Wobbler, a mutation affecting motoneuron survival and gonadal functions in the mouse, maps to proximal chromosome 11

The usage and advantages of several common amyotrophic lateral sclerosis animal models

Amyotrophic lateral sclerosis is a fatal, multigenic, multifactorial neurodegenerative disease characterized by upper and lower motor neuron loss. Animal models are essential for investigating pathogenesis and reflecting clinical manifestations, particularly in developing reasonable prevention and therapeutic methods for human diseases. Over the decades, researchers have established a host of different animal models in order to dissect amyotrophic lateral sclerosis (ALS), such as yeast, worms, flies, zebrafish, mice, rats, pigs, dogs, and more recently, non-human primates. Although these models show different peculiarities, they are all useful and complementary to dissect the pathological mechanisms of motor neuron degeneration in ALS, contributing to the development of new promising therapeutics. In this review, we describe several common animal models in ALS, classified by the naturally occurring and experimentally induced, pointing out their features in modeling, the onset and progression of the pathology, and their specific pathological hallmarks. Moreover, we highlight the pros and cons aimed at helping the researcher select the most appropriate among those common experimental animal models when designing a preclinical ALS study.

Role of GARP Vesicle Tethering Complex in Golgi Physiology

The Golgi associated retrograde protein complex (GARP) is an evolutionarily conserved component of Golgi membrane trafficking machinery that belongs to the Complexes Associated with Tethering Containing Helical Rods (CATCHR) family. Like other multisubunit tethering complexes such as COG, Dsl1, and Exocyst, the GARP is believed to function by tethering and promoting fusion of the endosome-derived small trafficking intermediate. However, even twenty years after its discovery, the exact structure and the functions of GARP are still an enigma. Recent studies revealed novel roles for GARP in Golgi physiology and identified human patients with mutations in GARP subunits. In this review, we summarized our knowledge of the structure of the GARP complex, its protein partners, GARP functions related to Golgi physiology, as well as cellular defects associated with the dysfunction of GARP subunits.

Childhood spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by biallelic mutations in the SMN1 (survival motor neuron 1) gene on chromosome 5q13.2, which leads to a progressive degeneration of alpha motor neurons in the spinal cord and in motor nerve nuclei in the caudal brainstem. It is characterized by progressive proximally accentuated muscle weakness with loss of already acquired motor skills, areflexia and, depending on the phenotype, varying degrees of weakness of the respiratory and bulbar muscles. Over the past decade, disease-modifying therapies have become available based on splicing modulation of the SMN2 with SMN1 gene replacement, which if initiated significantly modifies the natural course of the disease. Newborn screening for SMA has been implemented in an increasing number of centers; however, available evidence for these new treatments is often limited to a small spectrum of patients concerning age and disease stage.

ROS scavengers decrease γH2ax spots in motor neuronal nuclei of ALS model mice in vitro

Background: Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease characterized by the loss of motor neurons in cerebral cortex, brainstem and spinal cord. Numerous studies have demonstrated signs of oxidative stress in postmortem neuronal tissue, cerebrospinal fluid, plasma and urine of ALS patients, without focusing on the specific processes within motor neurons. Thus, we aimed to investigate the relevance of reactive oxygen species (ROS) detoxification mechanisms and its consequences on the formation of toxic/lethal DNA double strand breaks (DSBs) in the ALS model of the Wobbler mouse.

Methods: Live cell imaging in dissociated motor neuronal cultures was used to investigate the production of ROS using Dihydroethidium (DHE). The expression levels of ROS detoxifying molecules were investigated by qPCR as well as Western blots. Furthermore, the expression levels of DNA damage response proteins p53bp1 and H2ax were investigated using qPCR and immunofluorescence staining. Proof-of-principle experiments using ROS scavengers were performed in vitro to decipher the influence of ROS on the formation of DNA double strand breaks quantifying the γH2ax spots formation.

Results: Here, we verified an elevated ROS-level in spinal motor neurons of symptomatic Wobbler mice in vitro. As a result, an increased number of DNA damage response proteins p53bp1 and γH2ax in dissociated motor neurons of the spinal cord of Wobbler mice was observed. Furthermore, we found a significantly altered expression of several antioxidant molecules in the spinal cord of Wobbler mice, suggesting a deficit in ROS detoxification mechanisms. This hypothesis could be verified by using ROS scavenger molecules in vitro to reduce the number of γH2ax foci in dissociated motor neurons and thus counteract the harmful effects of ROS.

Conclusion: Our data indicate that maintenance of redox homeostasis may play a key role in the therapy of the neurodegenerative disease ALS. Our results underline a necessity for multimodal treatment approaches to prolong the average lifespan of motor neurons and thus slow down the progression of the disease, since a focused intervention in one pathomechanism seems to be insufficient in ALS therapy.

The Spatiotemporal Pattern of Degeneration in the Cerebellum of the Wobbler Mouse

Amyotrophic lateral sclerosis (ALS) is a common neurodegenerative disease that affects motor neurons in the spinal cord and motor cortex. Various mouse models have been used to investigate the progression of the pathology of sporadic and familial ALS. Degeneration in the spinal cord and motor cortex in the Wobbler mouse model of sporadic ALS have been documented, but alterations of the cerebellum during disease progression have not been well characterized. We analyzed neurodegeneration and inflammatory responses in the cerebellar cortex of preclinical (p20), clinical (p40), and late (p60) stages in these mice. We did not identify evidence of neuron cell death, but we observed an inflammatory response detected by IL1B and TNFA expression by quantitative PCR, increased activated microglia and astrocytosis by immunohistochemistry, and ultrastructural abnormalities in the cerebella of Wobbler mice at late stages. These alterations may be caused by protein aggregations and variations in the distribution of cytoskeletal proteins; they might be reflected in the early manifestation of head tremor, which precedes motor deficits in these mice. Thus, we conclude that, in addition to the motor cortex and spinal cord, the cerebellum is affected by neurodegenerative and inflammatory processes in the Wobbler mouse model of ALS.

Inflammation and neuronal death in the motor cortex of the wobbler mouse, an ALS animal model

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder of the upper and lower motor neurons, characterized by rapid progressive weakness, muscle atrophy, dysarthria, dysphagia, and dyspnea. Whereas the exact cause of ALS remains uncertain, the wobbler mouse (phenotype WR; genotype wr/wr) equally develops a progressive degeneration of motor neurons in the spinal cord and motor cortex with striking similarities to sporadic human ALS, suggesting the possibility of a common pathway to cell death.

METHODS

With the aid of immunohistochemistry, confocal laser scanning microscopy, and transmission electron microscopy techniques, we analyze the proliferation behavior of microglial cells and astrocytes. We also investigate possible motor neuron death in the mouse motor cortex at different stages of the wobbler disease, which so far has not received much attention.

