Overview. Introduction - Background. Introduction - Background. Introduction - Aims. Transgenic Mice Generated

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1 Overview Wallerian Degeneration of Injured Axons and Synapses is Delayed by a Ube4b/Nmnat Chimeric Gene Mack T, Reiner M, Beirowski B, Weiqian M, Emanuelli M, Wagner D, Thomson D, Gillingwater T, Court F, Conforti L, Fernando F. S, Tarlton A, Andressen C, Addicks K, Magni G, Ribchester R. R, Perry V. H and Coleman M. P. Introduction Background Information Aims Discussion Future Research Questions Introduction - Background Introduction - Background Distal axons of injured neurons usually undergo Wallerian degeneration hours after injury. In C57BL/Wld s mice, injured axons can survive several weeks following injury. This suggests that these mice have a protective mechanism specific to the axons, and that this protective factor must be present in the axon prior to any injury occurring as the distal part of the axon is separated from the cell body and cannot benefit from new protein synthesis. Wallerian degeneration is implicated in several human neuropathologies. These include ALS, multiple sclerosis and traumatic disorders such as injury to the spinal cord An understanding of the mechanisms controlling the slow Wallerian degeneration exhibited by the C57BL/Wld s mouse could lead to the new therapeutic targets for such diseases. A candidate Wld s gene was identified on chromosome 4 (mouse) It is a chimeric gene containing coding regions for Ube4b/D4Cole1e in the mouse D4Cole1e was found to be equivalent to the human enzyme Nmnat. Both proteins were found to be expressed in Wld s mice, strongly suggesting that this chimeric gene is the Wld s gene Introduction - Aims Hypothesis: the Ube4b/Nmnat chimeric gene is the Wld s gene and produces the slow Wallerian degeneration phenotype observed in the mutant mice. To test this, the chimeric gene was expressed in transgenic mice. Several strains of mice were produced, each with a different expression level of the chimeric gene. Transgenic Mice Generated 4 lines of transgenic mice were generated for this study: 4839, 4830, 4858 and In each line, the expression level of the chimeric gene had been altered. The lowest level was expressed in 4839; 4830 and 4858 showed a medium level of gene expression (only 4830 is further discussed in the paper); 4836 had the strongest expression which is almost identical to Wld s mouse.

2 Structural Preservation of Transected Axons Structural preservation was investigated 3-5 days following a unilateral lesion to the sciatic nerve. Electron microscopy showed that the vast majority of axons in the 4836 mouse had preserved cytoskeletons 5 days after injury Successful replication of the Wld s phenotype. WT mice showed clear signs of degeneration in myelinated and unmyelinated axons. Partial protection was observed as expected in 4830 axons Functionally Competent Motor Axons and Synapses Tested whether the motor axons were still functional as well as structurally preserved. Using intracellular recordings, the response of the muscle to nerve stimulation and the generation of action potentials were recorded No evidence of motor axons still functioning in WT mice. In transgenic mice, there was evidence of functioning motor axons and synapses for at least three days after injury. In homozygous 4836 mice, nerve stimulation led to a functional response in 80% of muscle fibres 3 days after injury. In heterozygous 4836 mice and 4830 mice, the percentage of muscle fibres which responded to nerve stimulation after injury were significantly lower than the 4836 mouse, and the duration after injury which the axons and synapses appeared functional was also reduced. Functional motor axons and synapses were visualised using immunostaining methods Homozygous 4836 mice demonstrated synaptic vesicle recycling 5 days after injury, indicating synaptic transmission is still able to occur. Homozygous 4836 mice also showed a high proportion of endplates fully occupied 5 days after injury. Proportion of endplates occupied were reduced in hemizygous 4836 mice and in 4830 mice.

