muscle) Uniformly overexpressed MuSK induces scattered AChR cluster formation; and NMJs are also scattered. ( E18.5 Diaphragm ) (Kim et al., Nat. Neurosci. 11: 19-27, 2008) AChR cluster （postsynaptic region）

6 MuSK controls where the NMJs form （postsynaptic region）
Myotube Nerve AChR Wild-type AChRs form postsynaptic clusters (red) in the central region of myotubes. MuSK Tg (overexpression in the muscle) Uniformly overexpressed MuSK induces scattered AChR cluster formation; and NMJs are also scattered. Lin, …, sanes, and Lee (Nature 2001). MuSK KO MuSK-KO mice form no AChR cluster ( Diaphragm ) AChR cluster （postsynaptic region） (Lin et al., Nature 410: , 2001) (Kim et al., Nat. Neurosci. 11: 19-27, 2008)

7 Neural Agrin activates MuSK via LRP4 coreceptor.
(Kim et al., Cell 135: , 2008) (Zhang et al., Neuron 60: , 2008) motor nerve . motor nerve terminal Motor nerve terminal It has recently been reported that Neural Agrin activates MuSK via its coreceptor LRP4. So, motor nerve terminal secretes agrin to activate MuSK via the coreeptor LRP4. This activation somehow induces postsynaptic specialization including AChR clustering, which eventually leads to NMJ formation. However, this elegant signaling pathway has been challenged the following observation. Agrin Agrin Agrin Agrin LRP4 LRP4 LRP4 LRP4 Rapsyn AChR cluster MuSK AChR Myotube Myotube

8 Nerve/Agrin-independent but MuSK-dependent AChR clustering
WT Agrin KO HB9 KO MuSK KO (E14.5 Diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve . motor nerve terminal Motor nerve terminal Agrin Agrin Agrin Agrin LRP4 LRP4 LRP4 LRP4 Rapsyn AChR cluster MuSK AChR Myotube Myotube

9 ? Nerve/Agrin-independent but MuSK-dependent AChR clustering WT
Agrin KO HB9 KO MuSK KO (E14.5 Diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve Nerve/Agrin-independent, probably muscle-intrinsic element(s) may exist to activate MuSK . Agrin Agrin LRP4 LRP4 LRP4 LRP4 ? （　　　） Rapsyn AChR cluster MuSK AChR Myotube Myotube

10 Dok-7 Nerve/Agrin-independent but MuSK-dependent AChR clustering WT
Agrin KO HB9 KO MuSK KO (E14.5 Diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve Nerve/Agrin-independent, probably muscle-intrinsic element(s) may activate MuSK . Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 Rapsyn AChR cluster MuSK AChR Myotube Myotube

11 Dok-family High expression in hematopoietic cells High expression
Y: SH2 binding/target motif Y Y Y Y Y Y Y Y Y Y Dok-1 (62kD) PH PTB (100%) (100%) Y Y Y Y Y Y High expression in hematopoietic cells Dok-2 (56kD) PH PTB ( 40%) ( 50%) Y Y Y Y Dok-3 (58kD) PH PTB ( 50%) ( 40%) Y Y Y Y Y Dok-4 (41kD) PH PTB ( - - -) ( 30%) PH PTB Y High expression in non-hematopoietic cells Dok-5 (36kD) Suggesting a adaptor function of these proteins./ From these structural characteristics, it is suggested that these proteins play an adaptor function. ( - - -) ( 35%) PH PTB Y Dok-6 (36kD) ( - - -) ( 35%) Y Y Dok-7 (55kD) High expression in muscles PH PTB ( - - -) ( 20%)

12 Dok-1/2 Dok-1/2 (Proliferation & Cytokine Production) GM-CSFR IL-3R
TLR4 BCR SCFR M-CSFR Dok-1/2 Dok-1/2 Receptor PTKs Non-Receptor PTKs Indeed we have reported that Dok-1 and Dok-2 play adaptor functions downstream of these RPTKs and PTKs associated with receptors in blood cells. Ras-Erk (Proliferation & Cytokine Production) Yamanashi & Baltimore, Cell, 1997 Yamanashi et al., Genes Dev., 2000 Yasuda et al., J. Exp. Med., 2004, Shinohara et al., J. Exp. Med., 2005