RESULTS

An abnormal density of Iba-1-positive microglial cells expressing pro-inflammatory tumor necrosis factor (TNF) alpha- and glial fibrillary acidic protein (GFAP)-positive activated astroglial cells was detected in the motor cortex region of the WR mouse 40 days postnatal (d.p.n.). Motor neurons in the same area show caspase 3 activation indicating neurodegenerative processes, which may cause progressive paralysis of the WR mice. It could also cause cell degeneration, such as vacuolization, dilation of the ER, and swollen mitochondria at the same time, and support the assumption that inflammation might be an important contributing factor of motor neuron degeneration. This would appear to be confirmed by the fact that there was no conspicuous increase of microglial cells and astrocytes in the motor cortex of control mice at any time.

CONCLUSIONS

Activated microglial cells secrete a variety of pro-inflammatory and neurotoxic factors, such as TNF alpha, which could initiate apoptotic processes in the affected wobbler motor neurons, as reflected by caspase 3 activation, and thus, the neuroinflammatory processes might influence or exacerbate the neurodegeneration. Although it remains to be clarified whether the immune response is primary or secondary and how harmful or beneficial it is in the WR motor neuron disease, anti-inflammatory treatment might be considered.

VPS54 and the wobbler mouse

The wobbler mouse is an animal model for human motor neuron disease, such as amyotrophic lateral sclerosis (ALS). The spontaneous, recessive wobbler mutation causes degeneration of upper and lower motor neurons leading to progressive muscle weakness with striking similarities to the ALS pathology. The wobbler mutation is a point mutation affecting Vps54, a component of the Golgi-associated retrograde protein (GARP) complex. The GARP complex is a ubiquitously expressed Golgi-localized vesicle tethering complex, tethering endosome-derived vesicles to the trans Golgi network. The wobbler point mutation leads to a destabilization of the Vps54 protein and thereby the whole GARP complex. This effectuates impairments of the retrograde vesicle transport, mis-sorting of Golgi- and endosome localized proteins and on the long run defects in Golgi morphology and function. It is currently largely unknown how the destabilization of the GARP complex interferes with the pathological hallmarks, reported for the wobbler motor neuron degeneration, like neurofilament aggregation, axonal transport defects, hyperexcitability, mitochondrial dysfunction, and how these finally lead to motor neuron death. However, the impairments of the retrograde vesicle transport and the Golgi-function appear to be critical phenomena in the molecular pathology of the wobbler motor neuron disease.

Implementation of a manual for working with wobbler mice and criteria for discontinuation of the experiment

Mouse breeding is of importance to a whole range of medical and biological research. There are many known mouse models for motor neuron diseases. However, it must be kept in mind that especially mouse models for amyotrophic lateral sclerosis develop severe symptoms causing intense stress. This article is designed to summarize conscientious work with the wobbler mouse, a model for the sporadic form of amyotrophic lateral sclerosis. This mouse model is characterized by a degeneration of α-motor-neurons leading to head tremor, loss of body weight and rapidly progressive paralysis. Although this mouse model has been known since 1956, there are no guidelines for breeding wobbler mice. Due to the lack of such guidelines the present study tries to close this gap and implements a manual for further studies. It includes the whole workflow in regard to wobbler mice from breeding and animal care taking, genotyping and phenotype analysis, but also gives some examples for the use of various neuronal tissues for histological investigation. Beside the progress in research a second aim should always be the enhancement of mouse welfare and reduction of stress for the laboratory animals.

Neuroprotective effects of the Sigma-1 receptor (S1R) agonist PRE-084, in a mouse model of motor neuron disease not linked to SOD1 mutation

The identification of novel molecular targets crucially involved in motor neuron degeneration/survival is a necessary step for the development of hopefully more effective therapeutic strategies for amyotrophic lateral sclerosis (ALS) patients. In this view, S1R, an endoplasmic reticulum (ER)-resident receptor with chaperone-like activity, has recently attracted great interest. S1R is involved in several processes leading to acute and chronic neurodegeneration, including ALS pathology. Treatment with the S1R agonist PRE-084 improves locomotor function and motor neuron survival in presymptomatic and early symptomatic mutant SOD1-G93A ALS mice. Here, we tested the efficacy of PRE-084 in a model of spontaneous motor neuron degeneration, the wobbler mouse (wr) as a proof of concept that S1R may be regarded as a key therapeutic target also for ALS cases not linked to SOD1 mutation. Increased staining for S1R was detectable in morphologically spared cervical spinal cord motor neurons of wr mice both at early (6th week) and late (12th week) phases of clinical progression. S1R signal was also detectable in hypertrophic astrocytes and reactive microglia of wr mice. Chronic treatment with PRE-084 (three times a week, for 8weeks), starting at symptom onset, significantly increased the levels of BDNF in the gray matter, improved motor neuron survival and ameliorated paw abnormality and grip strength performance. In addition, the treatment significantly reduced the number of reactive astrocytes whereas, that of CD11b+ microglial cells was increased. A deeper evaluation of microglial markers revealed significant increased number of cells positive for the pan-macrophage marker CD68 and of CD206+ cells, involved in tissue restoration, in the white matter of PRE-084-treated mice. The mRNA levels of TNF-α and IL-1β were not affected by PRE-084 treatment. Thus, our results support pharmacological manipulation of S1R as a promising strategy to cure ALS and point to increased availability of growth factors and modulation of astrocytosis and of macrophage/microglia as part of the mechanisms involved in S1R-mediated neuroprotection.

The wobbler mouse, an ALS animal model

This review article is focused on the research progress made utilizing the wobbler mouse as animal model for human motor neuron diseases, especially the amyotrophic lateral sclerosis (ALS). The wobbler mouse develops progressive degeneration of upper and lower motor neurons and shows striking similarities to ALS. The cellular effects of the wobbler mutation, cellular transport defects, neurofilament aggregation, neuronal hyperexcitability and neuroinflammation closely resemble human ALS. Now, 57 years after the first report on the wobbler mouse we summarize the progress made in understanding the disease mechanism and testing various therapeutic approaches and discuss the relevance of these advances for human ALS. The identification of the causative mutation linking the wobbler mutation to a vesicle transport factor and the research focussed on the cellular basis and the therapeutic treatment of the wobbler motor neuron degeneration has shed new light on the molecular pathology of the disease and might contribute to the understanding the complexity of ALS.

