Overexpression of the cytotoxic T cell (CT) carbohydrate inhibits muscular dystrophy in the dyW mouse model of congenital muscular dystrophy 1A

A number of recent studies have demonstrated therapeutic effects of transgenes on the development of muscle pathology in the mdx mouse model for Duchenne muscular dystrophy, but none have been shown also to be effective in mouse models for laminin alpha2-deficient congenital muscular dystrophy (MDC1A). Here, we show that overexpression of the cytotoxic T cell (CT) GalNAc transferase (Galgt2) is effective in inhibiting the development of muscle pathology in the dy(W) mouse model of MDC1A, much as we had previously shown in mdx animals. Embryonic overexpression of Galgt2 in skeletal muscles using transgenic mice or postnatal overexpression using adeno-associated virus both reduced the extent of muscle pathology in dy(W)/dy(W) skeletal muscle. As with mdx mice, embryonic overexpression of the Galgt2 transgene in dy(W)/dy(W) myofibers inhibited muscle growth, whereas postnatal overexpression did not. Both embryonic and postnatal overexpression of Galgt2 in dy(W)/dy(W) muscle increased the expression of agrin, a protein that, in recombinant form, has been shown to ameliorate disease, whereas laminin alpha1, another disease modifier, was not expressed. Galgt2 over-expression also stimulated the glycosylation of a gly-colipid with the CT carbohydrate, and glycolipids accounted for most of the CT-reactive material in postnatal overexpression experiments. These experiments demonstrate that Galgt2 overexpression is effective in altering disease progression in skeletal muscles of dy(W) mice and should be considered as a therapeutic target in MDC1A.     

Elimination of myostatin does not combat muscular dystrophy in dy mice but increases postnatal lethality

Myostatin is a TGF-beta family member and a negative regulator of skeletal muscle growth. It has been proposed that reduction or elimination of myostatin could be a treatment for degenerative muscle diseases such as muscular dystrophy. Laminin-deficient congenital muscular dystrophy is one of the most severe forms of muscular dystrophy. To test the possibility of ameliorating the dystrophic phenotype in laminin deficiency by eliminating myostatin, we crossed dy(W) laminin alpha2-deficient and myostatin null mice. The resulting double-deficient dy(W)/dy(W);Mstn(-/-) mice had a severe clinical phenotype similar to that of dy(W)/dy(W) mice, even though muscle regeneration was increased. Degeneration and inflammation of muscle were not alleviated. The pre-weaning mortality of dy(W)/dy(W);Mstn(-/-) mice was increased compared to dy(W)/dy(W), most likely due to significantly less brown and white fat in the absence of myostatin, and postweaning mortality was not significantly improved. These results show that eliminating myostatin in laminin-deficiency promotes muscle formation, but at the expense of fat formation, and does not reduce muscle pathology. Any future therapy based on myostatin may have undesirable side effects.     

A targeted Coch missense mutation: a knock-in mouse model for DFNA9 late-onset hearing loss and vestibular dysfunction

Mutations in COCH (coagulation factor C homology) are etiologic for the late-onset, progressive, sensorineural hearing loss and vestibular dysfunction known as DFNA9. We introduced the G88E mutation by gene targeting into the mouse and have created a Coch(G88E/G88E) mouse model for the study of DFNA9 pathogenesis and cochlin function. Vestibular-evoked potential (VsEP) thresholds of Coch(G88E/G88E) mice were elevated at all ages tested compared with wild-type littermates. At the oldest ages, two out of eight Coch(G88E/G88E) mice had no measurable VsEP. Auditory brainstem response (ABR) thresholds of Coch(G88E/G88E) mice were substantially elevated at 21 months but not at younger ages tested. At 21 months, four of eight Coch(G88E/G88E) mice had absent ABRs at all frequencies tested and two of three Coch(G88E)(/+) mice had absent ABRs at three of four frequencies tested. Distortion product otoacoustic emission amplitudes of Coch(G88E/G88E) mice were substantially lower than Coch(+/+) mice and absent in the same Coch(G88E/G88E) mice with absent ABRs. These results suggest that vestibular function is affected beginning as early as 11 months when cochlear function appears to be normal, and dysfunction increases with age. Hearing loss declines substantially at 21 months of age and progresses to profound hearing loss at some to all frequencies tested. This is the only mouse model developed to date where hearing loss begins at such an advanced age, providing an opportunity to study both progressive age-related hearing loss and possible interventional therapies.     