3 Protection Depends on Wld Protein Expression Levels The level of Wld protein expression in the mutant strains was quantified using a Western blot analysis. Homozygous 4836 mutant mice showed similar expression of the protein to the Wld s mouse, again confirming that the Wld s phenotype was successfully recreated. Other strains showed dose-dependent expression of Wld protein. Homozygous 4836 mutant mice also demonstrated a higher proportion of intact axons 5 days after sciatic nerve lesion compared to other stains, which were visualised using electron microscopy. To further test how expression levels of Wld protein protects axons from degeneration, the degree of neurofilament degradation (measured by Western blot) and the number of intact axons (electron microscopy) were measured after days. In Wld s and homozygous 4836 mice, neurofilament degradation was less than that of other strains. In homozgous 4836 and Wld s mice, axon protection was significantly better than that of WT and other mutant strains. Wld is a Predominantly Nuclear Protein Wld protein was found to be localised in the nucleus of Wld s and transgenic mice, using immunostaining methods. It was not located in the nucleus of WT mice. There was no detection of Wld protein in the axons of any mouse strain. This study did not find evidence of Wld expression in glial cells, but previous studies have reported detecting Wld protein in Schwann cells using RT-PCR Wld may have roles other than axon protection in other cell types

4 The Wld protein has Nmnat Enzyme Activity Intrinsic Nmnat activity was initially measured using recombinant protein expression and measuring the activity of the bacterial lysate. In Wld s mice, Nmnat levels were measured in brain homogenates and were found to be four times higher than the control. Total NAD+ levels were not significantly increased however, indicating that Wld protein increases Nmnat levels but not overall NAD+ levels. Conclusions The paper concludes that the Ube4b/Nmnat chimeric gene has been successfully identified as the Wld gene. The Wld s phenotype was successfully recreated in the homozygous 4836 transgenic mouse. It was also shown that the level of expression of the Wld protein directly relates to the level of axon protection. Wld protein was found to be localised in the nucleus and that it protects axons through an indirect mechanism involving other factors. Discussion And Further Research The role of Ube4b and Nmnat As the Wld protein is located in the nucleus, the actions of Ube4b and Nmnat may be influence downstream regulatory pathways, which can then go on to directly influence axon protective mechanisms. Ube4b is involved in ubiquitination processes may produce protective effects by influencing the stability of protein-protein interactions or RNA, or by affecting nuclear transport. Nmnat levels in Wld s mice is increased, but NAD+ levels remain similar to that of WT. This suggests that the NAD+ is being metabolised. These metabolites may produce neuroprotective effects. Discussion And Further Research Wld Protein as a Therapeutic Target Wld s phenotype is known to protect axons from toxic effects of vincristine. Studies have also indicated that Wld s protects against a mouse model of motor neurone disease. From the identification of the Wld gene, and through investigation into the mechanisms through which Wld protein exerts its neuroprotective effects, therapeutic targets for several neuropathologies could be identified. Questions How could nuclear Wld s protect severed axons? What is the significance of constant levels of NAD+? Is the ubiquitin-proteasome system involved? Nuclear Wld s most likely protects severed axons by altering regulatory pathways prior to the axon being severed. The constant NAD+ levels observed in Wld s mice indicate that a significant proportion of NAD+ is being metabolised. Metabolites of NAD+ are known to exert both neuroprotective and neurotoxic effects. Ube4b is a multi-ubiquitinating enzyme. Although the full Ube4b gene is not expressed in the chimeric gene, it is likely that the role of Ube4b in Wlds is likely to be similar to that of the regular enzyme. Therefore, there is a strong possibility that the ubiquitinproteasome pathway is involved in the protection of axons; possibly through degrading proteins which produce or enhance the process of Wallerian degeneration

