VDAC3 has differing mitochondrial functions in two types of striated muscles.

Voltage-dependent anion channel (VDAC) is an abundant mitochondrial outer membrane protein. In mammals, three VDAC isoforms have been characterized. We have previously reported alterations in the function of mitochondria when assessed in situ in different muscle types in VDAC1 deficient mice (Anflous et al., 2001). In the present report we extend the study to VDAC3 deficient muscles and measure the respiratory enzyme activity in both VDAC1 and VDAC3 deficient muscles. While in the heart the absence of VDAC3 causes a decrease in the apparent affinity of in situ mitochondria for ADP, in the gastrocnemius, a mixed glycolytic/oxidative muscle, the affinity of in situ mitochondria for ADP remains unchanged. The absence of VDAC1 causes multiple defects in respiratory complex activities in both types of muscle. However, in VDAC3 deficient mice the defect is restricted to the heart and only to complex IV. These functional alterations correlate with structural aberrations of mitochondria. These results demonstrate that, unlike VDAC1, there is muscle-type specificity for VDAC3 function and therefore in vivo these two isoforms may fulfill different physiologic functions.

Spinocerebellar ataxia with axonal neuropathy: consequence of a Tdp1 recessive neomorphic mutation?

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) cleaves the phosphodiester bond between a covalently stalled topoisomerase I (Topo I) and the 3' end of DNA. Stalling of Topo I at DNA strand breaks is induced by endogenous DNA damage and the Topo I-specific anticancer drug camptothecin (CPT). The H493R mutation of Tdp1 causes the neurodegenerative disorder spinocerebellar ataxia with axonal neuropathy (SCAN1). Contrary to the hypothesis that SCAN1 arises from catalytically inactive Tdp1, Tdp1-/- mice are indistinguishable from wild-type mice, physically, histologically, behaviorally, and electrophysiologically. However, compared to wild-type mice, Tdp1-/- mice are hypersensitive to CPT and bleomycin but not to etoposide. Consistent with earlier in vitro studies, we show that the H493R Tdp1 mutant protein retains residual activity and becomes covalently trapped on the DNA after CPT treatment of SCAN1 cells. This result provides a direct demonstration that Tdp1 repairs Topo I covalent lesions in vivo and suggests that SCAN1 arises from the recessive neomorphic mutation H493R. This is a novel mechanism for disease since neomorphic mutations are generally dominant.

Dual pathology in Rasmussen's encephalitis: a study of seven cases and review of the literature.

Dual pathology has previously been reported in less than 10% of cases of Rasmussen's encephalitis (RE). Given the rarity of RE, it appears unlikely that dual pathology in RE is merely a coincidence. We therefore reviewed all cases of RE experienced in our institution to assess for an additional/associated pathology. A total of seven patients with RE were identified in our archives. Seven children (4 boys and 3 girls, age range: 3-16 years, mean: 9.5 years) with medically refractory epilepsy underwent surgical resection for intractable seizures. The surgical specimens were examined with routine neurohistological techniques, and immunohistochemistry was performed with an extensive panel of antibodies for viruses, lymphocytes, microglia/macrophages, human leukocyte antigen (HLA)-DR, astrocytes, and neurons. Relevant literature was reviewed. Microscopically, all seven cases demonstrated the inflammatory pathology of RE in the cortex and white matter with leptomeningeal and perivascular lymphocytic infiltration, microglial nodules with/without neuronophagia, neuronal loss and gliosis. The HLA-DR antibody was extremely helpful in highlighting the extent of microglial cell proliferation/activation that was not appreciable with standard histology. An unexpected finding in all seven cases was the presence of cortical dysplasia. In our series of seven cases, there was co-occurrence of the inflammatory/destructive pathology of RE with malformative/dysplastic features in cortical architecture in 100% of cases, raising questions about the possible relationships between the two entities. Awareness of the possibility of dual pathology in RE is important for clinical and pathological diagnosis, and may affect the management and outcome of these patients. Immunohistochemistry is very helpful to make a definitive diagnosis of both pathologies.

Dendritic spine pathologies in hippocampal pyramidal neurons from Rett syndrome brain and after expression of Rett-associated MECP2 mutations.

