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PubMed2003

Diffusion-weighted magnetic resonance imaging and identification of the epileptogenic tuber in patients with tuberous sclerosis.

BACKGROUND: Patients with tuberous sclerosis complex and drug-resistant epilepsy may be considered candidates for epilepsy surgery. This demands the unambiguous demonstration of the epileptogenicity of one of the tubers. OBJECTIVE: To test whether diffusion-weighted magnetic resonance imaging enables differentiation of epileptogenic tubers from inert ones. METHODS: In 4 patients with clear unifocal interictal spike activity, fluid-attenuated inversion recovery and diffusion-weighted magnetic resonance imaging were performed. Apparent diffusion coefficient maps were calculated in the identified epileptogenic tuber and compared withthose in nonepileptogenic tubers and regions of normal-appearing cortex. RESULTS: A significant increase in the apparent diffusion coefficient was found in the epileptogenic tubers. Furthermore, the apparent diffusion coefficient of the nonepileptogenic tubers was significantly higher than the trace apparent diffusion coefficient of regions of normal-appearing cortex. CONCLUSION: Diffusion-weighted magnetic resonance imaging may be of clinical importance for the identification of epileptogenic tubers in patients with tuberous sclerosis and intractable epilepsy.

Brain↗
PubMed1987

The two classes of genes for the major potato tuber protein, patatin, are differentially expressed in tubers and roots.

The major potato tuber protein, patatin, is a family of 40kd glycoproteins that constitutes forty per cent of the soluble protein in tubers but is generally undetectable in other tissues. Fused rocket immunoelectro-phoresis was used to detect in roots patatin that is immunologically different from tuber patatin. Western blots of SDS-polyacrylamide gels show root patatin to have a different molecular weight distribution than tuber patatin isoforms, but immunoprecipitation of in vitro translation products shows the patatin precursors to be of similar molecular weight in both tissues. This suggests that post-translational processing may differ in tubers and roots. Northern blots show that tuber and root patatin mRNAs are of similar size, but tuber transcripts are about 100-fold more abundant. 5' S1 nuclease and primer extension mapping suggests the class of patatin transcripts expressed in roots (class II transcripts) to be a subset of patatin transcripts expressed in tubers (classes I and II). Class II patatin mRNAs differ from class I transcripts by the presence of a 22 nucleotide insertion just upstream of the initiation codon. These data demonstrate that expression of the patatin multigene family is differentially regulated in tubers and roots.

Base Sequence↗
PubMed1981

The disintegration of yam tuber gamma-glutamyl transpeptidase during tuber storage.

As an attempt to understand some aspects of the protein catabolism in the resting yam (Dioscorea rotundata) tuber with respect to the storage problems of the tuber, gamma-glutamyl transpeptidase (gamma-GTP) was isolated from healthy tubers after aerobic storage for varying periods. The molecular weight was determined by SDS-gel electrophoresis and the activity by spectrophotometry using gamma-glutamyl alpha-naphthylamide as substrate. Molecular weight and activity were plotted versus duration of the tuber storage. The molecular weight of the gamma-GTP from newly harvested tuber was 2.2 . 10(5). Both the mol. wt and activity decreased linearly with tuber storage, the two processes having approximately equal first order rate constant, 1.2 . 10(-2)/week, with a half-life of 58 weeks. High molecular weight forms of tuber gamma-GTP when dissociated and gel electrophorized gave in each case a lower molecular weight form that also had enzymic activity. A plot of the mol. wt versus the activity gave a straight line which intersected the mol. wt axis at 200000, which is the mol. wt of the smaller subunit of gamma-GTP. These results show that yam tuber gamma-GTP undergoes progressive disintegration during tuber storage and in this process the components are lost probably from the larger subunit after proteolytic cleavage and subsequent dissociation of the cleaved components.

Drug Stability↗
PubMed1997

Giant cells in cortical tubers in tuberous sclerosis showing synaptophysin-immunoreactive halos.