5 Age-dependent synapse withdrawal at axotomised neuromuscular junctions in Wld s mutant and Ube4b/Nmnat transgenic mice Thomas H. Gillingwater*, Derek Thomson*, Till G. A. Mack, Ellen M. Soffin*, Richard J. Mattison*, Michael P. Coleman and Richard R. Ribchester* Journal of Physiology (2002), 543.3, pp DOI: /jphysiol The Physiological Society 2002 Outline Intro/background Aims/hypothesis Methods Conclusion Strengths/weaknesses BBQs Summary Mairi Laverty Background Aims and Hypothesis Wallerian degeneration: the molecular and cellular responses that are involved in the degeneration of distal axons and synaptic terminals after lesion or injury Wld s mutation: overexpression of a chimeric Ube4b/Nmnat (Wld) gene that protects axons from Wallerian degeneration Wld s mutation is inherited as a single autosomal dominant characteristic, by a gene located on the distal end of chromosome 4. Protection differs in axons and synapses after axotomy: in Wld s mice the motor nerve terminals persist for only 4-10 days while distal axons persist up to 3 weeks Thought to be differences in protection for age as well Previous controversy whether age affected the neuroprotective role of the Wld s gene Aim: to resolve the discrepancy between the studies of Ribchester et al. (1995) and Crawford et al. (1995) using a combined genetic, biochemical, morphological and electrophysiological approach. Methods Mice: natural mutant Wlds mice, some used at around 1-2 months old, whereas others were kept to older ages (4,7 and 12 months) Surgery: FBD or lumbrical muscles=either sciatic or tibial nerve exposed and partly removed (denervating the majority of muscles in hind foot); TA= intercostal nerves were similarly exposed and lesioned. Electrophysiology: intracellular recordings were made 1-10 days after surgery Electron Microscopy: special preparations then viewed through Phillips CM12 TEM. Axon Counts: cross sections were cut, stained and examined. Total number of myelinated axon profiles were recorded in 6 cross-sections NMJ staining: preparations were fixed then acetylcholine receptors were labelled, Fluorescence imaging and analysis: used standard fluorescence microscope or laser scanning confocal microscope Western Blotting of mouse brains

6 Sections Age-independence of axon protection and Wld gene expression Progressive loss of synaptic terminals in juvenile Wld s mice Rapid degeneration of Wld s synatpic terminals in mature mice Recapitulation of synaptic withdrawal at reinnverated Wld s muscles Age dependence of synaptic protection in Wld transgenic mice Protection of axons and synapses expressing fluorescent protein by the Wld gene Age-independence of axon protection and Wld gene expression Figure 1: A: Western Blots= age has no effect on Wlds gene expression B: shows qualitative preservation of disconnected axons; no difference in age for axon loss or degeneration after axotomy C: no significant difference in numbers of axon profiles between proximal and distal nerve stumps at either age Data shows that both Wld gene expression and distal axon preservation are largely independent of age in Wld s mice. Progressive loss of synaptic terminals in juvenile Wld s mice Figure 2: Axotomized nerve terminals retract from endplate in young adult Wlds mice A: synapses protected from degeneration, 3 days after B: complete retention of lower nerve terminal but partial occupancy of the upper endplate, 6 days post-axotomy C: retraction bulb= also found in synapse elimination D: 2 vacant endplates and 2 fully occupied, 6 days after E: EM of nerve terminal bouton F: retained good synaptic ultrastructure but neurofilaments are accumulated in the centre of the bouton Figure 3: time course of withdrawal in 2 month old Wld s mice -Measured morphologically and electrophysiologically -80% of synapses were retained 3 days after axotomy but by 5 days this dropped to 60% then 30-50% by 7 days. G: partially occupied NMJ, neighbours re unoccupied and covered by the nucleus of a terminal Schwann cell H-J: intracellular recordings: robust transmission, weak transmision and loss of transmission Figure 4: Effect of endplate size and occupancy on synaptic withdrawal A: Withdrawal of synaptic boutons was asynchronous and independent of endplate size -no correlation between endplate area and fractional occupancy Onset of synapse withdrawal occurred randomly but proceeds at a constant rate once started B: Depression of transmitter release preceeded structural withdrawal Still occupied but low quantal content Synaptic terminals in the young Wld s mice progressively withdrew from motor endplates following axotomy Similar to synapse elimination that occurs during normal post-natal development Time course is also similar Rapid degeneration of Wld s synaptic terminals in mature mice Figure 5: Degeneration of synaptic terminals in fully mature Wlds mice Axons are removed synchronously in old mice compared to progressively in younger mice, therefore axotomy-induced synaptic response in Wld s mice changes systematically; from withdrawal to degeneration as these mice mature.