Rett syndrome (RTT) is an X chromosome-linked neurodevelopmental disorder associated with the characteristic neuropathology of dendritic spines common in diseases presenting with mental retardation (MR). Here, we present the first quantitative analyses of dendritic spine density in postmortem brain tissue from female RTT individuals, which revealed that hippocampal CA1 pyramidal neurons have lower spine density than age-matched non-MR female control individuals. The majority of RTT individuals carry mutations in MECP2, the gene coding for a methylated DNA-binding transcriptional regulator. While altered synaptic transmission and plasticity has been demonstrated in Mecp2-deficient mouse models of RTT, observations regarding dendritic spine density and morphology have produced varied results. We investigated the consequences of MeCP2 dysfunction on dendritic spine structure by overexpressing ( approximately twofold) MeCP2-GFP constructs encoding either the wildtype (WT) protein, or missense mutations commonly found in RTT individuals. Pyramidal neurons within hippocampal slice cultures transfected with either WT or mutant MECP2 (either R106W or T158M) showed a significant reduction in total spine density after 48 h of expression. Interestingly, spine density in neurons expressing WT MECP2 for 96 h was comparable to that in control neurons, while neurons expressing mutant MECP2 continued to have lower spine density than controls after 96 h of expression. Knockdown of endogenous Mecp2 with a specific small hairpin interference RNA (shRNA) also reduced dendritic spine density, but only after 96 h of expression. On the other hand, the consequences of manipulating MeCP2 levels for dendritic complexity in CA3 pyramidal neurons were only minor. Together, these results demonstrate reduced dendritic spine density in hippocampal pyramidal neurons from RTT patients, a distinct dendritic phenotype also found in neurons expressing RTT-associated MECP2 mutations or after shRNA-mediated endogenous Mecp2 knockdown, suggesting that this phenotype represent a cell-autonomous consequence of MeCP2 dysfunction.

SCA7 knockin mice model human SCA7 and reveal gradual accumulation of mutant ataxin-7 in neurons and abnormalities in short-term plasticity.

We targeted 266 CAG repeats (a number that causes infantile-onset disease) into the mouse Sca7 locus to generate an authentic model of spinocerebellar ataxia type 7 (SCA7). These mice reproduced features of infantile SCA7 (ataxia, visual impairments, and premature death) and showed impaired short-term synaptic potentiation; downregulation of photoreceptor-specific genes, despite apparently normal CRX activity, led to shortening of photoreceptor outer segments. Wild-type ataxin-7 was barely detectable, as was mutant ataxin-7 in young animals; with increasing age, however, ataxin-7 staining became more pronounced. Neurons that appeared most vulnerable had relatively high levels of mutant ataxin-7; it is interesting, however, that marked dysfunction occurred in these neurons weeks prior to the appearance of nuclear inclusions. These data demonstrate that glutamine expansion stabilizes mutant ataxin-7, provide an explanation for selective neuronal vulnerability, and show that mutant ataxin-7 impairs posttetanic potentiation (PTP).

A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration.

To faithfully recreate the features of the human neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) in the mouse, we targeted 154 CAG repeats into the endogenous mouse locus. Sca1(154Q/2Q) mice developed a progressive neurological disorder that resembles human SCA1, featuring motor incoordination, cognitive deficits, wasting, and premature death, accompanied by Purkinje cell loss and age-related hippocampal synaptic dysfunction. Mutant ataxin-1 solubility varied with brain region, being most soluble in the neurons most vulnerable to degeneration. Solubility decreased overall as the mice aged; Purkinje cells, the most affected in SCA1, did not form aggregates of mutant protein until an advanced stage of disease. It appears that those neurons that cannot sequester the mutant protein efficiently and thereby curb its toxicity suffer the worst damage from polyglutamine-induced toxicity.

Neurologic phenotype of Schimke immuno-osseous dysplasia and neurodevelopmental expression of SMARCAL1.

Schimke immuno-osseous dysplasia (OMIM 242900) is an uncommon autosomal-recessive multisystem disease caused by mutations in SMARCAL1 (swi/snf-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1), a gene encoding a putative chromatin remodeling protein. Neurologic manifestations identified to date relate to enhanced atherosclerosis and cerebrovascular disease. Based on a clinical survey, we determined that half of Schimke immuno-osseous dysplasia patients have a small head circumference, and 15% have social, language, motor, or cognitive abnormalities. Postmortem examination of 2 Schimke immuno-osseous dysplasia patients showed low brain weights and subtle brain histologic abnormalities suggestive of perturbed neuron-glial migration such as heterotopia, irregular cortical thickness, incomplete gyral formation, and poor definition of cortical layers. We found that SMARCAL1 is highly expressed in the developing and adult mouse and human brain, including neural precursors and neuronal lineage cells. These observations suggest that SMARCAL1 deficiency may influence brain development and function in addition to its previously recognized effect on cerebral circulation.

