Linking axonal degeneration to microtubule remodeling by spastin mediated microtubule severing. (2005 Feb)
linking axonal degeneration to microtubule remodeling by spastin mediated microtubule severing . mutations in the AAA adenosine triphosphatase ( atpase ) spastin ( SPG4 ) cause an autosomal dominant form of hereditary spastic paraplegia , which is a retrograde axonopathy primarily characterized pathologically by the degeneration of long spinal neurons in the corticospinal tracts and the dorsal columns . using recombinant spastin , we find that six mutant forms of spastin , including three disease associated forms , are severely impaired in atpase activity . In contrast to a mutation designed to prevent adenosine triphosphate ( ATP ) binding , an ATP hydrolysis deficient spastin mutant predicted to remain kinetically trapped on target proteins decorates microtubules in transfected cells . analysis of disease associated missense mutations shows that some more closely resemble the canonical hydrolysis mutant , whereas others resemble the ATP binding mutant . using real time imaging , we show that spastin severs microtubules when added to permeabilized , cytosol depleted cells stably expressing GFP tubulin . using purified components , we also show that spastin interacts directly with microtubules and is sufficient for severing . these studies suggest that defects in microtubule severing are a cause of axonal degeneration in human disease .

Spastin , the protein mutated in autosomal dominant hereditary spastic paraplegia , is involved in microtubule dynamics. (2002 Jan)
spastin , the protein mutated in autosomal dominant hereditary spastic paraplegia , is involved in microtubule dynamics . hereditary spastic paraplegia ( HSP ) is characterized by progressive weakness and spasticity of the lower limbs , caused by the specific degeneration of the corticospinal tracts , the longest axons in humans . Most cases of the autosomal dominant form of the disease are due to mutations in the SPG4 gene , which encodes spastin , an atpase belonging to the AAA family . The cellular pathways in which spastin operates and its role in causing degeneration of motor axons are currently unknown . By expressing wild type or atpase defective spastin in several cell types , we now show that spastin interacts dynamically with microtubules . spastin association with the microtubule cytoskeleton is mediated by the N terminal region of the protein , and is regulated through the atpase activity of the AAA domain . expression of all the missense mutations into the AAA domain , which were previously identified in patients , leads to constitutive binding to microtubules in transfected cells and induces the disappearance of the aster and the formation of thick perinuclear bundles , suggesting a role of spastin in microtubule dynamics . consistently , wild type spastin promotes microtubule disassembly in transfected cells . these data suggest that spastin may be involved in microtubule dynamics similarly to the highly homologous microtubule severing protein , katanin . impairment of fine regulation of the microtubule cytoskeleton in long …

Characterization of a novel spg3a deletion in a french canadian family. (2007 Jul)
characterization of a novel spg3a deletion in a french canadian family . hereditary spastic paraplegias ( HSPs ) are characterized by progressive lower limb spasticity and weakness . mutations in the spg3a gene , which encodes the large guanosine triphosphatase atlastin , are the second most common cause of autosomal dominant hereditary spastic paraplegia . In a large spg3a screen of 70 hereditary spastic paraplegia subjects , a novel in frame deletion , p . del436n , was identified . characterization of this deletion showed that it affects neither the guanosine triphosphatase activity of atlastin nor interactions between atlastin and spastin . interestingly , immunoblot analysis of lymphoblasts from affected patients demonstrated a significant reduction in atlastin protein levels , supporting a loss of function disease mechanism .

Hereditary spastic paraparesis : disrupted intracellular transport associated with spastin mutation. (2003 Dec)
hereditary spastic paraparesis : disrupted intracellular transport associated with spastin mutation . The commonest cause of hereditary spastic paraplegia ( HSP ) is mutation in the spastin gene . Both the normal function of spastin in the central nervous system and the mechanism by which mutation in spastin causes axonal degeneration are unknown . One hypothesis is that mutant spastin disrupts microtubule dynamics , causing an impairment of organelle transport on the microtubule network , which leads to degeneration in the distal parts of long axons . To study this neuronal and non neuronal cells were transfected with either wild type or mutant spastin proteins . We demonstrated evidence of a transient interaction of wild type spastin with microtubules , with resulting disassembly of microtubules , supporting a role for wild type spastin as a microtubule severing protein . mutant spastin demonstrated an abnormal interaction with microtubules , colocalizing with but no longer severing microtubules . The abnormal interaction of mutant spastin with microtubules was demonstrated to be associated with an abnormal perinuclear clustering of mitochondria and peroxisomes , suggestive of an impairment of kinesin mediated intracellular transport . Our findings indicate that an abnormal interaction of mutant spastin with microtubules , which disrupts organelle transport on the microtubule cytoskeleton , is likely to be the primary disease mechanism in HSP caused by missense mutations in the spastin gene .