We describe a characteristic pattern of immunoreactivity for synaptophysin in tuberous sclerosis. We analyzed cortical tubers from surgical specimens taken from six patients with tuberous sclerosis, which were obtained by surgical resections for the treatment of intractable seizures. The cortical tubers were characterized by blurred lamination of the cerebral cortex, hypercellularity, and gliotic changes. Neuropil in the cortex of cortical tubers showed reduced immunoreactivity for synaptophysin in all patients. 'Giant cells' were investigated in the cortex and white matter regions of cortical tubers. Some 'giant cells' had neuronal characteristics such as Nissl substance, a centrally placed chromatin-marginated nucleus, prominent nucleolus, positive immunoreactivity for microtubule-associated protein 2, and negative immunoreactivity for glial fibrillary acidic protein. Other 'giant cells' were indeterminate in cell type because they lacked Nissl bodies, distinct nucleolus, consistent immunoreactivity for microtubule-associated protein 2 and glial fibrillary acidic protein. Almost all 'neuronal giant cells' and some of the 'indeterminate giant cells' in the white matter showed intense immunoreactivity for synaptophysin: cell borders were surrounded by an intense immunoreactive halo. In conclusion, these immunohistochemical patterns for synaptophysin assist in characterizing these abnormal cells in the cortical tubers of patients with tuberous sclerosis.

Cerebral Cortex↗
PubMed2000

Magnetic resonance spectroscopy of tubers in patients with tuberous sclerosis.

OBJECTIVE: The histological features of cortical tubers in patients with tuberous sclerosis (TS) were studied by the proton magnetic resonance spectroscopy (MRS). MATERIAL AND METHODS: The subjects were 4 children, mean age of 10 years, with clear evidence of tubers on MRI and SPECT. Four age-matched control children served as control subjects. Spectra were acquired over the tuber using short TE. RESULTS: The myoinositol/creatine ratios in the tubers of TS patients were significantly increased compared with those of the control subjects (P < 0.02). The NAA/creatine ratios in the tubers of patients were significantly decreased (P < 0.02). CONCLUSIONS: The decrease of NAA/creatine ratios in the tubers of patients was considered to reflect a reduction of cranial neurons. The increase of myoinositol/creatine ratios in the tubers was thought to reflect an increase of glial cells. Proton MRS might play a role in estimation of histological changes in the neurological diseases.

Adult↗
PubMed2006

Overexpression of a bacterial 1-deoxy-D-xylulose 5-phosphate synthase gene in potato tubers perturbs the isoprenoid metabolic network: implications for the control of the tuber life cycle.

Potato tubers were engineered to express a bacterial gene encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS) in order to investigate the effects of perturbation of isoprenoid biosynthesis. Twenty-four independent transgenic lines out of 38 generated produced tubers with significantly elongated shape that also exhibited an early tuber sprouting phenotype. Expression analysis of nine transgenic lines (four exhibiting the phenotype and five showing a wild-type phenotype) demonstrated that the phenotype was strongly associated with dxs expression. At harvest, apical bud growth had already commenced in dxs-expressing tubers whereas in control lines no bud growth was evident until dormancy was released after 56-70 d of storage. The initial phase of bud growth in dxs tubers was followed by a lag period of approximately 56 d, before further elongation of the developing sprouts could be detected. Thus dxs expression results in the separation of distinct phases in the dormancy and sprouting processes. In order to account for the sprouting phenotype, the levels of plastid-derived isoprenoid growth regulators were measured in transgenic and control tubers. The major difference measured was an increase in the level of trans-zeatin riboside in tubers at harvest expressing dxs. Additionally, compared with controls, in some dxs-expressing lines, tuber carotenoid content increased approximately 2-fold, with most of the increase accounted for by a 6-7-fold increase in phytoene.

Abscisic Acid↗
PubMed2000

Changes in GA 20-oxidase gene expression strongly affect stem length, tuber induction and tuber yield of potato plants.

Gene StGA20ox1 encoding potato GA 20-oxidase is expressed to relatively high levels in leaves and regulated by daylength. To investigate whether this gene is involved in photoperiodic regulation of tuber formation, we have obtained transgenic potato plants expressing sense and antisense copies of the StGA20ox1 cDNA. Over-expression of this cDNA resulted in taller plants that required a longer duration of a short day photoperiod (SD) to tuberize. Tubers from these plants had a decreased time of dormancy and developed sprouts with elongated internodes. Plants expressing antisense copies of the StGA20ox1 cDNA had shorter stems, a decreased length of the internodes and tuberized earlier than control plants, showing increased tuber yields. Antisense inhibition of this gene had no visible effect on the time of dormancy of the tubers, although at the end of dormancy these formed sprouts with shortened internodes. Decreased levels of endogenous GA20 and GA1 were detected in the apex and first leaves of the antisense lines. These results demonstrate the involvement of the GA 20-oxidase activity encoded by StGA20ox1 in the control of stem elongation and in tuber induction but not in tuber dormancy, indicating that the latter may be regulated by another member of the gene family.