7 Recapitulation of synaptic withdrawal at reinnervated Wld s muscles Figure 6 D and E: Figure 6: Synaptic protection in Wlds mice depends on synaptic maturity and not the age of the animal B: 7 month old 3 days post axotomy: one of the few remaining terminals next to 3 vacant endplates C: 14 month old regenerated synapse 5 days post axotomy: all endplates are occupied new synapses in old Wld s mice are better protected form degeneration than the mature synapses innervating muscles without a prior, conditioning lesion applied to the nerve -Therefore it is the maturity of the nerve not the age. Age dependence of synaptic protection in Wld transgenic mice 2 transgenic lines of Wld mice: lines 4836 and 4830 which show the Wld phenotype Examined the age dependence of synapse loss: Wld s expression and axon preservation independent of age intracellular recordings show the same age dependence in synaptic response to axotomy as seen in Wld s mice, with a similar time constant Overall similar to natural mutant Wld s mice Useful for future studies Protection of axons and synapses expressing fluorescent protein by the Wld gene Available mice that can express fluorescent protein in their axons and synapses under control of a thy1 promoter. Allows us to see axon and synaptic protection in living preparations Crossbred Wld s mice and thy1-cfp mice Fluorescent protein expression did not interfere with the protection of axons and synapses presented by the Wld gene in young mice. Degree of protection was similar to Wld s mice not expressing CFP Shows future potential Main Findings/Discussion Conclusions the main finding of the present study is that lesions of peripheral nerve induce one of at least two independent modes of synaptic degeneration in Wld-expressing mice, depending on the maturity of the synapses that are axotomised. Support Crawford et al., 1995: axonal loss is independent of age BUT preservation of axotomised Wlds nerve terminal is strongly age-dependent. Axons are protected from degeneration at all ages but synapses are not which suggests that both mechanisms of synaptic degeneration occur independently of axonal degeneration. Further support that the neurones are compartmentalised with respect to the mechanisms they contain for bringing about degeneration Wld gene expression and axon protection is age independent Loss of synaptic terminals is progressive in juvenile Wlds mice and similar to synapse elimination Degeneration of Wld s synaptic terminals in mature mice is rapid and not progressive new synapses in old Wld s mice are better protected after conditioning lesion= it is maturity of the synapse rather than age of the motor neuron or mouse Transgenic mice show same age dependence as natural mutant Wlds mice Fluorescent protein expressing mice also show the same protection of axons and synapses

8 Strengths and Weaknesses Strengths: Discovered useful methods for future research: transgenic and fluorescent mice solve controversies over previous thoughts on age dependency of synapse withdrawal Weaknesses: Did not mention sample size BBQs Why does the Wld s phenotype decline with age? What mechanisms might produce recapitulation of the juvenile Wld s phenotype at regenerating synapses in old mice? Why does the Wld s phenotype decline with age? It is actually the maturity of the synapse not the age that seems to play the important role Reasons are unknown but perhaps: Biochemical state of the regenerated terminal and local regulation of the response to axotomy, or to recapitulation of patterns of gene expression in motor neurone nuclei What mechanisms might produce recapitulation of the juvenile Wlds phenotype at regenerating synapses in old mice? Axonal and synaptic protection is an indirect mechanism and does not interact with other genes that are uniquely expressed in axons and synapses, as the Wld protein is localised to the cell nuclei incorporation of a ubiquitination cofactor (the N-terminal 70 amino acids of Ube4b) in the Wld gene could play an important role in degeneration and response to synaptic axotomy. One hypothetical link: perhaps selective physiological trafficking of maintenance factors during early postnatal development (or after reinnervation) results in the same withdrawal response as that induced by surgical axotomy in young Wld s mice. Could have molecular mechanisms or physiological trafficking when the synapse or axon is newly innervated compared to when it has been present for a while such as in a mature mouse. Future Studies The use of thy1-cfp mice could be very useful in future studies to visualise axotomy-induced synapse withdrawal in real-time Transgenic mice also hold significant value for future studies More studies into the role of protein ubiquitination in synapse withdrawal The relationship of neuromuscular synapse elimination to synaptic degeneration and pathology: Insights from Wld(s) and other mutant mice: Thomas H. Gillingwater and Richard R. Ribchester Could it relate to humans and have therapeutic potential for neurodegenerative diseases Summary: Take home message 2 modes of synaptic degeneration depending on maturity of the synapses that are axotomised: Progressive withdrawal in young and Wallerianlike in mature mice