Cell degeneration is not a primary causer for Connexin26 (GJB2) deficiency associated hearing loss

Connexin26 (Cx26, GJB2) mutations can induce congenital deafness and are responsible for ∼50% of nonsyndromic hearing loss in children. Mouse models show that Cx26 deficiency induces cochlear development disorder, hair cell loss, and spiral ganglion (SG) neuron degeneration. Hair cell loss and cell degeneration have been considered as a primary causer responsible for Cx26 deficiency associated hearing loss. In this study, by coincidental examination of cochlear postnatal development with recording of auditory brainstem response (ABR) and hair cell function, we found that occurrence of hearing loss in Cx26 knockout (KO) mice was ahead of hair cell loss and cochlear cell degeneration. ABR was absent at the whole-frequency range (8–40 kHz) after birth. However, cochlear cells including SG neurons had no significant degeneration throughout postnatal development. Severe cochlear hair cell loss and SG neuron degeneration were only visible in middle and basal turns, i.e., in middle and high frequency regions, in the adult Cx26 KO mouse cochlea. Functional tests show that hair cells in Cx26 KO mice functioned normally; outer hair cells retained electromotility. These data suggest that cell degeneration is not a primary causer of Cx26 deficiency associated hearing loss. Some mechanisms other than cell degeneration, such as cochlear development disorders, may play an essential role in this common hereditary deafness.     

Laminin {alpha}1 chain corrects male infertility caused by absence of laminin {alpha}2 chain

Laminins are important for basement membrane structure and function. The laminin alpha2 chain is a major component of muscle basement membranes, and mutations in the laminin alpha2 gene lead to congenital muscular dystrophy in humans and mice. Although the laminin alpha2 chain is prominently expressed in testicular basement membranes, its role in testis has remained unclear. Here, we show that laminin alpha1, alpha2, beta1, beta2, gamma 1, and gamma 3 chains are the major laminin chains in basement membranes of seminiferous tubules. In laminin alpha2 chain-deficient dy(3 K)/dy(3 ASK) mice, lack of laminin alpha2 chain led to concurrent reduction of laminin gamma 3 chain and abnormal testicular basement membranes. Seminiferous tubules of laminin alpha2 chain-deficient dy(3 K)/dy(3 K) mice displayed a defect in the timing of lumen formation, resulting in production of fewer spermatides. We also demonstrate that overexpression of laminin alpha1 chain in testis of dy(3 K)/dy(3 K) mice compensated for laminin alpha2 chain deficiency and significantly reversed the appearance of the histopathological features. We thus provide genetic data that laminin alpha chains are essential for normal testicular function in vivo.     

Laminin-111 protein therapy reduces muscle pathology and improves viability of a mouse model of merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is a lethal muscle-wasting disease that is caused by mutations in the LAMA2 gene, resulting in the loss of laminin-α2 protein. MDC1A patients exhibit severe muscle weakness from birth, are confined to a wheelchair, require ventilator assistance, and have reduced life expectancy. There are currently no effective treatments or cures for MDC1A. Laminin-α2 is required for the formation of heterotrimeric laminin-211 (ie, α2, β1, and γ1) and laminin-221 (ie, α2, β2, and γ1), which are major constituents of skeletal muscle basal lamina. Laminin-111 (ie, α1, β1, and γ1) is the predominant laminin isoform in embryonic skeletal muscle and supports normal skeletal muscle development in laminin-α2-deficient muscle but is absent from adult skeletal muscle. In this study, we determined whether treatment with Engelbreth-Holm-Swarm-derived mouse laminin-111 protein could rescue MDC1A in the dy(W-/-) mouse model. We demonstrate that laminin-111 protein systemically delivered to the muscles of laminin-α2-deficient mice prevents muscle pathology, improves muscle strength, and dramatically increases life expectancy. Laminin-111 also prevented apoptosis in laminin-α2-deficient mouse muscle and primary human MDC1A myogenic cells, which indicates a conserved mechanism of action and cross-reactivity between species. Our results demonstrate that laminin-111 can serve as an effective protein substitution therapy for the treatment of muscular dystrophy in the dy(W-/-) mouse model and establish the potential for its use in the treatment of MDC1A.     