Endosomal accumulation of APP in wobbler motor neurons reflects impaired vesicle trafficking: implications for human motor neuron disease

Background

The cause of sporadic amyotrophic lateral sclerosis (ALS) is largely unknown but hypotheses about disease mechanisms include oxidative stress, defective axonal transport, mitochondrial dysfunction and disrupted RNA processing. Whereas familial ALS is well represented by transgenic mutant SOD1 mouse models, the mouse mutant wobbler (WR) develops progressive motor neuron degeneration due to a point mutation in the Vps54 gene, and provides an animal model for sporadic ALS. VPS54 protein as a component of a protein complex is involved in vesicular Golgi trafficking; impaired vesicle trafficking might also be mechanistic in the pathogenesis of human ALS.

Results

In motor neurons of homozygous symptomatic WR mice, a massive number of endosomal vesicles significantly enlarged (up to 3 μm in diameter) were subjected to ultrastructural analysis and immunohistochemistry for the endosome-specific small GTPase protein Rab7 and for amyloid precursor protein (APP). Enlarged vesicles were neither detected in heterozygous WR nor in transgenic SOD1(G93A) mice; in WR motor neurons, numerous APP/Rab7-positive vesicles were observed which were mostly LC3-negative, suggesting they are not autophagosomes.

Conclusions

We conclude that endosomal APP/Rab7 staining reflects impaired vesicle trafficking in WR mouse motor neurons. Based on these findings human ALS tissues were analysed for APP in enlarged vesicles and were detected in spinal cord motor neurons in six out of fourteen sporadic ALS cases. These enlarged vesicles were not detected in any of the familial ALS cases. Thus our study provides the first evidence for wobbler-like aetiologies in human ALS and suggests that the genes encoding proteins involved in vesicle trafficking should be screened for pathogenic mutations.

Genetic rodent models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective death of motor neurons in the motor cortex, brainstem, and spinal cord. A large number of rodent models are available that show motor neuron death and a progressive motor phenotype that is more or less reminiscent of what occurs in patients. These rodent models contain genes with spontaneous or induced mutations or (over) express different (mutant) genes. Some of these models have been of great value to delineate potential pathogenic mechanisms that cause and/or modulate selective motor neuron degeneration. In addition, these genetic rodent models play a crucial role in testing and selecting potential therapeutics that can be used to treat ALS and/or other motor neuron disorders. In this paper, we give a systematic overview of the most important genetic rodent models that show motor neuron degeneration and/or develop a motor phenotype. In addition, we discuss the value and limitations of the different models and conclude that it remains a challenge to find more and better rodent models based on mutations in new genes causing ALS.

Tumor necrosis factor-alpha (TNF-alpha) regulates shedding of TNF-alpha receptor 1 by the metalloprotease-disintegrin ADAM8: evidence for a protease-regulated feedback loop in neuroprotection

Tumor necrosis factor alpha (TNF-alpha) is a potent cytokine in neurodegenerative disorders, but its precise role in particular brain disorders is ambiguous. In motor neuron (MN) disease of the mouse, exemplified by the model wobbler (WR), TNF-alpha causes upregulation of the metalloprotease-disintegrin ADAM8 (A8) in affected brain regions, spinal cord, and brainstem. The functional role of A8 during MN degeneration in the wobbler CNS was investigated by crossing WR with A8-deficient mice: a severely aggravated neuropathology was observed for A8-deficient WR compared with WR A8(+/-) mice, judged by drastically reduced survival [7 vs 81% survival at postnatal day 50 (P50)], accelerated force loss in the forelimbs, and terminal akinesis. In vitro protease assays using soluble A8 indicated specific cleavage of a TNF-alpha receptor 1 (p55 TNF-R1) but not a TNF-R2 peptide. Cleavage of TNF-R1 was confirmed in situ, because levels of soluble TNF-R1 were increased in spinal cords of standard WR compared with wild-type mice but not in A8-deficient WR mice. In isolated primary neurons and microglia, TNF-alpha-induced TNF-R1 shedding was dependent on the A8 gene dosage. Furthermore, exogenous TNF-alpha showed higher toxicity for cultured neurons from A8-deficient than for those from wild-type mice, demonstrating that TNF-R1 shedding by A8 is neuroprotective. Our results indicate an essential role for ADAM8 in modulating TNF-alpha signaling in CNS diseases: a feedback loop integrating TNF-alpha, ADAM8, and TNF-R1 shedding as a plausible mechanism for TNF-alpha mediated neuroprotection in situ and a rationale for therapeutic intervention.

Experimental models for the study of neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of unknown cause, characterized by the selective and progressive death of both upper and lower motoneurons, leading to a progressive paralysis. Experimental animal models of the disease may provide knowledge of the pathophysiological mechanisms and allow the design and testing of therapeutic strategies, provided that they mimic as close as possible the symptoms and temporal progression of the human disease. The principal hypotheses proposed to explain the mechanisms of motoneuron degeneration have been studied mostly in models in vitro, such as primary cultures of fetal motoneurons, organotypic cultures of spinal cord sections from postnatal rodents and the motoneuron-like hybridoma cell line NSC-34. However, these models are flawed in the sense that they do not allow a direct correlation between motoneuron death and its physical consequences like paralysis. In vivo, the most widely used model is the transgenic mouse that bears a human mutant superoxide dismutase 1, the only known cause of ALS. The major disadvantage of this model is that it represents about 2%-3% of human ALS. In addition, there is a growing concern on the accuracy of these transgenic models and the extrapolations of the findings made in these animals to the clinics. Models of spontaneous motoneuron disease, like the wobbler and pmn mice, have been used aiming to understand the basic cellular mechanisms of motoneuron diseases, but these abnormalities are probably different from those occurring in ALS. Therefore, the design and testing of in vivo models of sporadic ALS, which accounts for >90% of the disease, is necessary. The main models of this type are based on the excitotoxic death of spinal motoneurons and might be useful even when there is no definitive demonstration that excitotoxicity is a cause of human ALS. Despite their difficulties, these models offer the best possibility to establish valid correlations between cellular alterations and motor behavior, although improvements are still necessary in order to produce a reliable and integrative model that accurately reproduces the cellular mechanisms of motoneuron degeneration in ALS.

Cell death pathways differ in several mouse models with motoneurone disease: analysis of pure motoneurone populations at a presymptomatic age

To identify candidate genes that are responsible for motoneurone degeneration, we combined laser capture microdissection with microarray technology. We analysed gene expression in pure motoneurones from two mouse mutants that develop motoneurone degeneration, progressive motor neuronopathy and wobbler. At a presymptomatic age, there was a significant differential expression of a restricted number of genes (25 and 72 in progressive motor neuronopathy and wobbler respectively, of 22 600 transcripts screened). We compared these results to our previous analyses in the copper-zinc superoxide dismutase mutant mouse (SOD1(G93A)) in which we observed a de-regulation of 27 genes. Some of these genes were de-regulated uniquely in one mouse mutant and some have already been identified in cell death pathways implicated in amyotrophic lateral sclerosis and animal models of motoneurone degeneration (i.e. de-regulation of intermediate filaments, axonal transport, the ubiquitin-proteasome system and excitotoxicity). One gene, vimentin, was differentially up-regulated in all mouse mutants; this main candidate gene has been confirmed by in situ hybridization and immunohistochemistry to be expressed in motoneurones in all mouse mutants. Furthermore, vimentin expression correlated with the state of motoneurone degeneration. These results identify early molecular changes that may be involved in the pathogenesis of motoneurones leading to cell death and favour a complex multipathway induction of the disease; surprisingly, there was no important modification in cell death-associated genes. This is the first study to show a clear difference in the genes that are de-regulated at an early stage in three different mouse models of motoneurone disease.