9 References This article: ac.uk/doi/ /jphysiol /abstract Subsequent study: 282/ Crawford s conflicting study: 6v13/ Questions? Non-Nuclear Wld s Determines its Neuroprotective Efficacy for Axons and Synapses In Vivo Beirowski et al, 2009 Presented by Jen Sturgess Introduction Aim Methods Conclusions Big Burning Question Strengths/Weaknesses Future work Intro Wld s delays axon degeneration trying to discover mechanisms Wld s found to be abundant in only cell nuclei, suggesting indirect axonal effects of the protein However, absence in other structures not proven experimentally due to detection limits in subcellular compartments, therefore may be present Where are the Wld s subcellular sites of action? Intro Important point - study is in vivo Some in vitro studies show overexpressed Nmnat has similar neuroprotective effects to Wld s, however in vivo this is not the case Differences between in vivo and in vitro in vivo makes more clinically relevant

10 Aim Create transgenic mice with reduced nuclear targeting and cytoplasmic redistribution of Wld s show differences between WT, native Wld S and ΔNLSWld S mice after nerve lesion To find the subcellular location of Wld s action in vivo Investigate neuroprotective effects of extranuclear Wld S Methods Created ΔNLS Wld s mice widespread Wld s axon distribution 2 point mutation (R213A, R215A) within the NLS of the Nmnat1 domain (Δ NLS = deleted nuclear localisation sequence) Tested in vitro and in vivo for expression of Wld s variants Confirmed reduction of Wld s protein in the nucleus through cell culture of hippocampal and dorsal root ganglion, and HeLa and PC12 cells showed almost complete exclusion of Wld s from the nucleus Methods Biochemical assessment of variant Wld s protein levels in transgenic mice Segments from brain, lumbar spinal cord and sciatic nerve were sampled Tissue was homogenized and centrifuged Levels of protein were measured in Nuclear fraction Cytoplasmic fraction Cytosolic fraction Nuclear and postnuclear fraction Cytoplasmic and mitochondria-enriched fraction Microsome-enriched and cytosolic fraction Measurement were quantified using integrated optical density (OD) of bands from 3 blots per experimental group Methods Assessment of axon preservation Right sciatic nerves transected or crushed in wild type, Wld s native and ΔNLS Wld s mice Tested structural preservation using confocal microscopy of a YFP-labelled axon subset Also tested using light/electron microscopy Evaluated axonal integrity Methods Electrophysiology and vital labeling of NMJs To test whether NMJs were preserved after axotomy, they recorded muscle contractions, electromyography and vital labeling of synaptic terminals Preparations of tibial nerve flexor digitorum brevis (FBD) used FBD preparations also stained and stimulated for morphological quantification of functionally preserved NMJs Acetylcholine receptors stained and endplate occupancy quantified Methods Immunocytochemistry and immunohistochemistry Immunofluorescence detection of Wld S variant expression Special techniques for high-sensitivity detection of low abundance Wld S protein variants Nonfluorescent immunohistochemically stained tissues were imaged Confocal imaging and fluorescence intensity quantification Immunostained tissue sections and vital dye-labelled muscle preparations were imaged

11 Figure 1 Lots of tests to make sure they had created the neuroprotective phenotype they wanted Breeding to homozygosity elevated ΔNLSWld S protein expression in brain by approx twofold compared to hemizygosity Expressed full Nmnat enzyme activity Significantly reduced nuclear targeting and relative cytoplasmic redistribution of Wld S protein The strength of axon protection is closely related with levels of Wld S If Wld S works through a nuclear mechanism, then hypothesised that reduction of nuclear Wld S would decrease axon protection However the opposite happens redistribution away from nucleus increases axonal protection ΔNLSWld S delays wallerian degeneration more robustly than native Wld S Figure 2 Figure 4 Figure 3. Time course of Wallerian degeneration at 3, 5 and 14 days following sciatic nerve transection Confocal images of lesioned sciatic/tibial nerves Wld S heterozygotes = pronounced degradation from 21 days Wld S homozygotes = pronounced degradation from 35 days ΔNLSWld S heterozygotes = uninterrupted axons up to 35 days ΔNLSWld S homozygotes = uninterrupted axons up to 49 days Figure 4 Transmission electron microscopy Preservation of ultrastructure - ΔNLS Wld s mice have intact myelin sheaths, regularly spaced cytoskeleton and normal appearing mitochondria after 49 days Protective Wld S phenotype effective in young mice but is almost completely lost in older mice ΔNLSWld S phenotype shows stronger synaptic protection in young (100% intact NMJs 6 days after transection compared with ~50% in Wld S ) So will strong ΔNLSWld S protection of NMJ still be present in older mice?