Schimke immuno-osseous dysplasia: a clinicopathological correlation.

BACKGROUND: Schimke immuno-osseous dysplasia (SIOD) is a fatal autosomal recessive disorder caused by loss-of-function mutations in swi/snf-related matrix-associated actin-dependent regulator of chromatin, subfamily a-like 1 (SMARCAL1). METHODS: Analysis of detailed autopsies to correlate clinical and pathological findings in two men severely affected with SIOD. RESULTS: As predicted by the clinical course, T cell deficiency in peripheral lymphoid organs, defective chondrogenesis, focal segmental glomerulosclerosis, cerebral ischaemic lesions and premature atherosclerosis were identified. Clinically unexpected findings included a paucity of B cells in the peripheral lymphoid organs, emperipolesis-like (penetration of one cell by another) abnormalities in the adenohypophysis, fatty infiltration of the cardiac right ventricular wall, pulmonary emphysema, testicular hypoplasia with atrophy and azospermia, and clustering of small cerebral vessels. CONCLUSIONS: A regulatory role for the SMARCAL1 protein in the proliferation of chondrocytes, lymphocytes and spermatozoa, as well as in the development or maintenance of cardiomyocytes and in vascular homoeostasis, is suggested. Additional clinical management guidelines are recommended as this study has shown that patients with SIOD may be at risk of pulmonary hypertension, combined immunodeficiency, subcortical ischaemic dementia and cardiac dysfunction.

Expression analysis of juvenile pilocytic astrocytomas by oligonucleotide microarray reveals two potential subgroups.

Juvenile pilocytic astrocytoma (JPA) is one of the most common brain tumors in children. The expression profiles of 21 JPAs, determined using Affymetrix GeneChip U133A, were compared with subjects with normal cerebella. The genes involved in neurogenesis, cell adhesion, synaptic transmission, central nervous system development, potassium ion transport, protein dephosphorylation, and cell differentiation were found to be significantly deregulated in JPA. These 21 JPAs were further clustered into two major groups by unsupervised hierarchical clustering using a set of 848 genes with high covariance (0.5-10). Supervised analysis with Significance Analysis of Microarrays software between these two potential subgroups identified a list of significant differentially expressed genes involved in cell adhesion, regulation of cell growth, cell motility, nerve ensheathment, and angiogenesis. Immunostaining of myelin basic protein on paraffin sections derived from 18 incompletely resected JPAs suggests that JPA without myelin basic protein-positively stained tumor cells may have a higher tendency to progress.

Reelin and disabled-1 expression in developing and mature human cortical neurons.

In developing mammalian (mouse) brain, Reelin (Reln) is secreted by the Cajal-Retzius (CR) neurons in the marginal zone, binds apolipoprotein E receptor 2 (ApoER2) and very low density lipoprotein receptor (Vldlr), and induces the phosphorylation of the downstream cytoplasmic molecule disabled-1 (Dab1) in cortical plate neurons. Although this is a well-characterized signaling pathway in mice, it has not been well defined in human brain. In this paper we examined the expression of RELN, APOER2, VLDLR, and DAB1 in the developing human brain by RT-PCR. We further determined the cellular expression of the proteins RELN and DAB1 in 50 human brains ranging in age from 10 gestational weeks (GW) to 62 years using immunochemistry. We found that the pattern of expression of RELN and DAB1 in the human brain isnot identical to that observed in the mouse brain. In particular, we report the novel finding that human DAB1and RELN are coexpressed in CR neurons during cortical development and in cortical pyramidal neurons after neuronal migration is complete. Thus, in the human brain, the whole RELN signaling pathway is present within selected populations of cortical neurons throughout life. We speculate that RELN and DAB1 coexpression in these neurons is necessary for both normal cortical development and mature function.

Neonatal presentation of ventricular tachycardia and a Reye-like syndrome episode associated with disturbed mitochondrial energy metabolism.