Mutation of Vps54 causes motor neuron disease and defective spermiogenesis in the wobbler mouse

Vacuolar-vesicular protein sorting (Vps) factors are involved in vesicular trafficking in eukaryotic cells. We identified the missense mutation L967Q in Vps54 in the wobbler mouse, an animal model of amyotrophic lateral sclerosis, and also characterized a lethal allele, Vps54(beta-geo). Motoneuron survival and spermiogenesis are severely compromised in the wobbler mouse, indicating that Vps54 has an essential role in these processes.

Progesterone restores retrograde labeling of cervical motoneurons in Wobbler mouse motoneuron disease

The Wobbler mouse, a mutant characterized by motoneuron degeneration in the cervical spinal cord, has been used to test the efficacy of novel treatments for human motoneuron diseases (HMD). Previous reports have shown that slow axonal transport is impaired in Wobblers and other models of HMD. Since progesterone (PROG) corrects some morphological, molecular, and functional abnormalities of Wobbler mice, we studied if steroid exposure for 8 weeks restored retrograde axonal transport by measuring motoneuron labeling after injection of fluorogold into the limb muscles. The dye was injected into forelimb biceps bracchii and flexor or into the rearlimb gastrocnemius muscles; 6 days later, the number of fluorescent motoneurons and the total number of cresyl violet stained motoneurons were counted in the cervical (C5-T1) or lumbar (L3-L5) spinal cord regions. A pronounced reduction (- 42.2%) of the percent of fluorescent motoneurons in Wobbler mice cervical cord was noted, which was significantly corrected after PROG treatment. In contrast, labeling of lumbar motoneurons was not reduced in Wobbler mice and was not affected by PROG treatment. In no case PROG showed an effect in control mice. Concomitantly, PROG slightly but significantly increased biceps weight of Wobbler mice. Behaviorally, PROG-treated Wobblers performed better on a motor test (hanging time from a horizontal rope) compared to untreated counterparts. We postulate a dual role for PROG in the Wobbler mouse, in part by prevention of motoneuron degeneration and also by enhancement of axonal transport. The latter mechanism could improve the traffic of neurotrophic factors from the forelimb muscles into the ailing motoneurons, improving neuromuscular function in this murine model of HMD.

Evidence for chronic mitochondrial impairment in the cervical spinal cord of a murine model of motor neuron disease

Profound alteration of the oxygen consumption rate (QO2) is present in the cervical spinal cord (CS) of the wobbler mice aged 12 weeks (wr12). Early symptomatic mice at 4 weeks (wr4) show less pronounced changes with decreases of basal QO2 (P < 0.03) and of QO2 through complex I (P < 0.04). Mitochondrial respiratory enzyme activities, measured spectrophotometrically in the CS homogenate, show no difference between wr12 and controls, whereas complex I is reduced in the wr4 CS (P < 0.0003). Complex I activity is lower than normal both in wr12 and wr4 CS when measured in motor neurons by mean of a histochemical technique. Electron microscopy (EM) reveals a mixture of normal and morphologically altered mitochondria in wr4 motor neurons. The wobbler lumbar spinal cord is spared even at 12 weeks. Our results demonstrate the presence of mitochondrial abnormalities in the wobbler CS since the first manifestations of the disease. Thus, chronic mitochondrial dysfunction has a contributory role in motor neuron degeneration in the wobbler disease.

Basis of progesterone protection in spinal cord neurodegeneration

Progesterone neuroprotection has been reported in experimental brain, peripheral nerve and spinal cord injury. To investigate for a similar role in neurodegeneration, we studied progesterone effects in the Wobbler mouse, a mutant presenting severe motoneuron degeneration and astrogliosis of the spinal cord. Implant of a single progesterone pellet (20 mg) during 15 days produced substantial changes in Wobbler mice spinal cord. Morphologically, motoneurons of untreated Wobbler mice showed severe vacuolation of intracellular organelles including mitochondria. In contrast, neuropathology was less pronounced in Wobbler mice receiving progesterone, together with a reduction of vacuolated cells and preservation of mitochondrial ultrastructure. Determination of mRNAs for the alpha 3 and beta 1 subunits of neuronal Na, K-ATPase, showed that mRNA levels in untreated mice were significantly reduced, whereas progesterone therapy re-established the expression of both subunits. Additionally, progesterone treatment of Wobbler mice attenuated the aberrant expression of the growth-associated protein (GAP-43) mRNA which otherwise occurred in motoneurons of untreated animals. The hormone, however, was without effect on astrocytosis of Wobbler mice, determined by glial fibrillary acidic protein (GFAP)-immunostaining. Lastly, progesterone treatment of Wobbler mice enhanced grip strength and prolonged survival at the end of the 15-day observation period. Recovery of morphology and molecular motoneuron parameters of Wobbler mice receiving progesterone, suggest a new and important role for this hormone in the prevention of spinal cord neurodegenerative disorders.

Comparative transcription map of the wobbler critical region on mouse chromosome 11 and the homologous region on human chromosome 2p13-14

BACKGROUND

To support the positional cloning of the mouse mutation wobbler (wr) the corresponding regions on human Chr2p13-14 and mouse Chr11 were analyzed in detail and compared with respect to gene content, order, and orientation.

RESULTS

The gene content of the investigated regions was highly conserved between the two species: 20 orthologous genes were identified on our BAC/YAC contig comprising 4.5 Mb between REL/Rel and RAB1A/Rab1a. Exceptions were pseudogenes ELP and PX19 whose mouse counterparts were not located within the analyzed region. Two independently isolated genomic clones indicate an inversion between man and mouse with the inverted segment being identical to the wobbler critical interval. We investigated the wobbler critical region by extensive STS/EST mapping and genomic sequencing. Additionally, the full-length cDNA sequences of four newly mapped genes as well as the previously mapped gene Otx1 were established and subjected to mutation analysis. Our data indicate that all genes in the wr critical region have been identified.

CONCLUSION

Unexpectedly, neither mutation analysis of cDNAs nor levels of mRNAs indicated which of the candidate genes might be affected by the wr mutation. The possibility arises that there might be hitherto unknown effects of mutations, in addition to structural changes of the mRNA or regulatory abnormalities.