Proteasome inhibition improves the muscle of laminin α2 chain-deficient mice

Muscle atrophy, a significant characteristic of congenital muscular dystrophy with laminin α2 chain deficiency (also known as MDC1A), occurs by a change in the normal balance between protein synthesis and protein degradation. The ubiquitin-proteasome system (UPS) plays a key role in protein degradation in skeletal muscle cells. In order to identify new targets for drug therapy against MDC1A, we have investigated whether increased proteasomal degradation is a feature of MDC1A. Using the generated dy(3K)/dy(3K) mutant mouse model of MDC1A, we studied the expression of members of the ubiquitin-proteasome pathway in laminin α2 chain-deficient muscle, and we treated dy(3K)/dy(3K) mice with the proteasome inhibitor MG-132. We show that members of the UPS are upregulated and that the global ubiquitination of proteins is raised in dystrophic limb muscles. Also, phosphorylation of Akt is diminished in diseased muscles. Importantly, proteasome inhibition significantly improves the dystrophic dy(3K)/dy(3K) phenotype. Specifically, treatment with MG-132 increases lifespan, enhances locomotive activity, enlarges muscle fiber diameter, reduces fibrosis, restores Akt phosphorylation and decreases apoptosis. These studies promote better understanding of the disease process in mice and could lead to a drug therapy for MDC1A patients.     

Merosin (laminin-2) localization in basal lamina of normal skeletal muscle fibers and changes in plasma membrane of merosin-deficient skeletal muscle fibers

Primary deficiency of merosin causes a severe congenital muscular dystrophy (CMD) and a mouse dystrophy (dy/dy mouse). Also, its secondary deficiency is seen in some CMD with abnormal glycosylation of -dystroglycan, an extracellular membrane protein, which is the receptor of merosin and binds to dystrophin underlying the sarcolenma via -dystroglycan, a transmembrane protein. In immunogold and freeze-etch electron microscopic studies, merosin in basal lamina of normal skeletal muscles has a zonation in the distribution and is localized at the lamina lucida of muscle basal lamina, and dystrophin molecules are often closed to merosin molecules at the inside and outside surface of muscle plasma membrane. Moreover, merosin molecules exist as the short fine cross-bridge fibrils connecting the basal lamina to the neighboring outer leaflet of the muscle plasma membrane. In freeze-fracture studies, the changes in muscle plasma membranes of dy/dy mice reveal a markedly decreased density of orthogonal arrays (OAs) but normal density of intramembranous particles (IMPs), whereas depletions of IMPs with decreased OAs have been found in Fukyama-type congenital muscular dystrophy, Duchenne muscular dystrophy, and mdx mice. Thus, further studies including the functional role of OAs would be required to understand the pathomechanism of merosin-deficient CMD.     