DNA, Complementary↗
PubMed1984

Fine structure of cortical tubers in tuberous sclerosis: a Golgi study.

The fine structure of cerebral cortex, including cortical tubers, was studied in 3 patients with tuberous sclerosis. Tubers were found to consist of two predominant cell populations, astroglia and small multipolar (stellate) neurons. Both cell types tended to form aggregates within tubers, with glia more prominent in the subpial region. The stellate neurons of tubers had beaded or varicose dendrites with few dendritic spines. The findings suggest that neurons within tubers are an aberrant primitive cell type that fails to express the pyramidal cell shape and dendritic morphology that is characteristic of normal human neocortex. Cortex intervening between tubers had basically normal dendritic morphology. However, quantitative study showed a decrease in the length of dendritic branches of pyramidal neurons, as also observed in several other conditions manifested by mental retardation.

Astrocytes↗
PubMed2006

Cyst-like cortical tubers in patients with tuberous sclerosis complex: MR imaging with the FLAIR sequence.

BACKGROUND: Tuberous sclerosis complex (TSC) is an inherited disorder characterized by the presence of cortical tubers, the majority of which are solid and show high signal on FLAIR images. Low-signal tubers are less frequent. OBJECTIVE: To evaluate cystic cortical tubers in patients with TSC on the basis of their appearance on FLAIR images. MATERIALS AND METHODS: MR examinations of 73 patients were retrospectively reviewed and 17 children (aged 25 days to 12.3 years) with a typical cyst-like tubers were selected for further analysis. The age of the patients, the number of lesions, and the shape and MR intensity were analyzed. RESULTS: Cyst-like cortical tubers were detected in 82% of children below 7 years of age and in 18% of those older then 7 years (P=0.00086). Most of the cystic lesions were of the shrunken type (72%), the expansile type being less frequently seen (28%). CONCLUSIONS: FLAIR images confirm the cystic character of some of the cortical tubers in TSC patients although the pathogenesis of cystic change is still unknown.

Cerebral Cortex↗
PubMed2006

Mental retardation and relation to seizure and tuber burden in tuberous sclerosis complex.

In patients with tuberous sclerosis complex (TSC), the high rates of mental retardation are associated with cortical tubers, seizure activity, and genetic factors. The goal of the study was to investigate the relationship between bilateral cortical tubers and seizure variables and mental retardation in individuals with TSC. The records of 27 patients with TSC (age 6 months to 33 years) undergoing neuropsychological assessment and the following clinical variables were examined: bilateral versus non-bilateral cortical tubers, the age of seizure onset, and presence of infantile spasms. Results were statistically analyzed. Bilateral cortical tubers (p=0.02) and early age of seizure onset (p=0.04) were significantly related to impaired cognitive functioning. Only one of the seven patients with normal cognitive functioning had bilateral tubers, whereas 13/21 patients with intellectual impairment had bilateral tubers. Patients with normal cognitive functioning experienced a mean age of seizure onset after 6 years. A trend was observed between infantile spasms and cognitive functioning (p=0.06); the lack of statistical significance likely reflects the small sample size. Neither age nor gender was related to cognitive status. Further investigation incorporating additional neuroimaging factors, antiepileptic treatment effects, and genetic variables, is needed.

Adolescent↗
PubMed2004

The relation of infantile spasms, tubers, and intelligence in tuberous sclerosis complex.

BACKGROUND: The aetiology of the learning difficulty in tuberous sclerosis is debated. It may be related to the amount of tubers in the brain or caused by the infantile spasms that occur in early life. AIMS: To examine the relative contributions to final intelligence (IQ) made by both cerebral tubers and infantile spasms. METHODS: As part of an epidemiological study of tuberous sclerosis in the south of England, patients were recruited who were able to undergo magnetic resonance imaging (MRI) without the need for an anaesthetic. Epilepsy history was determined by interview and review of clinical records. IQ was assessed using either Wechsler intelligence scales or Raven's matrices. RESULTS: A total of 41 patients consented to have an MRI scan. IQ scores were normally distributed about a mean of 91. Twenty six patients had a positive history of epilepsy, and 11 had suffered from infantile spasms. There was a significant relation between the number of tubers and IQ. Infantile spasm status partly confounded the relation between tubers and IQ, but did not render the relation statistically insignificant. The relation between infantile spasms and learning difficulty remained strong even when controlling for the number of tubers.