Mouse sperm cell-specific DnaJ first homologue: an evolutionarily conserved protein for spermiogenesis

Msj-1 (mouse sperm cell-specific DnaJ first homologue) is a gene specifically expressed in germ cells at haploid stages. The protein first appears in round spermatids, accumulates in the periacrosomal region of elongating spermatids, and is maintained in spermatozoa. The msj-1 expression pattern is consistent with a role for this DnaJ protein in the spermiogenesis process. In this study, we used two experimental models, the anuran amphibian Rana esculenta and the wobbler mutant mouse, to explore the role of MSJ-1 during spermatogenesis, with a focus on spermiogenesis. Mice homozygous for the recessive mutation wobbler (wr/wr), a mutation of unknown identity, produce sperm cells characterized by a missing acrosome. In Rana esculenta testis, detection of high levels of MSJ-1 protein coincided with the appearance of postmeiotic germ cells during the annual sexual cycle. Conversely, elimination of the meiotic and postmeiotic stages, through gonadotropin administration at low temperature, abolished the MSJ-1 immunoreactive signal. In 20-day-old mice, when postmeiotic germ cells appeared for the first time, MSJ-1 mRNA and protein were observed in +/+ testis but were barely detectable in wr/wr testis. In adult testis, reduced MSJ-1 protein levels were observed in both +/wr and wr/wr testis, as compared with +/+ controls. Similarly, numbers of spermatids that stained by immunofluorescence for MSJ-1 appeared to be progressively reduced in adult +/+, +/wr, and wr/wr mouse testes, respectively. Characterization of the endocrine status of wobbler testis revealed reduced transcript levels of estrogen receptor alpha and reduced intratesticular androgen levels. However, androgen treatment did not affect MSJ-1 protein levels in either frogs or mice. In conclusion, our data in Rana esculenta and the wobbler mouse demonstrate a tight correlation between MSJ-1 protein expression and postmeiotic stages. In particular, the findings in the wobbler testis suggest a role for this protein in acrosomogenesis.

Genetic modifiers that aggravate the neurological phenotype of the wobbler mouse

The autosomal recessive mutation wobbler of the mouse (phenotype WR; genotype wr/wr) causes muscular atrophy due to motoneuron degeneration with 100% penetrance on the standard Mus musculus laboratorius C57BL/6J background. In inter- and backcrosses with M. m. castaneus strain CAST/EI we have observed a variability in the severity of neurological symptoms. Approximately 15% of the WR (wr/wr) CAST/B6 hybrids were modified wobbler (WR*) mice defined by an aggravated neuromuscular phenotype with hindlimbs severely affected in addition to forelimbs. Histologically the overt WR* phenotype was paralleled by a caudally extended neurodegeneration in the ventral horn of the spinal cord with severe astrogliosis, and levels of acetylcholine receptor alpha-subunit mRNA in leg muscle much higher than in standard WR mice. Segregation analysis, using 68 polymorphic autosomal markers in a whole genome scan, revealed a major modifier gene locus, termed wrmod1, on chromosome 14. Individual recombination events in chromosome 14 consomic mice narrowed the wrmod1 candidate region to a 29 cM interval between D14MIT154 and D14MIT105, a region homologous to human chromosome 13q. Our analysis provides access to genes that modify neurodegeneration, the human counterparts of which may be responsible for the variable expression of hereditary spinal muscular atrophies.

Specific features of chronic astrocyte gliosis after experimental central nervous system (CNS) xenografting and in Wobbler neurological mutant CNS

This study sets out to compare and contrast the astrocyte reaction in two unrelated experimental designs both resulting in marked chronic astrogliosis and natural motoneuron death in the wobbler mutant mouse and brain damage in the context of transplantation of xenogeneic embryonic CNS tissue into the striatum of newborn mice. The combined use of GFAP-labeling and confocal imaging allows the morphological comparison between these two different types of astrogliosis. Our findings demonstrate that, in mice, after tissue transplantation in the striatum, gliosis is not restricted to the regions of damage: it occurs not only near the site of transplantation, the striatum, but also in more distant regions of the CNS and particularly in the spinal cord. In the wobbler mutant mouse, a strong gliosis is observed in the spinal cord, site of motoneuronal cell loss. However, moderate astrocytic reaction (increased GFAP-immunoreactivity) can also be found in other wobbler CNS regions, remote from the spinal cord. In the wobbler ventral horn, where neurons degenerate, the hypertrophied reactive astrocytes exhibit a dramatic increase of glial fibrils and surround the motoneuron cell bodies, occupying most of the motoneuron environment. The striking and specific presence of hypertrophic astrocytes in wobbler mice accompanied by a dramatic increase of glial fibrils located in the vicinity of motoneuron cell bodies suggests that short astrogliosis fills the space left by degenerating motoneurons and interferes with their survival. In the spinal cord of xenografted mice, chronic astrogliosis is also observed, but only glial processes without hypertrophied cell bodies are found in the neuronal micro-environment. It is tempting to speculate that gliosis in the wobbler spinal cord, the local accumulation of astrocyte cell bodies, and high density of astrocytic processes may interfere with the diffusion of neuroactive substances in gliotic tissue, some of which are neurotoxic, and cooperate or even trigger neuronal death.

Transient massive DNA fragmentation in nervous system during the early course of a murine neurodegenerative disease

In neurodegenerative diseases, such as Alzheimer's disease or HIV encephalitis, neuronal DNA fragmentation has been observed at unexpected high frequencies, without definitive evidence for activation of an irreversible apoptotic pathway. The wobbler mouse is a suggested genetic model of neurodegenerative disease. The mutant mouse develops normally until the fourth week of age when atrophy and weakness of forelimb muscles become apparent. There is a slow progression of the disease and wobbler mice may survive for several months. Spinal cord examination reveals the presence of several motoneurons with perikaryal vacuolar degeneration. In this study, we observed, using terminal dUTP nick-end-labelling staining in mutant spinal cord sections, a massive although very transient DNA fragmentation in different cell types, including glial cells and motoneurons, before the apparition of any clinical symptoms. In older wobbler mice, this DNA fragmentation had completely disappeared and the majority of motoneurons survived. To our knowledge, this is the first example of a massive and transient DNA fragmentation in the central nervous system during the early course of a neurodegenerative disease.