Recent advances in hereditary spastic paraplegia. (2001 Jul)
recent advances in hereditary spastic paraplegia . The hereditary spastic paraplegias are a group of rare disorders that are characterized by great clinical and genetic heterogeneity . there has been an exponential increase in the number of HSP loci mapped in recent years , with nine out of the 17 loci reported during the past 2 years . eight loci have now been identified for the autosomal dominant form , and seven of these are associated with pure HSP . spastic paraplegia 4 remains the most frequent locus , and is usually associated with a pure phenotype . although the corresponding spastin gene was only recently identified , over 50 mutations have been described to date , which renders molecular diagnosis difficult . Five loci are known for autosomal recessive HSP , and four of these are associated with complex forms , all with different phenotypes . Two genes have been identified : paraplegin and sacsin . finally , three loci have been identified in X linked HSP , two of which are complex forms . The genes that encode L1 and PLP were the first to be identified in HSP disorders . surprisingly , the five genes encode proteins of different families , making understanding and diagnosis of HSP even more difficult . The discovery of new genes should hopefully help to clarify the pathophysiology of these disorders .

Mutations in a newly identified gtpase gene cause autosomal dominant hereditary spastic paraplegia. (2001 Nov)
mutations in a newly identified gtpase gene cause autosomal dominant hereditary spastic paraplegia . The hereditary spastic paraplegias ( HSPs ; strümpell lorrain syndrome , MIM number 18260 ) are a diverse class of disorders characterized by insidiously progressive lower extremity spastic weakness ( reviewed in refs . 1 3 ) . eight autosomal dominant HSP ( adhsp ) loci have been identified , the most frequent of which is that linked to the SPG4 locus on chromosome 2p22 ( found in approximately 42 ) , followed by that linked to the spg3a locus on chromosome 14q11 q21 ( in approximately 9 ) . Only SPG4 has been identified as a causative gene in adhsp . Its protein ( spastin ) is predicted to participate in the assembly or function of nuclear protein complexes . Here we report the identification of mutations in a newly identified gtpase gene , spg3a , in adhsp affected individuals .

A novel missense mutation ( i344k ) in the spg4gene in a korean family with autosomal dominant hereditary spastic paraplegia. (2002 Aug)
A novel missense mutation ( i344k ) in the spg4gene in a korean family with autosomal dominant hereditary spastic paraplegia . hereditary spastic paraplegia ( HSP ) is a group of clinically and genetically heterogeneous neurodegenerative disorders characterized by slowly progressive spasticity and weakness of the lower extremities . among eight loci linked with autosomal dominant ( AD ) HSP , the SPG4 locus on chromosome 2p22 accounts for about 40 of all patients . recently , mutations in a new member of the AAA protein family , called spastin , have been identified as responsible for SPG4 linked AD HSP . Here , we describe a novel missense mutation ( c . 1031t A ; i344k ) in exon 7 of the SPG4 gene identified in a korean family with typical clinical features of pure AD HSP . The mutation affects the third amino acid of the highly conserved AAA cassette domain , which is the most fore part of the domain altered by a missense mutation reported so far . clinical presentations of affected individuals carrying the i344k mutation were not different from those of pure AD HSP with SPG4 mutations reported previously . however , it is noteworthy that neither urinary dysfunction nor involvement of upper extremities was noticed in this family . To our knowledge , this is the first report of genetically confirmed AD HSP in korea .

Prenatal diagnosis of autosomal dominant hereditary spastic paraplegia ( SPG4 ) using direct mutation detection. (2004 May)
prenatal diagnosis of autosomal dominant hereditary spastic paraplegia ( SPG4 ) using direct mutation detection . objective : To present a report on prenatal diagnosis using direct SPG4 gene analysis in a family with autosomal dominant hereditary spastic paraplegia ( AD HSP ) . methods : genetic linkage and haplotype analysis were previously carried out with chromosome 2p markers . DNA was obtained from affected individuals , the affected father , the mother , and fetal DNA from an ongoing pregnancy by chorionic villus sampling ( CVS ) in the first trimester . The spastin gene ( SPG4 ) was completely sequenced . results : A novel 832insgdelaa frameshift mutation , predicted to cause loss of functional protein , was identified in the affected father and in the fetal DNA . conclusions : This is the first report on direct prenatal diagnosis of chromosome 2p linked AD HSP ( SPG4 ) . In addition , we report a novel SPG4 combined small insertion / deletion mutation in exon 5 , which may be the first SPG4 mutational hot spot .