Adolescent↗
PubMed1999

Co-localization of TSC1 and TSC2 gene products in tubers of patients with tuberous sclerosis.

Two genes, mutations in which result in the phenotype of tuberous sclerosis (TSC), have recently been cloned. TSC2 on chromosome 16p13.3 encodes the protein tuberin, which appears to have growth regulating properties. TSC1 on chromosome 9q34 encodes hamartin which, as yet, has no specified cellular functions. Polyclonal antibodies were raised to synthetic peptides representing portions of tuberin and hamartin and used in immunoblots and immunohistochemical studies to localize the proteins in surgically resected neocortical tubers from four TSC patients. On Western blots of autopsy brain specimens, K-562 cell, and NT2 lysates, each antibody labelled a single band at the expected molecular weight. In immunohistochemical protocols on paraffin embedded tissue, antibodies to both tuberin and hamartin prominently labelled atypical and dysmorphic neuroglial cells that are a defining feature of TSC tubers. Some abnormal cells within cortical tuber sections were labelled with both tuberin and hamartin antisera. Our results suggest that tuberin and hamartin are both robustly expressed in similar populations of neuroglial cells of TSC tubers, even in the presence of TSC1 or TSC2 germline mutations. The roles of these gene products in normal and abnormal cortical development, tuber pathogenesis and the generation of seizures remain to be defined.

Adolescent↗
PubMed2004

Molecular pathogenesis of tuber formation in tuberous sclerosis complex.

Tuberous sclerosis complex results from mutations in the TSC1 (hamartin) and TSC2 (tuberin) genes. Tubers are cortical developmental malformations in patients with tuberous sclerosis complex that are associated with intractable epilepsy and are composed of histologically distinct cell types, including giant cells and dysplastic neurons. We recently showed that tubers can be dynamic lesions characterized by populations of cells undergoing proliferation, migration, and death. We demonstrate that there is cell-specific activation of the mammalian target of rapamycin (mTOR)/p70S6 kinase/ribosomal S6 cascade in tubers and that giant cells express activated (phosphorylated) p70S6 kinase and ribosomal S6 protein. These findings support impaired hamartin- and tuberin-mediated mTOR pathway regulation. Tubers likely form by constitutive activation of the mTOR cascade during brain development as a consequence of impaired hamartin or tuberin function.

Brain↗
PubMed2001

Tuber physiology and properties of starch from tubers of transgenic potato plants with altered plastidic adenylate transporter activity.

We showed recently that antisense plants with decreased activity of the plastidic ATP/ADP-transporter protein exhibit drastically reduced levels of starch and a decreased amylose/amylopectin ratio, whereas sense plants with increased activity of the transporter possessed more starch than wild-type plants and an increased amylose/amylopectin ratio. In this paper we investigate the effect of altered plastidic ATP/ADP-transporter protein expression on primary metabolism and granule morphology in more detail. Tuber tissues from antisense and sense plants exhibited substantially increased respiratory activity compared with the wild type. Tubers from antisense plants contained markedly increased levels of free sugars, UDP-Glc, and hexose phosphates, whereas phosphoenolpyruvate, isocitrate, ATP, ADP, AMP, UTP, UDP, and inorganic pyrophosphate levels were slightly decreased. In contrast, tubers from sense plants revealed a slight increase in adenine and uridine nucleotides and in the levels of inorganic pyrophosphate, whereas no significant changes in the levels of soluble sugars and metabolites were observed. Antisense tubers contained 50% reduced levels of ADP-Glc, whereas sense tubers contained up to 2-fold increased levels of this sole precursor for starch biosynthesis. Microscopic examination of starch grain morphology revealed that the size of starch grains from antisense tubers was substantially smaller (50%) compared with the wild type. The large starch grains from sense tubers appeared of a more angular morphology, which differed to the more ellipsoid shape of wild type grains. The results suggest a close interaction between plastidial adenylate transport and starch biosynthesis, indicating that ADP-Glc pyrophosphorylase is ATP-limited in vivo and that changes in ADP-Glc concentration determine starch yield, as well as granule morphology. Possible factors linking starch synthesis and respiration are discussed.