Cellular basis of steroid neuroprotection in the wobbler mouse, a genetic model of motoneuron disease

1. The Wobbler mouse suffers an autosomal recessive mutation producing severe motoneuron degeneration and astrogliosis in the spinal cord. It has been considered a suitable model of human motoneuron disease, including the sporadic form of amyotrophic lateral sclerosis (ALS). 2. Evidences exist demonstrating increased oxidative stress in the spinal cord of Wobbler mice, whereas antioxidant therapy delayed neurodegeneration and improved muscle trophism. 21-Aminosteroids are glucocorticoid-derived hydrophobic compounds with antioxidant potency 3 times higher than vitamin E and 100 times higher than methylprednisolone. They do not bind to intracellular receptors, and prevent lipid peroxidation by insertion into membrane lipid bilayers. 3. In common with the spinal cord of ALS patients, Wobbler mice present astrocytosis with hyperexpression of glial fibrillary acidic protein (GFAP), and increased expression of nitric oxide synthase (NOS) and growth-associated protein (GAP-43) in motoneurons. Here, we review our studies on the effects of a 21-aminosteroid on GFAP, NOS, and GAP-43. 4. First, we showed that 21-aminosteroid treatment further increased GFAP-expressing astrocytes in gray matter of the Wobbler spinal cord. This effect may provide neuroprotection if one considers a trophic and beneficial function of astrocytes during the course of degeneration. Other neuroprotectans used in Wobbler mice (T-588) also increased pre-existing astrocytosis. 5. Second, histochemical determination of NADPH-diaphorase, a parameter indicative of neuronal NOS activity, showed that the 21-aminosteroid down-regulated the high activity of this enzyme in ventral horn motoneurons. Therefore, suppression of nitric oxide by decreasing NADPH-diaphorase (NOS) activity may provide neuroprotection considering that excess NO is highly toxic to motoneurons. 6. Finally, 21-aminosteroid treatment significantly attenuated the aberrant expression of both GAP-43 protein and mRNA in Wobbler motoneurons. Hyperexpression of GAP-43 possibly indicated abnormal synaptogenesis, denervation, and muscle atrophy, parameters which may return to normal following antioxidant steroid treatment. 7. Besides 21-aminosteroids, other steroids also behave as neuroprotectans. In this regard, degenerative diseases may constitute potential targets of these hormones, based on the fact that the spinal cord expresses in a regional and cell-specific fashion, receptors for androgens. progesterone, adrenal steroids, and estrogens.

Elevated expression of membrane type 1 metalloproteinase (MT1-MMP) in reactive astrocytes following neurodegeneration in mouse central nervous system

Reactive astrocytes occurring in response to neurodegeneration are thought to play an important role in neuronal regeneration by upregulating the expression of extracellular matrix (ECM) components as well as the ECM degrading metalloproteinases (MMPs). We examined the mRNA levels and cellular distribution of membrane type matrix metalloproteinase 1 (MT1-MMP) and tissue inhibitors 1-4 of MMPs (TIMPs) in brain stem and spinal cord of wobbler (WR) mutant mice affected by progressive neurodegeneration and astrogliosis. MT1-MMP, TIMP-1 and TIMP-3 mRNA levels were elevated, whereas TIMP-2 and TIMP-4 expression was not affected. MT1-MMP was expressed in reactive astrocytes of WR. In primary astrocyte cultures, MT1-MMP mRNA was upregulated by exogeneous tumor necrosis factor alpha. Increased plasma membrane and secreted MMP activities were found in primary WR astrocytes.

Multiplex semi-quantitative reverse transcriptase-polymerase chain reaction of low abundance neuronal mRNAs

The sequential use of reverse transcriptase and the polymerase chain reaction (RT-PCR) has provided molecular biology research with an exquisitely sensitive and fast technique for studying gene expression. This method is particularly useful to study transcripts in the nervous system, which are on average present at low levels and the amount of tissue or cells to be analyzed is often limited. Here, we describe a RT-PCR assay which allows the simultaneous detection and semi-quantitation of several transcripts (multiplex). Multiple PCR primer pairs are used to detect different target transcripts in a single reaction, together with a pair of primers able to amplify the hypoxantine-phosphoribosyl-transferase (HPRT), a gene constitutively expressed at low levels throughout the nervous system. HPRT levels remain constant also during neurogenesis and it is thus apt to be used in developmental neurobiology. This internal standard is the mRNA of reference to evaluate sample variation in RT and PCR reactions and to monitor the degradation and recovery of RNAs. Normalization with respect to HPRT cDNA allows to estimate the relative abundance of each target mRNA.

Experimental models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by the progressive loss of motor neurons, leading to profound weakness and eventual death of affected individuals. For the vast majority of patients with ALS, the etiology of the disorder is unknown, and although multiple clinical trials of various therapeutic agents have been undertaken, truly effective therapy is not currently available for the disease. The selection of treatments used in ALS clinical trials frequently has its basis in promising data obtained from experimental model systems in which the proposed agent has shown some effect in protecting motor neurons from a particular insult. The likelihood of a successful clinical outcome for a given treatment in ALS would therefore depend on two principal factors, including the similarity of the model to the disease and the biologic action of the potential therapeutic agent. Partly because early experimental models of ALS failed to replicate the disease process, treatment success in these models did not carry over into human trials. Recently, however, a variety of newer model systems have been developed and utilized to investigate motor neuron degeneration as related to ALS. For example, in this issue, Corse et al. use a rat spinal cord organotypic slice subjected to glutamate excitotoxicity as a model system to test the effectiveness of neurotrophic factors in preventing motor neuron degeneration. This review will assess the strengths and weaknesses of differing ALS model systems that have been used to preclinically test potential drug efficacy in ALS.

A novel behavioral method to detect motoneuron disease in Wobbler mice aged three to seven days old

The Wobbler mouse possesses an inherited autosomal recessive form of motoneuron disease. The most characteristic abnormality is the degeneration of motoneurons, mostly in the cervical spinal cord, and in the brain stem cranial motor nuclei. The underlying pathology shows up as symptoms that are only detectable confidently around the time of weaning (age 3 weeks). We now report a new method designed to identify presymptomatic Wobbler mice by behavioral and statistical approaches. We measured body weight, righting reflex (RR) and gender to examine whether these parameters have an impact on the status of the disease before age 3 weeks. Using a total of 341 NFR/wr strain pups, we found a strong association between RR and the Wobbler disease status (p<0.0001) between postnatal days 3 to 7, and achieved greater than 97% correct classification of Wobblers. Therefore the measurement of RR allows the early detection of the affected Wobbler (wr/wr) mice with a minimum of error. This method has been used in our laboratory for immunocytochemical studies that show the early sprouting of immunoreactive serotonin and peptidergic fibers in the cervical spinal ventral horn by postnatal days 7 and 12 respectively. The early detection of Wobbler mice thus facilitates significant new understanding regarding the pathogenesis of motoneuron disease. We can now examine potentially therapeutic approaches which may be more effective than when administered in the symptomatic weanlings (work in progress).