Age-dependent effect of myostatin blockade on disease severity in a murine model of limb-girdle muscular dystrophy

Myostatin (MSTN) is a muscle-specific secreted peptide that functions to limit muscle growth through an autocrine regulatory feedback loop. Loss of MSTN activity in cattle, mice, and humans leads to a profound phenotype of muscle overgrowth, associated with more and larger fibers and enhanced regenerative capacity. Deletion of MSTN in the mdx mouse model of Duchenne muscular dystrophy enhances muscle mass and reduces disease severity. In contrast, loss of MSTN activity in the dyW/dyW mouse model of laminin-deficient congenital muscular dystrophy, a much more severe and lethal disease model, does not improve all aspects of muscle pathology. Here we examined disease severity associated with myostatin (mstn-/-) deletion in mice nullizygous for delta-sarcoglycan (scgd-/-), a model of limb-girdle muscular dystrophy. Early loss of MSTN activity achieved either by monoclonal antibody administration or by gene deletion each improved muscle mass, regeneration, and reduced fibrosis in scgd-/- mice. However, antibody-mediated inhibition of MSTN in late-stage dystrophic scgd-/- mice did not improve disease. These findings suggest that MSTN inhibition may benefit muscular dystrophy when instituted early or if disease is relatively mild but that MSTN inhibition in severely affected or late-stage disease may be ineffective.     

卡那霉素对小鼠耳蜗内毛细胞带状突触数量的影响

目的通过研究卡那霉素对小鼠耳蜗内毛细胞带状突触数量的影响,探讨卡那霉素耳毒性的发病机制。方法实验组昆明小鼠分为6组,每组10只,每日丁胺卡那霉素(400mg/kg)进行肌肉注射,并于第0d、第3d、第7d、第10d、第14d、和第21d取耳蜗基底膜顶回作为标本。对照组(每组10只)采用等体积生理盐水肌肉注射。使用免疫荧光双标法对耳蜗内毛细胞带状突触前膜RIBEYE蛋白和突触后膜GluR2&3蛋白进行标记,激光共聚焦显微镜对耳蜗基底膜顶回进行光学连续切片,运用3dMax8.0软件对带状突触进行三维建模及重构,并观察带状突触形态变化和计算其数量改变。结果所有小鼠耳蜗内毛细胞轮廓完整,但内毛细胞带状突触数量存在差异。与生理盐水对照组相比,在卡那霉素注射初期带状突触数量未见明显变化,给药第7d时内毛细胞带状突触数量显著增加,第21d显著下降。结论卡那霉素连续作用21d,耳蜗内毛细胞带状突触数量呈先增高后降低的趋势。     

Interaction of merosin (laminin 2) with very late activation antigen-6 is necessary for the survival of CD4+ CD8+ immature thymocytes

The laminin alpha2-chain is a component of merosin, a member of the laminin family molecules, which is mainly expressed in the basement membranes of striated muscle. It is known that laminin alpha2 gene (lama2) null mutant mice (dy3k/dy3k) exhibit congenital muscular dystrophy (CMD). Because the laminin alpha2-chain is also expressed in the thymus, the role of merosin in the thymus was examined. In association with the onset of muscular dystrophy, CD4+ CD8+ double-positive (DP) thymocytes disappear by apoptotic cell death, while CD4+ CD8- or CD4- CD8+ thymocytes remain. In order to study the mechanisms leading to the selective death of DP cells in the absence of merosin, the role of the interaction between very late activation antigen-6 (VLA-6), a candidate merosin ligand in the thymus, and merosin was examined. The in vitro survival of thymocytes from normal mice was maintained by the addition of either anti-VLA-6 monoclonal antibodies (mAbs) or merosin. Furthermore, when the normal thymocytes were cultured on thymic epithelial cell lines, viable DP cell recoveries on wild-type epithelial cells were better than on cells from null mutant mice. The results suggest that DP cells are more sensitive to an uncharacterized apoptotic death signal, and that survival is supported by the interaction between VLA-6 and merosin.     