13 Dok-family proteins High expression in hematopoietic cells
Y: SH2 binding/target motif Y Y Y Y Y Y Y Y Y Y Dok-1 (62kD) PH PTB (100%) (100%) Y Y Y Y Y Y High expression in hematopoietic cells Dok-2 (56kD) PH PTB ( 40%) ( 50%) Y Y Y Y Dok-3 (58kD) PH PTB ( 50%) ( 40%) Y Y Y Y Y Dok-4 (41kD) PH PTB ( - - -) ( 30%) PH PTB Y High expression in non-hematopoietic cells Dok-5 (36kD) ( - - -) ( 35%) PH PTB Y Dok-6 (36kD) ( - - -) ( 35%) Y Y Dok-7 (55kD) High expression in muscles PH PTB ( - - -) ( 20%) （Okada et al., Science, 2006）

14 Postsynaptic localization of Dok-7 at Neuromuscular Junction (NMJ)
gastrocnemius Presynaptic vesicle (+ACh: acetylcholine) AChR (ACh receptor) cluster myotube Dok-7 AChR Merge NMJ (Neuromuscular Junction) (-Dok-7 Ab) (bungarotoxin) motor nerve NMJ myotube MuSK AChR (Apel et al., Neuron, 1997)

15 ? ? Postsynaptic localization of Dok-7 at Neuromuscular Junction (NMJ)
gastrocnemius Presynaptic vesicle (+ACh: acetylcholine) AChR (ACh receptor) cluster myotube Dok-7 AChR Merge NMJ (Neuromuscular Junction) (-Dok-7 Ab) (bungarotoxin) Agrin-MuSK -Dok-7 signaling ? motor nerve . motor nerve terminal Motor nerve terminal Because Dok-7 is suggested to be an adaptor, we initially thought that it plays a role downstream of MuSK in NMJ development; but the data we obtained was different. Agrin Agrin Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 Dok-7 PH PH PH ? ? PTB PTB Rapsyn AChR cluster MuSK Y Y AChR Y Y Myotube Myotube

16 Dok-7 induces MuSK activation and AChR clustering in myotubes
P MuSK pY pY MuSK  pY-AChR1 AChR-PD pY Dok-7 myotubes WCL Tubulin ( ) Dok-7 （C2C12） myotubes ( AChR : ACh Receptor ) IP ： Immunoprecipitation IB ： Immunoblotting PD： Pull-down WCL： Whole cell lysates apY： anti-phosphotyrosine

17 Dok-7 induces MuSK activation and AChR clustering in myotubes
P MuSK pY pY MuSK  pY-AChR1 AChR-PD pY Dok-7 myotubes WCL Tubulin ( ) Dok-7 （C2C12） Agrin Dok-7 can activate MuSK independently of Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

18 Dok-7 Nerve/Agrin-independent but MuSK-dependent AChR clustering WT
Agrin KO HB9 KO MuSK KO (E14.5 Diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve Nerve/Agrin-independent, probably muscle-intrinsic element(s) may activate MuSK . Because this signaling event can explain Nerve/Agrin independent cluster formation of AChRs, we further questioned…. Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 Rapsyn AChR cluster MuSK AChR Myotube Myotube

19 Is Dok-7 a muscle-intrinsic activator of MuSK in vivo ?
Agrin Dok-7 can activate MuSK independently of Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

20 Dok-7 is essential for AChR clustering and NMJ formation in vivo
Nerve AChR Merge Nerve AChR Merge E14.5 WT WT Dok-7 　KO Dok-7 　KO (E14.5 diaphragm) (E18.5 diaphragm) motor nerve . Dok-7 is essential for AChR clustering and NMJ formation in vivo Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

21 Overexpression of Dok-7 in vivo
WT Tg 100 75 50 Dok-7-EGFP Dok-7 IP: Dok-7 IB: Dok-7 motor nerve . Overexpression of Dok-7 in vivo Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

22 Overexpression of Dok-7 in vivo facilitates AChR cluster formation
Nerve AChR Merge E18.5 WT Tg WT 100 75 50 Dok-7-EGFP Dok-7 Tg Dok-7 IP: Dok-7 IB: Dok-7 E18.5 Diaphragm ( Inoue et al. Science Signaling, 2009 ) motor nerve . Overexpression of Dok-7 in vivo facilitates AChR cluster formation Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