Regulation of growth factor gene expression in degenerating motoneurons of the murine mutant wobbler: a cellular patch-sampling/RT-PCR study

Motoneuronal degenerative diseases are characterized by their progressivity; once affected, the motoneurons remain in altered states during an intermediate phase of degeneration prior to their final disappearance. Whether this survival period coincides with active metabolic rearrangements in the affected neuron remains unknown. As a first step toward the elucidation of this question, we developed cDNA pooled samples obtained from degenerating and control motoneuron mRNA populations through cellular patch sampling and RT-PCR, using the murine wobbler mutant as a model of spinal atrophy. Hybridization of the cDNA pools to various markers of intact or degenerating motoneurons allowed us to verify the cellular specificity of the patch sampling and indicated conservation of the original mRNA population complexity. Exploration of transcriptional alterations of genes encoding growth factors thought to be involved in motoneuronal development revealed that gene expression of the neurotrophin BDNF was induced in affected motoneurons, while expression of neurotrophin-3 was present in both neuronal types. Likewise, expression of a member of the epidermal growth factor (EGF) family, the neuregulin transcript sensory motor neuron-derived factor, was detected in both control and degenerating motoneurons, while transforming growth factor alpha, the functional homolog of EGF, was present only in the affected motoneurons. Immunohistochemical detection of corresponding proteins corroborated these observations. These results demonstrate that, during the course of their degeneration, motoneurons can initiate expression of novel genes which lead to the production of molecules endowed with trophic and/or differentiative properties for the neurons themselves and their glial environment. They also validate the use of the developed cDNA pooled samples for further exploration of transcriptional alterations taking place in degenerating motoneurons.

Quantitative reverse transcriptase PCR to gauge increased protease-activated receptor 1 (PAR-1) mRNA copy numbers in the Wobbler mutant mouse

Thrombin acts on cells through the surface protease-activated receptor 1 (PAR-1), a G-protein-coupled member of the seven-transmembrane domain superfamily. On neural cells, thrombin has deleterious effects, killing neurons through apoptosis. Consequently, knowledge of PAR-1 expression in the nervous system may help to elucidate the role of thrombin in neurodegenerative disease. We developed a mimic construct to facilitate the highly sensitive technique of quantitative reverse transcriptase to PCR (qRT-PCR) to measure the differential expression of low copy number PAR-1 mRNA in neurodegenerative model systems. In this article, we report our results comparing homozygous wobbler (wr/wr) mice and normal littermates. By optimizing the transcription and quantitative PCR procedures to facilitate rapid copy number determination in small RNA samples, we documented a fivefold greater level of PAR-1 mRNA in the cervical spinal cord of wr/wr.

The protein kinase N (PKN) gene PRKCL1/Prkcl1 maps to human chromosome 19p12-p13.1 and mouse chromosome 8 with close linkage to the myodystrophy (myd) mutation

Protein kinase N (PKN) is a fatty acid- and Rho-activated serine/threonine protein kinase involved in the regulation of cell motility by association with cytoskeletal components such as neurofilament and alpha-actinin. We determined the chromosomal location of the human PKN gene PRKCL1 by fluorescence in situ hybridization and by radiation hybrid mapping. The corresponding mouse gene Prkcl1 was mapped by segregation analysis. We found by FISH that PRKCL1 is localized to chromosome 19p12-p13.1 and, more precisely, by radiation hybrid mapping, about 11 cR from EST WI-6344 in subband 19p12. Prkcl1 maps to mouse chromosome 8 between D8Mit6 and junb. This region of mouse Chr 8 shows a scrambled syntenic conservation to human chromosomes 4q, 8p, and 19p. As the mouse mutation myodystrophy myd has been mapped to the same region, Prkcl1 is a candidate gene for myd.

Histone gene expression and chromatin structure during spermatogenesis

The chromatin of male germ cells is restructured throughout spermatogenesis. Analysis of differential histone protein patterns at specific stages of spermatogenesis may contribute towards an understanding of the changes in chromatin structure and function during this differentiation process. The most striking changes in histone patterns occur at the stage of pachytene spermatocytes when most of the linker H1 histones are replaced by the testis specific subtype H1t. In addition, replacement of core histone subtypes is observed at this stage. These structural changes precede the reorganization of chromatin at haploid stages when histones are replaced first by transition proteins and then by protamines.

Genetic transfer of the wobbler gene to a C57BL/6J x NZB hybrid stock: natural history of the motor neuron disease and response to CNTF and BDNF cotreatment

Preclinical diagnosis of motor neuron disease (MND) in the wobbler mouse (wr/wr) has been impossible until recently. However, with the development of a new hybrid, the C57BL/6J x New Zealand Black (B6NZB) wr/wr mouse, the polymerase chain reaction (PCR) can be used to establish the preclinical diagnosis. We compared the clinical and histological features of MND and the effects of neurotrophic factor cotreatment between the hybrid B6NZB-wr/wr and the congenic C57BL/6J-wr/wr mice. Clinical assessments of body weight, grip strength, running speed, paw position, and walking pattern were made weekly from age 2 weeks through 8 weeks (n = 10, B6NZB-wr/wr; n = 15, C57BL/6J-wr/wr). Survival was analyzed (n = 7, each strain) as was C5 and C6 spinal cord motoneuron morphology and ventral root histometry (n = 7, each strain). For cotreatment, 8 B6NZB-wr/wr and 7 C57BL/6J-wr/wr mice received subcutaneous ciliary neurotrophic factor (1 mg/kg) and brain-derived neurotrophic factor (5 mg/kg) on alternate days, 6 days/week for 4 weeks. B6NZB-wr/wr mice could be distinguished from C57BL/6J-wr/wr mice at age 3 weeks by a more abnormal paw position (P < 0.01) and walking pattern (P < 0.05) and lower grip strength (P < 0.001) and running speed (P < 0.001). After 3 weeks, the changes continued to be greater in B6NZB-wr/wr mice. Although B6NZB-wr/wr mice were more severely affected early in the disease, their survival was comparable to C57BL/6J-wr/wr mice. Anterior horn cell vacuolar degeneration and myelinated fiber histometry were similar in both strains. The clinical response to CNTF/BDNF cotreatment was marked in both groups although it was weaker in B6NZB-wr/wr mice. Thus, the hybrid B6NZB-wr/wr mice have a more severe clinical phenotype and offer a unique opportunity to study the mechanisms of presymptomatic motor neuron degeneration and the effects of therapeutic agents for human MND.