Esketamine may be an ideal substitute for ketamine during cochlear function measurement

The mixture of ketamine and xylazine is widely used for the auditory brainstem response (ABR) measurement. Esketamine is twice as potent as ketamine. Our objective was to assess the influence of esketamine in mice undergoing cochlear function measurement including ABR and distortion product otoacoustic emission (DPOAE) measurement. C57Bl/6J mice were treated with an equivalent dose of analgesia and received either a single intraperitoneal (ip) injection of 100 mg/kg ketamine and 25 mg/kg xylazine or 50 mg/kg esketamine and 25 mg/kg xylazine. Hearing thresholds, peak latencies of waves I and V, and DPOAE thresholds were recorded. Time to loss of righting and time to regain righting were also assessed. We found that hearing thresholds, the peak latencies of waves I and V, and DPOAE thresholds were similar between the two groups (all P>0.05). Time to regain righting was significantly shorter in the esketamine group (P<0.001) than in the ketamine group. We concluded that when using equivalent doses of analgesia, esketamine may be an ideal substitute for ketamine during cochlear function test.     

Skeletal,cardiac and tongue muscle pathology,defective retinal transmission,and neuronal migration defects in the Large(myd) mouse defines a natural model for glycosylation-deficient muscle - eye - brain disorders

We have recently shown that a deletion in the Large gene, encoding a putative glycosyltransferase, is the molecular defect underlying the myodystrophy (previously myd; now Large(myd)) mouse. Here we show that the muscular dystrophy phenotype is not confined to skeletal muscle, but is also present in the heart and tongue. Immunohistochemistry indicates disruption of the dystrophin-associated glycoprotein complex (DGC) in skeletal and cardiac muscle. Quantitative western blotting shows a general increase in the expression of DGC proteins and of dysferlin and caveolin-3 in mutant skeletal muscle. In contrast, the expression of DGC proteins is reduced in cardiac muscle. Overlay assays show loss of laminin binding by alpha-dystroglycan in Large(myd) skeletal and cardiac muscle and in brain. We also show that the phenotype of Large(myd) mice is not restricted to muscular dystrophy, but also includes ophthalmic and central nervous system (CNS) defects. Electroretinograms of homozygous mutant mice show gross abnormalities of b-wave characteristics, indicative of a complex defect in retinal transmission. The laminar architecture of the cortices of the cerebrum and the cerebellum is disturbed, indicating defective neuronal migration. Thus, the phenotype of the Large(myd) mouse shows similarities to the heterogeneous group of human muscle eye brain diseases characterized by severe congenital muscular dystrophy, eye abnormalities and CNS neuronal migration defects. These diseases include Fukuyama-type muscular dystrophy and muscle-eye-brain disease, both of which are also due to mutations in predicted glycosylation enzymes. Therefore, the Large(myd) mouse represents an important animal model for studying the function of glycosylation in muscle, brain and retina.     

Detection and differentiation of sensorineural hearing loss in mice using auditory steady-state responses and transient auditory brainstem responses

Sensorineural hearing loss (SNHL) comprises hearing disorders with diverse pathologies of the inner ear and the auditory nerve. To date, an unambiguous phenotypical characterization of the specific pathologies in an affected individual remains impossible. Here, we evaluated the use of scalp-recorded auditory steady-state responses (ASSR) and transient auditory brainstem responses (ABR) for differentiating the disease mechanisms underlying sensorineural hearing loss in well-characterized mouse models. We first characterized the ASSR evoked by sinusoidally amplitude-modulated tones in wild-type mice. ASSR were robustly elicited within three ranges of modulation frequencies below 200 Hz, from 200 to 600 Hz and beyond 600 Hz in most recordings. Using phase information we estimated the apparent ASSR latency to be about 3 ms, suggesting generation in the auditory brainstem. Auditory thresholds obtained by automated and visual analysis of ASSR recordings were comparable to those found with tone-burst evoked ABR in the same mice. We then recorded ASSR and ABR from mouse mutants bearing defects of either outer hair cell amplification (KCNQ4-knockout) or inner hair cell synaptic transmission (Bassoon-mutant). Both mutants showed an increase of ASSR and ABR thresholds of approximately 40 dB versus wild-type when investigated at 8 weeks of age. Mice with defective amplification displayed a steep rise of ASSR and ABR amplitudes with increasing sound intensity, presumably reflecting a strong recruitment of synchronously activated neural elements beyond threshold. In contrast, the amplitudes of ASSR and ABR responses of mice with impaired synaptic transmission grew very little with sound intensity. In summary, ASSR allow for a rapid, objective and frequency-specific hearing assessment and together with ABR and otoacoustic emissions can contribute to the differential diagnosis of SNHL.     