BACKGROUND: Hyperammonemia, hypoglycemia, hepatopathy, and ventricular tachycardia are common presenting features of carnitine-acylcarnitine translocase deficiency (Mendelian Inheritance in Man database: *212138), a mitochondrial fatty acid oxidation disorder with a lethal prognosis. These features have not been identified as the presenting features of mitochondrial cytopathy in the neonatal period. CASE PRESENTATION: We describe an atypical presentation of mitochondrial cytopathy in a 2 day-old neonate. She presented with a Reye-like syndrome episode, premature ventricular contractions and ventricular tachycardia. Initial laboratory evaluation exhibited a large amount of 3-methylglutaconic acid on urine organic acid analysis, mild orotic aciduria and a nonspecific abnormal acylcarnitine profile. The evaluation for carnitine-acylcarnitine translocase deficiency and other fatty acid oxidation disorders was negative. The patient later developed a hypertrophic cardiomyopathy and continued to be affected by recurrent Reye-like syndrome episodes triggered by infections. A muscle biopsy exhibited signs of a mitochondrial cytopathy. During the course of her disease, her Reye-like syndrome episodes have subsided; however, cardiomyopathy has persisted along with fatigue and exercise intolerance. CONCLUSIONS: This case illustrates that, in the neonatal period, hyperammonemia and ventricular tachycardia may be the presenting features of a lethal carnitine-acylcarnitine translocase deficiency or of a mitochondrial cytopathy, associated with a milder clinical course. This association broadens the spectrum of presenting phenotypes observed in patients with disturbed mitochondrial energy metabolism. Also, the presence of 3-methylglutaconic aciduria suggests mitochondrial dysfunction and mild orotic aciduria could potentially be used as a marker of mitochondrial disease.

Sudden death, febrile seizures, and hippocampal and temporal lobe maldevelopment in toddlers: a new entity.

Recently, we reported hippocampal and temporal lobe abnormalities in 5 toddlers with sudden unexplained death in childhood (SUDC). The association of these anomalies with a high incidence (40%) of individual/family histories of simple febrile seizures in the cases raised concern that febrile seizures can be associated with death. In a series of 64 toddlers with sudden death, we tested the hypothesis that an SUDC subset is characterized by hippocampal and temporal lobe maldevelopment and an individual and/or family history of simple familial seizures. Cases of sudden and unexplained death in children aged 1.0 to 5.9 years (median 1.7 years) were divided into groups based upon a history of febrile or nonfebrile seizures, familial febrile seizures, and autopsy classification of cause of death. Forty-nine of the 64 cases (77%) were classified as SUDC, of which 40% had an individual/family history of febrile seizures. Of the 26 SUDC cases with available hippocampal sections, 62% (16/26) had hippocampal and temporal lobe anomalies, including 82% (9/11) of cases with an individual/family history of febrile seizures. Cases with these anomalies were all found dead during a sleep period, typically in the prone (87%) position. We conclude that a potential new entity may account for the majority of SUDC in toddlers, defined by sleep-related death in the prone position, individual/family history of febrile seizures, and hippocampal and temporal lobe anomalies. The mechanism of death appears analogous to sudden death in (temporal lobe) epilepsy, with a putative unwitnessed seizure during sleep leading to airway occlusion and death. This study mandates further research into the potential link between simple febrile seizures and death.

Evidence of increased cell proliferation in the hippocampus in children with Ammon's horn sclerosis.

Previous studies of Ammon's horn sclerosis (AHS) suggest that AHS is both the result of and the cause of seizures, and support the idea that seizures cause alterations in cell numbers and location. To test the hypothesis that epilepsy induces neurogenesis/gliogenesis, hippocampal cell proliferation was assessed in AHS. Twelve and four resected hippocampi in patients with AHS and with tumor-related epilepsy (TRE), respectively, and 11 autopsy controls were immunostained for Ki-67. Total number of Ki-67-positive cells (KiPC) in each hippocampal area was counted. Selected cases were further studied with double immunohistochemical labeling. KiPC were observed in all three groups. Total numbers of KiPC were significantly higher in AHS cases than in controls, but were not significantly different between TRE cases and controls. Significant differences were observed in the dentate gyrus, the cornu ammonis (CA)-4 region, and the fissura hippocampi between the AHS and control groups. In double immunolabeling, nestin was positive in some KiPC. The existence of neurogenesis/gliogenesis was shown in the hippocampi of pediatric patients with AHS. Increased numbers of progenitor cells in the hippocampi with AHS appear not to be due to seizures per se, but to be more associated with the specific cause of epilepsy.

Rai1 deficiency in mice causes learning impairment and motor dysfunction, whereas Rai1 heterozygous mice display minimal behavioral phenotypes.

