**3. Spontaneous mutation models**

Since many years, several mouse models bearing spontaneous mutations leading to MN death have been identified: for instance, Wobbler (Duchen & Strich, 1968), Nmd (Cook et al., 1995), Pmn (Schmalbruch et al., 1991), Wasted (Newbery et al., 2005), Loa (Rogers et al., 2001) and Cra (Hrabe de Angelis et al., 2000) mice.

### **3.1 Wobbler mouse**

The Wobbler mouse mutation spontaneously occurred in the breeding stock of Falconer (1956) and was later mapped to the proximal mouse chromosome (Kaupmann et al., 1992)*.* It is the oldest known model of spontaneous MN disease, following a spontaneous recessive mutation in the wobbler (wr) gene, which encodes for the vacuolar-vesicular protein sorting 54 (Vps54) with a missense mutation L967Q. Vps54 mutation has been rarely described in ALS patients (Corrado et al., 2011). The protein is a subunit of the Golgi-associated retrograde protein (GARP) complex, used for fusion of endosome-derived transport vesicles to the trans-Golgi network. This model is considered a good model of MN degeneration, although the molecular mechanisms of the pathology in these mice are still unclear. Duchen and coll. (1968) showed that the progression of disease can be divided into three phases. i) The first, presymptomatic one, during the first 3 weeks after birth, ii) followed by the evolutionary one where the mice show alterations in motor behavior such as fine tremor of the head and slightly unsteady gait. iii) The third phase consists in the stabilization of the disease with the end of the neurodegenerative process. The progression of the disease is variable and leads to progressive denervation of skeletal muscles, determining muscle atrophy especially in the head, neck, shoulders and forelimbs. Limb muscles display different levels of atrophy: distally, atrophy is more severe than proximally, although in this model the hindlimbs are less severely affected. Moreover, there is a final progressive weight loss partially due to nutritional deprivation following muscle atrophy of the face and forelimbs (Boillee et al., 2003). Mice usually live up to 3-4 months, but sometimes the stabilization of the disease can delay their death for longer.

### **3.2 NMD mouse**

134 Amyotrophic Lateral Sclerosis

2000). The specific role of tau in the ALS pathogenesis remains unsettled, but the phenotypical and histological observations in P301L mutant mice suggests that it could be a

Studies on the vascular endothelial growth factor (VEGF) suggest a novel function for VEGF in the pathogenesis of MN degeneration. VEGF may be involved in spinal cord neuropathy mainly by affecting vascular growth or function. However, VEGF might also affect neural cells directly, but the *in vivo* relevance of such a mechanism has been poorly investigated. To study the potential role of VEGF in MN degeneration, Oosthuyse and coll. (2001) generated a 'knock-in' mouse, in which the hypoxia-response element sequence in the Vegf promoter was deleted. Vegf -/- mice appear healthy until 5 months of age, when they develop symptoms of MN disease, i.e. severe adult-onset muscle weakness due to degeneration of lower MNs, reminiscent of the clinical symptoms and neuropathological signs of ALS. Similarly, VEGF replacement has beneficial effects in SOD1 G93A mice (Lunn et al., 2009). These findings indicate that reduced neural perfusion and maybe also insufficient VEGF-

Since many years, several mouse models bearing spontaneous mutations leading to MN death have been identified: for instance, Wobbler (Duchen & Strich, 1968), Nmd (Cook et al., 1995), Pmn (Schmalbruch et al., 1991), Wasted (Newbery et al., 2005), Loa (Rogers et al.,

The Wobbler mouse mutation spontaneously occurred in the breeding stock of Falconer (1956) and was later mapped to the proximal mouse chromosome (Kaupmann et al., 1992)*.* It is the oldest known model of spontaneous MN disease, following a spontaneous recessive mutation in the wobbler (wr) gene, which encodes for the vacuolar-vesicular protein sorting 54 (Vps54) with a missense mutation L967Q. Vps54 mutation has been rarely described in ALS patients (Corrado et al., 2011). The protein is a subunit of the Golgi-associated retrograde protein (GARP) complex, used for fusion of endosome-derived transport vesicles to the trans-Golgi network. This model is considered a good model of MN degeneration, although the molecular mechanisms of the pathology in these mice are still unclear. Duchen and coll. (1968) showed that the progression of disease can be divided into three phases. i) The first, presymptomatic one, during the first 3 weeks after birth, ii) followed by the evolutionary one where the mice show alterations in motor behavior such as fine tremor of the head and slightly unsteady gait. iii) The third phase consists in the stabilization of the disease with the end of the neurodegenerative process. The progression of the disease is variable and leads to progressive denervation of skeletal muscles, determining muscle atrophy especially in the head, neck, shoulders and forelimbs. Limb muscles display different levels of atrophy: distally, atrophy is more severe than proximally, although in this model the hindlimbs are less severely affected. Moreover, there is a final progressive weight loss partially due to nutritional deprivation following muscle atrophy of the face and forelimbs (Boillee et al., 2003). Mice usually live up to 3-4 months, but sometimes the stabilization of the disease can delay their death for longer.

dependent neuroprotection cause MN degeneration (Oosthuyse et al., 2001).

key molecule in neurodegeneration occurring in ALS.

**3. Spontaneous mutation models** 

**3.1 Wobbler mouse** 

2001) and Cra (Hrabe de Angelis et al., 2000) mice.

**2.2.4 VEGF** 

Cox and coll. (1998) identified mice carrying 2 independent mutations in the neuromuscular degeneration (Nmd) gene on two alleles: nmdj and nmd2j, leading to a progressive degeneration of spinal MNs and muscular atrophy. The nmd gene produces a ubiquitously expressed DNA helicase/ATPase protein previously described as immunoglobulin S-mu binding protein-2 (Smbp2; Fukita et al., 1993), glial factor 1 (Gf1; Kerr & Khalili, 1991), rat insulin enhancer binding protein 1 (rip1; Shieh et al., 1995) and cardiac transcription factor 1 (Catf1; Sebastiani et al., 1995).

Mutant mice are characterized by a progressive paralysis that initially begins with the hindlimbs. The forelimbs are affected to a variable degree with paralysis, generally evident only toward the latest stages of the disease. Homozygous Nmd mutants can be easily distinguished from their littermate controls at 2 weeks of age by their dorsally contracted hindlimbs and impaired movement. Affected mice rarely survive beyond 4 weeks of age, but the exact cause of death is unclear.