12 Figure 5 Electrophysiology of mice aged 7.5 months (old), 6 days after sciatic nerve lesion A and B - amplitude of isometric force generated by nerve stimulation in ΔNLDWld S is ~50 times that of native Wld S C and D amplitude of the evoked EMG response in ΔNLDWld S is ~10 fold greater than native Wld S Native Wld S mice almost completely lose synaptic protection only weak or no contraction upon stimulation Robust contractions of ΔNLDWld S indistinguishable from nonaxotomised muscles Figure 5 Confocal imaging confirms loss of occupied NMJs in old Wld S native mice In NLS mice, 95% NMJ occupancy even in 12 month old mice Decline of synaptic protection with age is reduced when Wld S protein is extranuclear Dectection of Wld S protein variants in axons Wld S protein was found to be present in the axoplasm following axotomy, which supports a direct axonal role rather than an indirect nuclear role of Wld S Increased detection sensitivity showed presence of Wld S protein in native Wld S mice axons also suggest presence of extranuclear Wld S in axons (higher levels in NLS than native Wld S mice) and possibility of axonal transport of Wld S protein Wld S signal much stronger in NLS mice on both sides of a nerve crush suggests that ΔNLSWld S protein is transported both anterogradely and retrogradely More direct evidence needed to confirm this Figure 7 control The association of Wld S with organelles in subcellar fractionation of brain tissue and culture was studied Wld S and NLSWld S were present in mitochondria and microsomes (absent in WT). Similar data from rats and mice. ~85% of extracellular native/δnls Wld S was localised to mitochondria, although many mitochondria were Wld S free Figure 9 Superior cervical ganglion Blue stains nucleus Green stains Wld S protein Red stains mitochondria Merge shows the overlap In native Wld S mice, Wld S protein associated with nucleus In ΔNLSWld S mice, Wld S protein associated with mitochondria Same as above but with E.R

13 Summary graph Conclusions Wld S more effective when extranuclear Suggests cytoplasmic/direct axonal route of protein action Subcellular localisation to mitochondria and E.R (microsomes) Extracellular Wld S slows Wallerian degeneration axon survival extended from 4 to 7 weeks and decline of protection with age is significantly reduced Strong synaptic protection Need to investigate exact mechanisms further Shows there is non-nuclear medicated delay of Wallerian degeneration Conclusions ΔNLS Wld s transgenic mice considerably enhance axon and synapse protection Therefore ΔNLS Wld s transgenic mice should show more effective axon and synapse protection in neurodegenerative disease models BBQ What are the potential therapeutic implications of cytoplasmic Wld S fractionating with mitochondria and microsomes? Mitochondria require NAD+ to synthesis ATP and regulate cell signalling pathways Wld S overexpression of Nmnat1 increased NAD synthesis Therefore Wld S axons can maintain higher levels NAD+ and consequently ATP levels after axon lesion better than wild type axons Alternative mechanism = Nmnat blocks production of reactive oxygen species (ROS) from mitochondria Microsomes = fragmented E.R just stated that found Wld S protein in microsomes (restricted subdomains) didn t suggest any mechanism of action. Affects synthesis of proteins involved in axon protection? Implications = study has brought us closer to understanding protective Wld S mechanism although more research is need to know exact mechanisms that would be therapeutic targets Strengths/Weaknesses Strengths Very well illustrated Very thorough and convincing Use results from other studies to support their results well Created ΔNLS Wld s mouse and did sufficient tests to prove the phenotype is correct Positive step forward to finding a therapeutic for neurodegenerative diseases points to more effective therapeutic strategies based around Wld S Suggests what to investigate next after each of their conclusions Discusses what other studies have found with respect to Wld S mechanism Weaknesses Last few experiments of paper were not described very clearly Some of the imaging figures did not explain very well what the different stains were showing Inconsistent use of different lines of transgenic mice Small sample size only 2/3 mice of each different line/age Future Work Prove mechanism of Wld S in mitochondria, and investigate action of Wld S in E.R Address roles of NAD+ synthesis and VCP binding in axons and synapses Is the critical location of Wld S axonal or cytoplasmic? Can the enhanced protection offered by the ΔNLS Wld s variant be developed into more effective therapy for axonopathies? Can ΔNLS Wld s overcome the age dependent weakening of Wld s neuroprotection?