23 Overexpression of Dok-7 in vivo facilitates AChR cluster formation
Nerve AChR Merge 80 60 40 20 100 WT Dok-7 Tg WT Myofibers（％） Dok-7 Tg 1 2 3 4 5 6 7 8 9 AChR clusters per myofiber E18.5 Diaphragm ( Inoue et al. Science Signaling, 2009 ) motor nerve . Overexpression of Dok-7 in vivo facilitates AChR cluster formation Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

24 Overexpression of Dok-7 in vivo facilitates AChR cluster formation
Nerve AChR Merge AChR cluster(s) on a myotube WT WT Dok-7 Tg Dok-7 Tg E18.5 Diaphragm ( Inoue et al. Science Signaling, 2009 ) motor nerve . Overexpression of Dok-7 in vivo facilitates AChR cluster formation Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

25 Dok-7 induces NMJ formation in vivo
AChR cluster(s) on a myotube E18.5 200 150 100 50 ** **P < 0.001 WT Number of NMJs（％ of WT） Dok-7 Tg WT Dok-7 Tg ( Inoue et al. Science Signaling, 2009 ) motor nerve . Overexpression of Dok-7 in vivo facilitates NMJ formation Numbers of NMJs were increased 1.7 fold. / These findings suggest Dok-7’s ability to activate MuSK in vivo. Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

26 Dok-7 activates MuSK in vivo
pY-MuSK *P < 0.05 Dok-7 Tg WT * Relative intensity 160 120 80 40 140 100 20 60 AChR-PD (Btx) **P < 0.003 pY-AChR Dok-7 Tg WT ** Relative intensity 160 120 80 40 140 100 20 60 IB: PY IB: MuSK IP: MuSK WT Tg pY-MuSK MuSK 100 Tg Dok-7 +/+ -/ /- +/+ 50 pY-AChR IB: PY 50 AChR IB: AChR (b1) ( Inoue et al. Science Signaling, 2009 ) motor nerve . Dok-7 is an essential activator of MuSK Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

27 Dok-7 is an essential activator of MuSK
Nerve AChR Nerve AChR WT Agrin KO HB9 KO MuSK KO (E14.5 diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve . Dok-7 is an essential activator of MuSK Agrin And this observations can explain why mice lacking Agrin or motor nerves can form MuSK-dependent AChR clusters. LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

28 Why Agrin cannot induce AChR clustering in Dok-7 KO mice?
Nerve AChR Merge Nerve AChR Merge E14.5 WT WT Dok-7 　KO Dok-7 　KO (E14.5 diaphragm) (E18.5 diaphragm) motor nerve . Why Agrin cannot induce AChR clustering in Dok-7 KO mice? So, our next question was why Agrin cannot induce AChR clustering in Dok-7 KO mice. Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

29 Dok-7 may be required for Agrin-mediated MuSK activation
Nerve AChR Merge Nerve AChR Merge E14.5 WT WT Dok-7 　KO Dok-7 　KO (E14.5 diaphragm) (E18.5 diaphragm) motor nerve . Dok-7 may be required for Agrin-mediated MuSK activation And, we first examined if Dok-7 is required for Agrin-mediated MuSK activation. Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

30 Agrin-mediated MuSK activation
WT Dok-7 -/- IP: MuSK IB: pY IB: MuSK Agrin (min) 150 100 ( myotube ) Dok-7 is required for Agrin-mediated MuSK activation Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

31 Agrin-mediated MuSK activation
WT Dok-7 -/- IP: MuSK IB: pY IB: MuSK Agrin (min) 150 100 Agrin (-) Agrin (+) WT Dok-7-/- Dok-7-/ Dok-7 AChR ( myotube ) ( Inoue et al. Science Signaling, 2009 ) Dok-7 is required for Agrin-mediated MuSK activation … You can restored agrin-independent weak clustering of AChRs and Agrin-dependent enhanced cluster formation. Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

32 WT Dok-7 KO Dok-7 Dok-7 Agrin KO MuSK KO (E18.5 diaphragm) motor nerve
AChR Nerve AChR Merge Agrin KO WT Dok-7 　KO MuSK KO (E18.5 diaphragm) ( Lin et al, Nature 410: , 2001) motor nerve . Dok-7 is a key muscle-intrinsic activator of MuSK Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