Fukutin is required for maintenance of muscle integrity,cortical histiogenesis and normal eye development

Fukuyama-type congenital muscular dystrophy (FCMD), one of the most common autosomal-recessive disorders in Japan, is characterized by congenital muscular dystrophy associated with brain malformation due to a defect during neuronal migration. Through positional cloning, we previously identified the gene for FCMD, which encodes the fukutin protein. Here we report that chimeric mice generated using embryonic stem cells targeted for both fukutin alleles develop severe muscular dystrophy, with the selective deficiency of alpha-dystroglycan and its laminin-binding activity. In addition, these mice showed laminar disorganization of the cortical structures in the brain with impaired laminin assembly, focal interhemispheric fusion, and hippocampal and cerebellar dysgenesis. Further, chimeric mice showed anomaly of the lens, loss of laminar structure in the retina, and retinal detachment. These results indicate that fukutin is necessary for the maintenance of muscle integrity, cortical histiogenesis, and normal ocular development and suggest the functional linkage between fukutin and alpha-dystroglycan.     

Inner hair cell ribbon synapse plasticity might be molecular basis of temporary hearing threshold shifts in mice

Recent studies have reported that noise exposure at relatively low intensities can cause temporary threshold shifts (TTS) in hearing. However, the mechanism underlying the TTS is still on debate. Here, we report that an acoustic stimulation (100 dB SPL, white noise) induced TTS in mice, with the maximal ABR threshold elevations seen on the 4^th day after noise exposure. On the other hand, there were no significant morphological changes in the cochlea. Further, there were paralleled changes of pre-synaptic ribbons in both the number and postsynaptic density (PSDs) during this noise exposure. The numbers of presynaptic ribbon, postsynaptic density (PSDs), and colocalized puncta correlated with the shifts of ABR thresholds. Moreover, a complete recovery of ABR thresholds and synaptic puncta was seen on the 14^th day after the noise stimulations. Thus, our study may indicate that noise exposure can cause a decline in cochlear ribbon synapses and result in consequent hearing loss. The reduction of synaptic puncta appears reversible and may contribute to hearing restoration in mice after noise exposure.     

小鼠听觉剥夺动物模型的建立

目的 探索一种建立稳定的小鼠听觉剥夺动物模型的方法.方法 选取出生2个月、听觉脑干诱发电位(ABR)正常的BALB/c小鼠40只,随机分为两组各20只.实验组采用耳后径路开放听泡,用微型钻在耳蜗表面钻孔损毁双侧耳蜗结构;对照组仅做耳后切口不破坏耳蜗结构.术后动物饲养4个月,通过比较手术前后ABR测试结果,进行客观听力学评估.结果 实验组小鼠术后耳廓反射消失,ABR测试未检测出反应波形.对照组听力正常.结论 耳后径路切除小鼠耳蜗,能够建立稳定可靠的听觉剥夺动物模型,对于听觉中枢可塑性的研究很有价值.     