Smith-Magenis syndrome (SMS) is associated with an approximately 3.7 Mb common deletion in 17p11.2 and characterized by its craniofacial and neurobehavioral abnormalities. The reciprocal duplication leads to dup(17)(p11.2p11.2) associated with the Potocki-Lupski syndrome (PLS), a neurological disorder whose features include autism. Retinoic acid induced 1 (RAI1) appears to be responsible for the majority of clinical features in both SMS and PLS. Mouse models of these syndromes harboring an approximately 2 Mb chromosome engineered deletion and duplication, respectively, displayed abnormal locomotor activity and/or learning deficits. To determine the contribution of RAI1 in the neurobehavioral traits in SMS, we performed a battery of behavioral tests on Rai1 mutant mice and the Df(11)17-1/+ mice that have a small deletion of approximately 590 kb. The mice with the small deletion were hypoactive like the large deletion mice and they also showed learning deficits. The Rai1+/- mice exhibited normal locomotor activity. However, they had an abnormal electroencephalogram with overt seizure observed in a subset of mice. The few surviving Rai1-/- mice displayed more severe neurobehavioral abnormalities including hind limb clasping, overt seizures, motor impairment and context- and tone-dependant learning deficits. X-gal staining of the Rai1+/- mice suggests that Rai1 is predominantly expressed in neurons of the hippocampus and the cerebellum. Our results suggest that Rai1 is a critical gene in the central nervous system functioning in a dosage sensitive manner and that the neurobehavioral phenotype is modified by regulator(s) in the approximately 590 kb genomic interval, wherein the major modifier affecting the craniofacial penetrance resides.

Sudden death in toddlers associated with developmental abnormalities of the hippocampus: a report of five cases.

Sudden unexplained death in childhood (SUDC) is the sudden death of a child older than 1 year of age that remains unexplained after review of the clinical history, circumstances of death, and autopsy with appropriate ancillary testing. We report here 5 cases of SUDC in toddlers that we believe define a new entity associated with hippocampal anomalies at autopsy. All of the toddlers died unexpectedly during the night, apparently during sleep. Within 48 hours before death, 2 toddlers had fever, 3 had a minor upper respiratory tract infection, and 3 experienced minor head trauma. There was a history of febrile seizures in 2 (40%) and a family history of febrile seizures in 2 (40%). Hippocampal findings included external asymmetry and 2 or more microdysgenetic features. The incidence of certain microdysgenetic features was substantially increased in the temporal lobes of these 5 cases compared with the temporal lobes of 39 (control) toddlers with the causes of death established at autopsy (P < 0.01). We propose that these 5 cases define a potential subset of SUDC whose sudden death is caused by an unwitnessed seizure arising during sleep in the anomalous hippocampus and producing cardiopulmonary arrest. Precipitating factors may be fever, infection, and/or minor head trauma. Suggested risk factors are a history of febrile seizures and/or a family history of febrile seizures. Future studies are needed to confirm these initial findings and to define the putative links between sudden death, hippocampal anomalies, and febrile seizures in toddlers.

Severe, fetal-onset form of olivopontocerebellar hypoplasia in three sibs: PCH type 5?

We present three siblings with a precise onset of fetal seizure-like activity who had severe olivopontocerebellar hypoplasia (OPCH) and degeneration. Autopsies at 20, 27, and 37 weeks gestation showed diffuse central nervous system volume loss that was most marked for the cerebellum and brain stem structures. Neuropathological abnormalities included dysplastic, C-shaped inferior olivary nuclei, absent or immature dentate nuclei, and cell paucity more marked for the cerebellar vermis than the hemispheres. Delayed development was seen in layer 2 of the cerebral cortex and in Purkinje cells of the cerebellum. Prenatal monitoring defined a developmental window of 16-18 weeks gestation when ultrasonic assessment of cerebellar width was used for prenatal diagnosis. We discuss our findings in the context of the differential diagnosis for infantile (O)PCH and propose a classification scheme for the pontocerebellar hypoplasias. These patients represent the earliest reported with OPCH and provide unique information regarding the developmental neuropathology of this condition.

Schimke immuno-osseous dysplasia: a cell autonomous disorder?

SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like protein 1) encodes a SWI/SNF ATP-dependent chromatin remodeling protein. Mutations in SMARCAL1 cause the autosomal-recessive multisystem disorder Schimke immuno-osseous dysplasia (SIOD); this suggests that the SMARCAL1 protein is involved in the development or maintenance of multiple organs. Disease within these many tissues could arise by a cell autonomous or a cell non-autonomous mechanism. Consistent with a cell autonomous mechanism, we did not find any disease recurrence in transplanted organs or protection of other tissues by the organ grafts. In order to better understand the role of SMARCAL1 during normal development and in the pathogenesis of SIOD, we characterized the spatial and temporal expression of the murine homolog (Smarcal1). The Smarcal1 mRNA and protein were expressed throughout development and in all tissues affected in patients with SIOD including the bone, kidney, thymus, thyroid, tooth, bone marrow, hair, eye, and blood vessels. Significantly, the expression profile of Smarcal1 in the mouse has led us to reexamine and identify novel pathology in our patient population resulting in changes in the clinical management of SIOD. The expression of Smarcal1 in affected tissues and the non-recurrence of disease in grafted organs lead us to hypothesize a cell autonomous function for SMARCAL1 and to propose tissue-specific mechanisms for the pathophysiology of SIOD.

Activation of mammalian target of rapamycin in cytomegalic neurons of human cortical dysplasia.

OBJECTIVE: The cortex of patients with cortical dysplasia contains several abnormal cell types. Among the dysplastic cells, cytomegalic neurons are known to be electrically hyperactive and may contribute to epileptic activity. In this study, we sought to identify molecular markers of cytomegalic neurons in focal or hemispheric cortical dysplasia and to determine whether the activity of the mammalian target of rapamycin (mTOR) kinase is abnormally high in these cells. METHODS: Microarray analysis of gene expression in large dysplastic cells microdissected from cortical dysplasia surgical specimens was used to identify markers of cytomegalic neurons. Immunohistochemistry and immunofluorescence analysis of cortical sections was used to validate the microarray results and to probe the activity of mTOR in cytomegalic neurons using phospho-specific antibodies directed against known mTOR targets. RESULTS: We demonstrate that the neurofilament heavy chain is a reliable marker of cytomegalic neurons and that targets of the mTOR kinase, such as the ribosomal protein S6, eIF4G, and Akt, are hyperphosphorylated in these dysplastic neurons. INTERPRETATION: We conclude that mTOR kinase hyperactivation is a molecular mechanism underlying the development of cytomegalic neurons. This finding may lead to the development of novel therapeutic approaches for childhood epilepsy associated with cortical dysplasia.

Secretin receptor-deficient mice exhibit impaired synaptic plasticity and social behavior.

Secretin is a peptide hormone released from the duodenum to stimulate the secretion of digestive juice by the pancreas. Secretin also functions as a neuropeptide hormone in the brain, and exogenous administration has been reported to alleviate symptoms in some patients with autism. We have generated secretin receptor-deficient mice to explore the relationship between secretin signaling in the brain and behavioral phenotypes. Secretin receptor-deficient mice are overtly normal and fertile; however, synaptic plasticity in the hippocampus is impaired and there are slightly fewer dendritic spines in the CA1 hippocampal pyramidal cells. Furthermore, secretin receptor-deficient mice show abnormal social and cognitive behaviors. These findings suggest that the secretin receptor system has an important role in the central nervous system relating to social behavior.

Transgenic mice expressing CUG-BP1 reproduce splicing mis-regulation observed in myotonic dystrophy.

Myotonic dystrophy type I (DM1) is an RNA-mediated disease caused by a non-coding CTG repeat expansion. A key feature of the RNA-mediated pathogenesis model for DM is the disrupted splicing of specific pre-mRNA targets. A link has been established between splicing regulation by CUG-BP1, a member of the CELF family of proteins, and DM1 pathogenesis. To determine whether increased CUG-BP1 function was sufficient to model DM, transgenic mice overexpressing CUG-BP1 (MCKCUG-BP1) in heart and skeletal muscle, two tissues affected in DM1, were generated. Histological and electron microscopic analyses of skeletal muscle reveal common pathological features with DM tissues: chains of central nuclei, degenerating fibers and centralized NADH reactivity. MCKCUG-BP1 mice have disrupted splicing of three CELF target pre-mRNAs, cardiac troponin T (Tnnt2), myotubularin-related 1 gene (Mtmr1) and the muscle-specific chloride channel (Clcn1), consistent with that observed in DM heart and skeletal muscle. The results are consistent with a mechanism for DM pathogenesis in which expanded repeats result in increased CUG-BP1 activity and/or other CELF family members and have trans-dominant effects on specific pre-mRNA targets.