33 How does Dok-7 activate MuSK from the cytoplasmic compartment ?
motor nerve . Dok-7 is a key muscle-intrinsic activator of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

34 ? How does Dok-7 activate MuSK from the cytoplasmic compartment ?
motor nerve . Dok-7 is a key muscle-intrinsic activator of MuSK LRP4 LRP4 ? LRP4 LRP4 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

35 The ectodmain of MuSK is dispensble for Dok-7-mediated activation
WT Ig Dok-7 + + pY-MuSK Y PH PTB pY-MuSK-Ig IB: pY MuSK-Ig Dok-7 WT MuSK-Ig IB: myc (MuSK) Dok-7 may target the cytoplasmic portion of MuSK IB: Dok-7 DOK-7 (293T cells) ( Inoue et al. Science Signaling, 2009 )

36 The ectodmain and transmembrane region of MuSK are dispensble for Dok-7-mediated activation
WT Ig Cyt Y PH PTB Dok-7 + + + pY-MuSK pY-MuSK-Ig IB: pY MuSK-Cyt Dok-7 pY-MuSK-Cyt WT MuSK-Ig IB: myc (MuSK) MuSK-Cyt Y PH PTB IB: Dok-7 DOK-7 (293T cells) MuSK-Ig Dok-7 ( Inoue et al. Science Signaling, 2009 )

37 Dok-7 targets the cytoplasmic portion of MuSK
The ectodmain and transmembrane region of MuSK are dispensble for Dok-7-mediated activation MuSK WT Ext Cyt Y PH PTB Dok-7 + + + pY-MuSK pY-MuSK-Ig IB: pY MuSK-Cyt Dok-7 pY-MuSK-Cyt Dok-7 targets the cytoplasmic portion of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

38 Does Dok-7 directly activate the cytoplasmic portion of MuSK?
Dok-7 targets the cytoplasmic portion of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

39 Dok-7 targets the cytoplasmic portion of MuSK
MuSK-cyt Y PH PTB Dok-7 250 150 100 75 Dok-7 50 37 MuSK-Cyt 25 (kDa) (CBB) Dok-7 targets the cytoplasmic portion of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

40 Dok-7 directly activates the cytoplasmic portion of MuSK
MuSK-cyt Dok-7 MuSK-cyt pY-Dok-7-His pY-MuSK-cyt IB: pY 75 50 37 25 (min) Y PH PTB MuSK-Cyt pY: phosphotyrosine ( Inoue et al. Science Signaling, 2009 ) Dok-7 directly activates the cytoplasmic portion of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

41 Dok-7 directly activates the cytoplasmic portion of MuSK
MuSK-cyt Dok-7 MuSK-cyt Dok-7DN MuSK-cyt pY-Dok-7-His pY-MuSK-cyt IB: pY 75 50 37 25 (min) Y PH PTB (min) pY-MuSK-cyt IB: pY MuSK-Cyt pY: phosphotyrosine ( Inoue et al. Science Signaling, 2009 ) Dok-7 directly activates the cytoplasmic portion of MuSK LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

42 （postsynaptic region）
＊ Myotube Nerve AChR Merge WT WT Dok-7 Tg Dok-7 Tg Overexpression of Dok7 AChR cluster （postsynaptic region） E18.5 Diaphragm ( Inoue et al. Science Signaling, 2009 ) motor nerve . Why uniform overexpression of Dok-7 facilitates centrally formation of the NMJ ? Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

43 Is MuSK expressed in the central region of Dok-7 Tg muscle?
＊ Myotube Nerve AChR Merge WT WT Dok-7 Tg Dok-7 Tg Overexpression of Dok7 AChR cluster （postsynaptic region） E18.5 Diaphragm ( Inoue et al. Science Signaling, 2009 ) Is MuSK expressed in the central region of Dok-7 Tg muscle?