Adenine Nucleotides↗
PubMed1991

Antitranspirant-induced increases in leaf water potential increase tuber calcium and decrease tuber necrosis in water-stressed potato plants.

Experiments were undertaken with field-grown potato (Solanum tuberosum L.) plants to test the hypothesis that altering leaf:tuber water potential gradients within a plant subjected to low soil moisture will allow greater Ca accumulation in tubers and reverse Ca deficiency-related tuber necrosis. Antitranspirant formulations containing a wax emulsion and a spreader/sticker surfactant increased leaf water potential during a drought episode, significantly reducing the potential gradient that develops between leaf and tuber during a period of stress. Increased leaf water potential in treated plants was associated with decreased leaf Ca and increased tuber Ca. Tuber necrosis was found to be reduced in treated plants, thus increasing tuber quality.

Journal Article↗
PubMed1997

Comparative studies on potato tuber development using an in vitro tuber induction system.

A method for synchronized in vitro tuber induction in a Hungarian cultivar of Solanum tuberosum designated "Keszthelyi 855" has been developed. It was shown that in this system tuberization and stolon elongation primarily depend on the level of sucrose in the medium. The cytokinin, 6-bensylaminopurine (BAP), also enhances the efficiency of tuber formation, however, only at sucrose concentration above 4% (w/v). The synchronized plant culture provided starting material for isolation of genes specifically expressed in tuberizing Solanum species during the early stage of tuber development. In comparison with the non-tuberizing Solanum brevidens, three types of specific transcripts have been obtained by differential screening. Based on DNA sequence analysis the genes isolated code for the major tuber proteins, patatin and proteinase inhibitors.

Adenine↗
PubMed2001

Differential cellular expression of neurotrophins in cortical tubers of the tuberous sclerosis complex.

Neurotrophins and their receptors modulate cerebral cortical development. Tubers in the tuberous sclerosis complex (TSC) are characterized histologically by disorganized cortical cytoarchitecture and thus, we hypothesized that expression of neurotrophin mRNAs and proteins might be altered in tubers. Using in situ transcription and mRNA amplification to probe cDNA arrays, we found that neurotrophin-3 (NT3) and trkB mRNA expression were reduced whereas neurotrophin-4 (NT4) and trkC mRNA expression were increased in whole tuber sections. Alterations in mRNA abundance were defined in single microdissected dysplastic neurons (DNs) and giant cells (GCs). NT3 mRNA expression was reduced in GCs and trkB mRNA expression was reduced in DNs. NT4 mRNA expression was increased in DNs and trkC mRNA expression was increased in both DNs and GCs. In three patients, TSC2 locus mutations were confirmed and the mean tuberin mRNA expression levels was reduced across all nine cases. Consistent with these observations, NT3 mRNA expression was reduced but trkC mRNA expression was increased in vitro in human NTera2 neurons (NT2N) transfected with a tuberin antisense construct that reduced tuberin expression. Western analysis of tuber homogenates and computer-assisted densitometry of immunolabeled sections confirmed the neurotrophin mRNA expression data in whole sections and single neurotrophin immunoreactive cells. We conclude that alterations in NT4/trkB and NT3/trkC expression may contribute to tuber formation during brain development as downstream effects of the hamartin and tuberin pathway in TSC.

Adolescent↗
PubMed2006

Dual inversion recovery MRI helps identifying cortical tubers in tuberous sclerosis.

PURPOSE: Dual inversion-recovery imaging (DIR) has been advocated for the diagnosis of cortical lesions in epileptic patients. The role of this sequence, however, is not established in tuberous sclerosis patients. METHODS: We studied prospectively the interest of DIR sequence in four well-documented consecutive tuberous sclerosis patients with focal epilepsy. RESULTS: In all patients, the cortical tubers appeared very bright on this sequence and were well outlined compared with high resolution T2 or FLAIR imaging. In two patients, one cortical tuber was missed on T2 weighted images due to signal intensity close to the CSF. These lesions were better depicted on DIR than on FLAIR. Three cortical lesions from two patients were visualized only on DIR. CONCLUSION: DIR helped to depict cortical tubers and may have a complementary role in the MRI evaluation of tuberous sclerosis patients. There is a need to compare sensitivity of T2, FLAIR and DIR with a larger population of patients with focal epilepsies.

Adult↗