GFAP aggregates in the cochlear nerve increase the noise vulnerability of sensory cells in the organ of Corti in the murine model of Alexander disease

Outer hair cell (OHC) loss in the auditory sensory epithelium is a primary cause of noise-induced sensory-neural hearing loss (SNHL). To clarify the participation of glial cells in SNHL, we used an Alexander disease (AxD) mouse model. These transgenic mice harbor the AxD causal mutant of the human glial fibrillary acidic protein (GFAP) under the control of the mouse GFAP promoter. It is thought that GFAP aggregates compromise the function of astrocytes. In the auditory pathway, the formation of GFAP aggregates was observed only in GFAP-positive cells of the cochlear nerve. The presence of GFAP aggregates did not change auditory function at the threshold level. To assess the change in vulnerability to auditory excitotoxicity, both transgenic and control mice were treated with intense noise exposure. Auditory threshold shifts were assessed by auditory brainstem responses (ABR) at 1 and 4 weeks after noise exposure, and OHC damage was analyzed by quantitative histology at 4 weeks after exposure. Transgenic mice showed more severe ABR deficits and OHC damage, suggesting that cochlear nerve glial cells with GFAP aggregates play a role in noise susceptibility. Thus, we should focus more on the roles of cochlear nerve glial cells in SNHL.     

Activation of the lama2 gene in muscle regeneration: abortive regeneration in laminin alpha2-deficiency

Mutations in laminin alpha2, a subunit of the basement membrane protein laminin-2/merosin, cause merosin-deficient congenital muscular dystrophy. To gain insight into the molecular mechanism of disease, we generated and used a mutant mouse, dyW, in which the lacZ gene was inserted into the lama2 gene so that beta-galactosidase would be expressed in place of laminin alpha2. Heterozygous and homozygous mutant mice are normal at birth, but homozygous mice develop muscular dystrophy at 2 to 3 weeks of age. The lama2/lacZ gene was highly expressed in muscle in the early stages of embryonic myogenesis, but was down-regulated at later stages in both heterozygous and homozygous mice. No beta-galactosidase activity was detected in skeletal muscle after birth in adult heterozygous mice. In contrast, high beta-galactosidase activity was detected in postnatal homozygous mice. Induction of injury in heterozygous mice resulted in intense reexpression of beta-galactosidase in the injured muscle early in regeneration, with a decline in enzyme activity as repair of the tissue progressed. Although the initial response to injury was similar in heterozygous and homozygous mice with abundant beta-galactosidase-positive, mononucleated cells in the injured area, repair was rarely completed in the homozygous mice, evidently caused by excessive death of cells associated with immature myofibers. The defect in muscle repair was very efficiently corrected in homozygous dyW mice expressing a human LAMA2 transgene in skeletal muscle. The data show the importance of laminin alpha2 in muscle regeneration and suggest that a major contributor to disease in muscular dystrophy is abortive regeneration.     

Auditory development in progressive motor neuronopathy mouse mutants

The present study was performed to elucidate the hearing development in the progressive motor neuronopathy (pmn) mouse mutant. This mouse has been used as a model for human motoneuron disease. A missense mutation in the tubulin-specific chaperon E (Tbce) gene on mouse chromosome 13 was localized as the underlying genetic defect. The protein encoded by the Tbce gene is essential for the formation of primary tubulin complexes. Studies on motoneurons show disorganization in microtubules and disturbed axonal transport, followed by retrograde degeneration of the motoneurons. A similar pathomechanism is also possible for hearing disorders where disrupted microtubules could cause functional deficits in spiral ganglion neurons or in cochlear hair cells. Click auditory brainstem response (ABR) audiometry in homozygous pmn mutants showed a normal onset of hearing, but an increasing hearing threshold from postnatal day 26 (P26) on to death, compared to heterozygous mutants and wild-type mice. Histological sections of the cochlea at different ages showed a regular morphology. Additionally, spiral ganglion explants from mutant and wild-type mice were cultured. The neurite length from pmn mutants was shorter than in wild-type mice, and the neurite number/explant was significantly decreased in pmn mutants. We show that the pmn mouse mutant is a model for a progressive rapid hearing loss from P26 on, after initially normal hearing development. Heterozygous mice are not affected by this defect. With the knowledge of the well-known pathomechanism of this defect in motoneurons, a dysfunction of cellular mechanisms regulating tubulin assembling suggests that tubulin assembling plays an essential role in hearing function and maintenance.