44 MuSK is expressed in the central region of Dok-7 Tg muscle, and
Dok-7 is essential for mid-muscle expression of MuSK and AChR WT Dok-7Tg Dok-7 -/- WT Dok-7Tg Dok-7 -/- E14.5 E14.5 E18.5 E18.5 in situ hybrid. (Diaphragm) MuSK AChRa MuSK is expressed in the central region of Dok-7 Tg muscle, and Dok-7 is required for the centrally restricted expression of MuSK and AChR

45 Dok-7 is essential for mid-muscle expression of MuSK and AChR
WT Dok-7Tg Dok-7 -/- WT Dok-7Tg Dok-7 -/- E14.5 E14.5 E18.5 E18.5 in situ hybrid. (Diaphragm) MuSK AChRa Immunostaining (Diaphragm) scale bar: 100 mm

46 Dok-7 is essential for mid-muscle expression of MuSK and AChR
WT Dok-7Tg Dok-7 -/- WT Dok-7Tg Dok-7 -/- E14.5 E14.5 E18.5 E18.5 in situ hybrid. (Diaphragm) MuSK AChRa Dok-7 regulates the mid-muscle NMJ formation by controlling MuSK activity, expression pattern, and responsiveness to Agrin. LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

47 A simplified model of Dok-7-MuSK-Agrin signaling in the NMJ formation
Ⅰ Ⅲ Motor nerve ACh Agrin ACh MuSK MuSK LRP4 Dok-7 Dok-7 (myotube) (myotube) Dok-7 is expressed in the central region of skeletal muscle, where it activates MuSK and induces MuSK’s mid-muscle pattern formation. ACh disperses non-innervated AChR clusters but the local mediator Agrin fully activates Dok-7-primed/activated MuSK and counteracts ACh. Ⅱ Ⅳ Motor nerve AChR agonist, carbachol (CCh), can protect NMJs in ex vivo organotypic culture of diaphragm (+ ribcages); they described the dual role of ACh/AChR in NMJ development. Agrin MuSK AChR ACh MuSK Dok-7 Rapsyn Dok-7 (myotube) Activated MuSK induces postsynaptic specialization in the central region of 　muscle independently of nerve and Agrin. (myotube) Dok-7-MuSK-Agrin triad signaling promotes and reinforces NMJ formation.

48 AChR agonist, carbachol (CCh), can protect NMJs in ex vivo organotypic culture of diaphragm (+ ribcages); they described the dual role of ACh/AChR in NMJ development.

49 Dok-7 Tg rescues NMJs in Dok KO mice
Nerve AChR Merge Nerve AChR Merge WT WT Dok-7 -/- Dok-7 Tg Dok-7 -/- + Dok-7 Tg ( Inoue et al. Science Signaling, 2009 ) E14.5 Diaphragm (unpublished) motor nerve . Dok-7 Tg rescues NMJs in Dok KO mice MuSK型のCMS や MuSK抗体陽性のMGに対する適用も視野にいれている。少なくとも、Dok-7型筋無力症のモデルマウスは作成中で、MuSK型筋無力症のモデルマウスはある Agrin Agrin LRP4 LRP4 LRP4 LRP4 Dok-7 PH PH PH PH PTB Dok-7 PTB PTB Rapsyn AChR cluster MuSK Y Y Y AChR Y Y Y Myotube Myotube

50 Dok-7, MuSK, and the development of the neuromuscular junction
Paris, December 1-2, 2009 International Conference on Myasthenia Dok-7, MuSK, and the development of the neuromuscular junction Dok-7 is an essential, muscle-intrinsic activator of MuSK, in NMJ development Enhanced Dok-7 signaling may ameliorate DOK7 and MuSK-related myasthenia

51 (Inserm, Inst. Myologie) Masakatsu Motomura Irokazu Shiraishi
Collaborators David Beeson Jackie Palace Angela Vincent (Oxford Univ.) Peter Fawcett Clarke Slater (Univ. Newcastle) Juliane S. Muller Hanns Lochmuller (Ludwig-Maxim. Univ.) Frederic Chevessier Veit Witzemann (Max-Planck Inst. Med.) Daniel Hantai (Inserm, Inst. Myologie) Masakatsu Motomura Irokazu Shiraishi Katsumi Eguchi (Nagasaki Univ.) Takashi Okada Shin’ichi Takeda (Natl. Inst. Neurosci.) Shigeru Kakuta Sachiko Kubo Yoichiro Iwakura Takafumi Jigami Tetsu Akiyama (Univ. Tokyo) ・Osamu Higuchi ・Akane Inoue Kiyoko Setoguchi ・Johko Hamuro ・Kumiko Okada

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