A novel mutation in the spastin gene in a family with spastic paraplegia. (2002 May)
A novel mutation in the spastin gene in a family with spastic paraplegia . hereditary spastic paraplegia ( HSP ) is a degenerative neuromuscular disease characterized by progressive lower extremity weakness , spasticity and hyperreflexia . inheritance of HSP is commonly autosomal dominant , spastin was identified as the defective gene in chromosome 2p linked autosomal dominant hereditary spastic paraplegia ( AD HSP ) . In a large american family with AD HSP , we have identified a novel spastin mutation at a splice acceptor site in intron 6 ( 1130 1 g a ) and detected a corresponding aberrant transcript generated from a cryptic splice site . This is predicted to cause a frameshift and premature truncation of the abnormal spastin protein . Our data are the first to confirm that a mutation in an acceptor site in the spastin gene results in activation of a cryptic acceptor site and a translational frameshift . The clinical phenotype of this pedigree is also discussed .

An atypical intronic deletion widens the spectrum of mutations in hereditary spastic paraplegia. (2001 Jun)
An atypical intronic deletion widens the spectrum of mutations in hereditary spastic paraplegia . objective : To identify the genetic mutation responsible for autosomal dominant spastic paraplegia ( HSP ) in a large family with a pure form of the disorder . background : The disease locus in most families with HSP is genetically linked to the SPG4 locus on chromosome 2p21 p22 . Some of these families have mutations in the splice site or coding regions of the spastin gene ( spast ) . methods : linkage and mutational analyses were used to identify the location and the nature of the genetic defect causing the disorder in a large family . after the disease phenotype was linked to the SPG4 locus , all 17 coding regions and flanking intronic sequences of spast were analyzed by single strand conformation polymorphism analysis ( SSCP ) and compared between affected and normal individuals . direct sequencing and subcloning methods were used to investigate incongruous mobility shifts . results : The genomic sequence of spast showed a heterozygous four base pair deletion ( deltaat ) near the 3 splice site of exon three in all 11 affected individuals but not in 21 normal family members or in 50 unrelated controls ( 100 chromosomes ) . conclusions : This study identifies an atypical intronic microdeletion in spast that causes HSP and widens the spectrum of genetic abnormalities that cause the disorder .

The drosophila homologue of the hereditary spastic paraplegia protein , spastin , severs and disassembles microtubules. (2005 Apr)
The drosophila homologue of the hereditary spastic paraplegia protein , spastin , severs and disassembles microtubules . hereditary spastic paraplegias ( HSPs ) , a group of neurodegenerative disorders characterized by lower extremity spasticity and weakness , are most commonly caused by mutations in the spastin gene , which encodes a AAA atpase related to the microtubule severing protein katanin . A drosophila homolog of spastin ( D spastin ) was identified recently , and D spastin RNAi treated or genetic null flies show neurological defects , and protein overexpression decreases the density of cellular microtubules . elucidating spastin s function and disease mechanism will require a more detailed understanding of its structure and biochemical mechanism . Here , we have investigated the effects of D spastin , individual D spastin domains , and D spastin proteins bearing disease mutations on microtubules in cellular and in vitro assays . We show that D spastin , like katanin , displays atpase activity and uses energy from ATP hydrolysis to sever and disassemble microtubules ; disease mutations abolish or partially interfere with these activities .

Infantile hereditary spastic paraparesis due to codominant mutations in the spastin gene. (2004 Aug)
infantile hereditary spastic paraparesis due to codominant mutations in the spastin gene . The authors describe an infant with a severe spastic paraparesis caused by two codominant mutations of the spastin gene . This highlights the multiple molecular mechanisms that are likely to be involved in the molecular pathology of SPG4 and illustrates the importance of complete screening of the spastin gene in affected individuals , particularly if the index case has an unusual phenotype .