Strychnine-sensitive and strychnine-insensitive glycine binding sites in the spinal cord of the wobbler mouse

Using quantitative autoradiography, the strychnine-sensitive glycine site and strychnine-insensitive glycine site of the N-methyl-D-aspartate receptor were analyzed in the cervical segment of the spinal cord of the wobbler mouse, which is a purported model of human motor neuron diseases. Significantly increased density of the strychnine-sensitive site was found in the lamina II-inner (+17%) and laminae III & IV (+17%) of wobbler mice. The strychnine-insensitive site was also increased in lamina I & II-outer (+15%), lamina II-inner (+15%), laminae III & IV (+48%), laminae V-VIII (+43%) and lamina X (+26%) of wobbler mice. However, no significant differences were observed for the both sites in the ventral horn where motor neurons are located. These findings suggest that both inhibitory and excitatory-associated glycinergic dysfunctions are involved in the wobbler mouse motor neuron disease.

The human gene ZFP161 on 18p11.21-pter encodes a putative c-myc repressor and is homologous to murine Zfp161 (Chr 17) and Zfp161-rs1 (X Chr)

A clone from a lambda gt11 cDNA expression library of HeLa cells was isolated, sequenced, and shown to encode a new human zinc finger protein. The cDNA of the gene termed ZFP161 has an open reading frame of 1347 bp. The predicted protein comprises 449 amino acid residues and contains five zinc finger motifs of the Krüppel type near the C-terminus and a BTB/POZ domain in the N-terminal region. The protein is 98% homologous to a murine zinc finger protein, ZF5 (M. Numoto et al., 1993, Nucleic Acids Res. 21: 3767-3775), which is a putative transcriptional repressor of c-myc and exhibits growth-suppressive activity in mouse cell lines. Through the use of a panel of somatic cell hybrids for chromosomal assignment and DNAs of somatic cell hybrids containing a deleted chromosome 18 for fine mapping, the human gene ZFP161 was localized to 18p11.21-pter. Therefore, ZFP161 is a candidate gene by position for the holoprosencephaly type 4 gene, HPE4, which is involved in congenital malformations. With DNAs from an interspecific backcross, two homologous mouse genes, Zfp161 and Zfp161-rs1, were mapped to chromosome 17 and the X chromosome, respectively. Mapping of Zfp161 confirms and extends a region of homology between distal mouse chromosome 17 and human 18p.

Spinal muscular atrophy gene wobbler of the mouse: evidence from chimeric spinal cord and testis for cell-autonomous function

Human hereditary neurodegenerative diseases are genetically and mechanistically very heterogeneous and so are spinal muscular atrophies and cerebellar ataxias in the mouse, despite the common phenomenon of neuronal death. In this species, a number of mutations impair spermiogenesis in addition to neuron survival. Among these, the wobbler mutation on proximal chromosome 11 of the mouse leads to motoneuron degeneration in brain stem and spinal cord and to a defect of spermiogenesis. Chimeric mice of the type wr?/wr? <--> +/+ were produced, and their allelic status at the wr locus was determined by PCR diagnosis of a closely linked marker. Two overt chimeras, one female (XX <--> XX) and one male (XY <--> XY) were identified as wr/wr <--> +/+ and analyzed with respect to their pathological phenotype. Although there was patchy astrogliosis in the spinal cords of both chimeras, their motor performances were overtly normal and muscles were without signs of denervation. The male's testes revealed a mosaic pattern of normal and pathological spermatids. As no progeny was derived from wr spermatids, the spermatocytes appear as a primary target of the wr mutation in testis. Our results argue against a humoral mechanism of the wobbler disease and indicate a cell-autonomous action of the wr gene both in testis and in spinal cord.

Dynamin genes Dnm1 and Dnm2 are located on proximal mouse chromosomes 2 and 9, respectively

Dynamins, microtubule-binding GTPases, are encoded by at least three genes in mammals. Two distinct gene-specific cDNAs were used to analyze the segregation of dynamin genes Dnm1 and Dnm2 in a mouse interspecies backcross. The nervous system-expressed gene Dnm1 was localized to Chr 2 between the genes for vimentin and nebulin, within a chromosomal region of conserved synteny to human chromosome 9q, consistent with the localization of the human dynamin-1 gene by FISH (see accompanying paper by Newman-Smith et al., 1997, Genomics 41:286-289). The ubiquitously expressed Dnm2 gene was found to be closely linked to the intercellular adhesion molecule-1 gene, Icam1, in a region with homologies to human chromosomes 19p, 8q, and 11q. Potential relations of both loci to disease genes are discussed.

Expression of nerve-regulated genes in muscles of mouse mutants affected by spinal muscular atrophies and muscular dystrophies

The expression of the genes for the alpha-subunit of AChR (AChR alpha), for the myogenic factors myogenin and MyoD, for the calcium-binding protein parvalbumin (PV), and for the muscular chloride channel CIC-1 was studied in the three mouse spinal muscular atrophies (SMAs). These were the mutants "wobbler" (WR), "muscle deficient" (MDF) and "progressive motor neuronopathy" (PMN). Murine myopathies "muscular dystrophy with myositis" (MDM) and "X-linked muscular dystrophy" (MDX) were used as controls. AChR alpha and myogenin mRNA levels were strongly elevated in muscles affected by SMAs (reflecting denervation), whereas only myogenin mRNA was moderately elevated in MDX and MDM muscles, probably due to fiber regeneration. As in denervated muscle, CIC-1 and PV mRNA levels were lowered in SMAs. No changes were seen in muscles of up to 222-day-old symptomless ciliary neurotrophic factor (CNTF) knockout mice. The patterns of gene expression were characteristic for the type of muscle disease, indicating their possible usefulness for clinical diagnosis.

Reduction of lower motor neuron degeneration in wobbler mice by N-acetyl-L-cysteine

The murine mutant wobbler is a model of lower motoneuron degeneration with associated skeletal muscle atrophy. This mutation most closely resembles Werdnig-Hofmann disease in humans and shares some of the clinical features of amyotrophic lateral sclerosis (ALS). It has been suggested that reactive oxygen species (ROS) may play a role in the pathogenesis of disorders such as ALS. To examine the relationship between ROS and neural degeneration, we have studied the effects of agents such as N-acetyl-L-cysteine (NAC), which reduce free radical damage. Litters of wobbler mice were given a 1% solution of the glutathione precursor NAC in their drinking water for a period of 9 weeks. Functional and neuroanatomical examination of these animals revealed that wobbler mice treated with NAC exhibited (1) a significant reduction in motor neuron loss and elevated glutathione peroxidase levels within the cervical spinal cord, (2) increased axon caliber in the medial facial nerve, (3) increased muscle mass and muscle fiber area in the triceps and flexor carpi ulnaris muscles, and (4) increased functional efficiency of the forelimbs, as compared with untreated wobbler littermates. These data suggest that reactive oxygen species may be involved in the degeneration of motor neurons in wobbler mice and demonstrate that oral administration of NAC effectively reduces the degree of motor degeneration in wobbler mice. This treatment thus may be applicable in the treatment of other lower motor neuropathies.