14 Axonal and neuromuscular synaptic phenotypes in Wlds, SOD1G93A and ostes mutant mice identified by fiber-optic confocal microendoscopy Wong et al 2009 Introduction Aims Methods Conclusions BBQ The future Introduction Discovery of neuroprotection in animal models is important for identifying new targets for treatment of disease Slow Wallerian degeneration in spontaneous mutant Wlds mice delays degeneration of distal axons This phenotype has no behavioural signs Current screening methods may not be effective in finding neuroprotective mutations Better methods need to be developed Aims Find genetic modifiers that would enhance synaptic protection in Wlds mice To find an effective method to recognize these phenodeviants which may have no behavioural signs To prove that CME and genomic mutagenesis can be combined to investigate neuromuscular pathology in vivo Methods Methods CME: Experimenters used a 1.5mm optical fiber probe to visualize the neuromuscular junctions ENU mutagenesis in BALB/c mice cross bred with thy1.2-yfp16/wlds double homozygotes Sciatic nerve cut at 1-2 months in F1 generation Outcome assessed 3 days later using CME 219 mice were screened in this way

15 CME can be used to distinguish between intact axons from those undergoing Wallerian degeneration ENU induces modifiers of axonal and synaptic degeneration in Wlds mice 7/219 mice showed variations in synaptic or axonal phenotype 2 of these phenodeviants (CEMOP_S2 and S5) showed the most protection Inheritance tests provide evidence that line CEMOP_S5 carries an autosomal-dominant, ENU induced mutation that delays synaptic degeneration Other lines also showed signs of inheritance but more tests will be needed CME can be used in longitudinal studies to monitor the degeneration of motor units Tests also carried out on SOD1 to prove that degeneration was not due to the CME method itself Show that CME can be used to detect and monitor pathological signs of spontaneous synaptic degeneration CME is also sensitive enough to monitor differences in peripheral nerve regeneration in ostes mice Successfully confirmed delayed axonal regeneration in homozygous and heterozygous ostes mice Conclusions Combining ENU mutagenesis with CME is an effective tool for studying the rate of synaptic degeneration and regeneration It identifies phenodeviants that are undetectable using conventional screening methods Ability to do longitudinal studies - gives evidence for potential diagnostic value

16 Conclusions CME has a lower spatial resolution than other methods However, it is faster, less invasive and more versatile A variant of the CME method may be suitable for longitudinal examination of NMJs in humans This could lead to more effective monitoring and treatment of neuromuscular disease Future studies Further developments of CME technology and identification of the mechanisms in mutants identified may be used for routine examination and monitoring of treatment from early stages in progression of neuromuscular disease Future studies Find beneficial modifier of early neuromuscular synaptic and axonal degeneration in SOD1G93A mutant mice The CME could be used to overcome the difficulties in studying SOD1G93A Big Burning Question What molecular effects does the CEMOP_S5 have and how do these suppress synaptic degeneration? Do they also affect axons? How would we find out? Could involve modification of transcription or translation of other genes Or by direct modification of intracellular signaling Or by targeting enzymic activity to intracellular compartments involved in energy metabolism Need to establish the gene mutations to identify mechanism of action Did not show protection of axons in this study but could repeat to check for axon protection Strengths Very convincing findings All in vivo Large sample size Easy to read and understand Backed up there findings with more experiments Summary ENU was used to induce genomic mutations in mice CME was then used to visualize the synaptic phenotypes in these mutant mice When combined these tools can be a powerful approach to investigation of neuromuscular pathology These findings may lead to better treatment of neuromuscular disease