The microtubule severing protein spastin is essential for axon outgrowth in the zebrafish embryo. (2006 Sep)
The microtubule severing protein spastin is essential for axon outgrowth in the zebrafish embryo . hereditary spastic paraplegia ( HSP ) is a collection of neurological disorders characterized by developmental failure or degeneration of motor axons in the corticospinal tract and progressive lower limb spasticity . SPG4 mutations are the most common cause of autosomal dominant HSP and spastin ( the SPG4 gene product ) is a microtubule severing protein that shares homology with katanin , the microtubule severing activity of which promotes axon growth in cultured neurons . given the sequence and functional similarity between spastin and katanin , we hypothesized that spastin promotes the dynamic disassembly and remodelling of microtubules required for robust , properly directed motor axon outgrowth . To investigate this hypothesis , we cloned the zebrafish spg4 orthologue and used morpholino antisense oligonucleotides directed against the translation start site and the intron 7 8 splice donor site to knock down spastin function in the developing zebrafish embryo . reduced spg4 function caused dramatic defects in motor axon outgrowth without affecting the events driving the initial specification of motor neurones . other neuronal subtypes also exhibited a requirement for spg4 function , since spg4 knock down caused both widespread defects in neuronal connectivity and extensive CNS specific apoptosis . Our results reveal a critical requirement for spastin to promote axonal outgrowth during embryonic development , and they validate the zebrafish embryo as a novel model system to dissect the pathogenetic mechanisms underlying HSP . taken together …

Phenotype of AD HSP due to mutations in the spast gene : comparison with AD HSP without mutations. (2001 Jan)
phenotype of AD HSP due to mutations in the spast gene : comparison with AD HSP without mutations . background : Pure autosomal dominant hereditary spastic paraparesis ( AD HSP ) is clinically and genetically heterogeneous . there are at least seven genetic loci with varying ages at onset and disability . The spast gene at the SPG4 locus on chromosome 2p is the major disease gene for AD HSP . objectives : To investigate whether there are distinct clinical features among families with AD HSP due to spast mutations compared with families excluded from SPG4 . methods : nineteen families with pure AD HSP were identified , and the clinical features of family members were compared using a standard protocol . With use of genetic studies , the families were divided into two groups for comparison : those with mutations in spast , the mutation positive group , and those excluded from SPG4 on the basis of linkage studies , the SPG4 excluded group . results : twenty nine individuals from four families had mutations in spast , whereas 22 individuals from three families comprised the SPG4 excluded group ; in 11 families , the pattern of linkage was unknown . In the one remaining family , no mutations were found despite strong linkage to SPG4 . different mutations were identified in the four spast pedigrees , but the clinical picture was similar in each . comparison of the mutation positive group with the SPG4 excluded group revealed an …

Novel mutations in spastin gene and absence of correlation with age at onset of symptoms. (2000 Nov)
novel mutations in spastin gene and absence of correlation with age at onset of symptoms . autosomal dominant hereditary spastic paraplegia is genetically heterogeneous , with at least five loci identified by linkage analysis . recently , mutations in spastin were identified in SPG4 , the most common locus for dominant hereditary spastic paraplegia that was previously mapped to chromosome 2p22 . We identified five novel mutations in the spastin gene in five families with SPG4 mutations from north america and tunisia and showed the absence of correlation between the predicted mutant spastin protein and age at onset of symptoms .

A large family with hereditary spastic paraparesis due to a frame shift mutation of the spastin ( SPG4 ) gene … (2001 Nov)
A large family with hereditary spastic paraparesis due to a frame shift mutation of the spastin ( SPG4 ) gene : association with multiple sclerosis in two affected siblings and epilepsy in other affected family members . hereditary spastic paraparesis ( HSP ) is a clinically and genetically heterogeneous neurodegenerative disorder characterised by progressive lower limb spasticity and weakness . Some forms have been associated with white matter lesions and complex phenotypes . This study was prompted by the diagnosis of multiple sclerosis ( MS ) in two sisters from a large pedigree with hereditary spastic paraparesis . twelve affected members of the extended family were examined ( MRI and EEG were carried out and evoked potentials measured in five ) , and historical information was obtained from six affected deceased persons . The inherited disease phenotype was confirmed as autosomal dominant hereditary spastic paraparesis associated with epilepsy in four affected persons . None of the extended family had evidence of MS . genetic analysis of the family has shown linkage to chromosome 2p and sequencing of the spastin gene has identified a 1406delt frameshift mutation in exon 10 . This kindred demonstrates the clinical heterogeneity of HSP associated with spastin mutations . The possible relevance of the concurrence of HSP and MS in the sib pair is discussed .

Eight novel mutations in SPG4 in a large sample of patients with hereditary spastic paraplegia. (2006 May)
eight novel mutations in SPG4 in a large sample of patients with hereditary spastic paraplegia . background : hereditary spastic paraplegia ( HSP ) is a group of genetically heterogeneous disorders characterized by progressive spasticity of the lower limbs . mutations in the SPG4 gene , which encodes spastin protein , are responsible for up to 45 of autosomal dominant cases . objective : To search for disease causing mutations in a large series of italian patients with HSP . design : samples of DNA were analyzed by direct sequencing of all exons in SPG4 . samples from a subset of patients were also analyzed by direct sequencing of all exons in spg3a , SPG6 , spg10 , and spg13 . setting : molecular testing facility in italy . patients : sixty unrelated italian patients with pure ( n 50 ) and complicated ( n 10 ) HSP . MAIN outcome measures : mutations in SPG4 , spg3a , SPG6 , spg10 , and spg13 . results : We identified 12 different mutations , 8 of which were novel , in 13 patients . No mutations of any of the other HSP genes tested were found in 15 patients with sporadic pure HSP who did not have mutations in the SPG4 gene . conclusions : The overall rate of mutation in the SPG4 gene within our sample was 22 , rising to 26 when only patients with pure HSP were considered . The negative result obtained in 15 patients without …

Mutations of SPG4 are responsible for a loss of function of spastin , an abundant neuronal protein localized in the … (2002 Dec)
mutations of SPG4 are responsible for a loss of function of spastin , an abundant neuronal protein localized in the nucleus . mutations of spastin are responsible for the most common autosomal dominant form of hereditary spastic paraplegia ( AD HSP ) , a disease characterized by axonal degeneration of corticospinal tracts and posterior columns . generation of polyclonal antibodies specific to spastin has revealed two isoforms of 75 and 80 kDa in both human and mouse tissues with a tissue specific variability of the isoform ratio . spastin is an abundant protein in neural tissues and immunolabeling experiments have shown that spastin is expressed in neurons but not in glial cells . these data indicate that axonal degeneration linked to spastin mutations is caused by a primary defect of neurons . protein and transcript analyses of patients carrying either nonsense or frameshift spastin mutations revealed neither truncated protein nor mutated transcripts , providing evidence that these mutations are responsible for a loss of spastin function . identifying agents able to induce the expression of the non mutated spastin allele should represent an attractive therapeutic strategy in this disease .

Human spastin has multiple microtubule related functions. (2005 Nov)
human spastin has multiple microtubule related functions . hereditary spastic paraplegias ( HSPs ) are neurodegenerative diseases caused by mutations in more than 20 genes , which lead to progressive spasticity and weakness of the lower limbs . The most frequently mutated gene causing autosomal dominant HSP is SPG4 , which encodes spastin , a protein that belongs to the family of atpases associated with various cellular activities ( AAAs ) . A number of studies have suggested that spastin regulates microtubule dynamics . We have studied the atpase activity of recombinant human spastin and examined the effect of taxol stabilized microtubules on this activity . We used spastin translated from the second ATG and provide evidence that this is the physiologically relevant form . We showed that microtubules enhance the atpase activity of the protein , a property also described for katanin , an AAA of the same spastin subgroup . furthermore , we demonstrated that human spastin has a microtubule destabilizing activity and can bundle microtubules in vitro , providing new insights into the molecular pathogenesis of HSP .

Investigation of mitochondrial function in hereditary spastic paraparesis. (2003 Mar)
investigation of mitochondrial function in hereditary spastic paraparesis . following the association of hereditary spastic paraparesis ( HSP ) with mutation in the paraplegin gene ( SPG7 ) and mitochondrial dysfunction , we wished to investigate whether mitochondrial dysfunction might be associated with other forms of HSP . Five cases of HSP caused by mutation in the spastin gene ( SPG4 ) and nine cases with HSP with mutation in the spastin and paraplegin genes excluded ( non SPG4 / SPG7 ) , were investigated for mitochondrial dysfunction . muscle tissue from the HSP groups and a control group was analysed histochemically and spectrophotometrically for mitochondrial dysfunction . A significant decrease in mitochondrial respiratory chain complexes I and IV was demonstrated in the non SPG4 / SPG7 group . No abnormality was detected in the SPG4 group . We therefore conclude that there is evidence for mitochondrial dysfunction in non SPG4 / SPG7 HSP . there is no evidence for mitochondrial dysfunction in the pathogenesis of spastin related HSP .