The TSC1 gene product, hamartin, negatively regulates cell proliferation

Tuberous sclerosis is an autosomal dominant hereditary disease caused by mutations in either the TSC1 or the TSC2 tumor suppressor gene. The TSC1 gene on chromosome 9q34 encodes a 130 kDa protein named hamartin, and the TSC2 gene on chromosome 16p13.3 codes for tuberin, a 200 kDa protein. Here we show that expression of hamartin, assayed by immunoblot analyses, is high in G(0)-arrested cells and hamartin is expressed throughout the entire ongoing cell cycle. An interaction of hamartin and tuberin can be detected in every phase of the cell cycle. Ectopic expression of high levels of hamartin attenuates cellular proliferation. We provide evidence that this effect could depend on a coiled-coil region earlier proposed to be involved in binding of hamartin to tuberin. Further investigations revealed that hamartin affects cell proliferation via deregulation of G(1) phase. Our data have a clear impact on understanding the role of hamartin during development of this disease.     

Analysis of behavioral and hippocampal variation in congenic albino and pigmented BALB mice

Mice of the BALB/c strain are widely used in behavioral research in spite of the albino condition, which can obscure brain-behavior relationships. We have developed a pigmented BALB strain, congenic to BALB/c, which could be more appropriate for neurogenetic studies that aim at identifying the effects of neurological mutations on behavior. Comparison of inbred albino and pigmented congenic BALB arising from the same litters provides a valuable tool for detecting the consequences of the albino mutation on behavioral performances. Preliminary results presented here show that the albino condition does not interfere with the development and patterns of connectivity of mossy fibers in the hippocampus. On the other hand, obvious coat color-linked differences appear for locomotor activity and defecation scores in the open field, pigmented mice being unexpectedlyl less active and more reactive than albino, as if better vision increased their reactions to a novel, anxiogenic environment. Finally, pigmented mice do not show better performances in the radial maze, which confirms that the inability of BALB mice for spatial learning in a highly demanding version of this task cannot be attributed to their inability to process visual information.     

Morphometric study of the human fetal heart. I. Arterial segment

This study measured the dimensions of the great arteries of normal human fetal hearts at an early fetal stage (between 13-20 weeks post-fertilization) in 103 fetuses obtained by necropsy. Different segments of the aorta and the pulmonary artery were dissected and their external diameters measured under stereoscopic magnification. All segments showed linear growth during this period of fetal development. Ranges in median values of external diameters associated with the pulmonary artery were: 2.1-4.2 mm for the valve ring; 2.2-4.2 mm for the main pulmonary trunk; 1.2-2.5 mm for the right pulmonary artery; 0.9-2.18 mm for the left pulmonary artery; and 4.0-8.0 mm for the length of the main pulmonary trunk. Similarly, in the aorta, median diameters were: 2.1-4.2 mm for the ascending aorta; 1.92-3.8 mm for the aortic arch; 1.45-3.0 mm for the aortic isthmus; and 1.75 -3.35 mm for the descending aorta. The diameter of the ductus arteriosus ranged between 1.2-2.45 mm. The growth rates of the pulmonary artery and the aorta were similar. The diameter of the ascending aorta was found to be greater than that of the descending aorta and the right pulmonary artery was wider than the left pulmonary artery. In addition, the magnitude of growth in the various aortic segments was different and the ratios obtained between the aortic isthmus and the ascending and descending aortae, ranged between 0.66-0.93. This study provides important morphometric reference information concerning the dimensions and growth of the great arteries of the fetal heart and has clinical application in pediatric cardiac surgery and echocardiography.     

Identification of a large insertion and two novel point mutations (3671del8 and S1221X) in tuberous sclerosis complex (TSC) patients. Mutations in brief no. 119. Online

Important symptoms of tuberous sclerosis complex (TSC), an autosomal dominant disorder, are hamartomata in several organs, mental retardation and epilepsy. Either one of two loci can be involved (TSC1 and TSC2), of which the TSC2 gene has been cloned. To date, only 35 mutations in the TSC2 gene have been described ranging from large deletions to point mutations. Southern blot analysis using cDNA clones of the TSC2 gene was performed on a cohort of 160 unrelated TSC patients and revealed a 10 kb insertion. The insertion was also present in DNA of the affected father. Both patients showed renal angiomyolipoma, hypomelanotic macules and epilepsy. SSCP analysis of exons 1,2,3,9,12,14,30a and 36 identified two mutations in exon 30a: 3671del8 and S1221X. Symptoms of the sporadic patient with the 3671del8 mutation are cortical tubers, subependymal nodules, facial angiofibroma, ungual fibroma, renal angiomyolipoma, hypomelanotic macules, epilepsy and mental retardation. Clinical symptoms of the patient with the S1221X mutation are facial angiofibroma, ungual fibroma, hypomelanotic macules, epilepsy and mental retardation. His parents were negative for the S1221X mutation, although a germline mosaicism can not be excluded. Besides the previously described polymorphism 1596C->T, two rare variants were observed, a substitution of C->T at position 1294 and at position 1299 C->A.     

Family studies of the steroid 21-hydroxylase and coplement C4 genes define 11 haplotypes in classical congenital adrenal hyperplasia in The Netherlands

Two steroid 21-hydroxylase genes are normally present within the human major histocompatibility complex near the genes encoding the fourth component of complement (C4A and C4B). Steroid 21-hydroxylase is encoded by the CYP21 gene, while the highly homologous CYP21P gene is a pseudogene. We studied steroid 21-hydroxylase and complement C4 haplotypes in 33 Dutch patients (29 families) suffering form classical congenital adrenal hyperplasia (CAH) and in their 80 family members, and also in 55 unrelated healthy controls, using 21-hydroxylase and complement C4 cDNA probes. Eleven different haplotypes, defined in terms of gene deletions, gene duplications, conversions of CYP21 to CYP21P, and long and short C4 genes, were found. In 23% of the patients' haplotypes, the CYP21 gene was deleted; in 12%, it was converted into a CYP21P pseudogene. In the remaining 65%, the defect was apparently caused by a mutation not detectable by this method. The most common haplotype (with one CYP21 and one CYP21P gene) was significantly more often observed in patients with simple virilizing CAH than in those with salt-losing CAH. Comparison of the 21-hydroxylase haplotypes found in CAH patients from several countries shows evidence for considerable genetic variation between the groups studied.     

How Thick Is Thick? Multicenter Study of the Rheological and Material Property Characteristics of Mealtime Fluids and Videofluoroscopy Fluids

Objective rheological assessment of fluids given to dysphagic patients at mealtime and during videofluoroscopy was carried out using a multicenter format. Thin, quarter-thick, half-thick and full-thick fluids were examined for the degree of correlation between mealtime fluids and their allegedly matched videofluoroscopy counterparts. The study was carried out to determine whether perceived subjective differences between mealtime fluids and videofluoroscopy fluids could be quantified using the rheological parameters of viscosity, density, and yield stress. The results showed poor correlation between mealtime fluids and videofluoroscopy fluids over all parameters. In general, the videofluoroscopy fluids were more viscous, more dense, and showed higher yield stress values than their mealtime counterparts. Given these results, it is reasonable to assume that the fluids used during videofluoroscopy do not provide an accurate indication of swallowing ability at mealtime. Therefore, it is suggested that clinicians use objective methods to rheologically match videofluoroscopy fluids to mealtime fluids.     

Characterisation of TSC1 promoter deletions in tuberous sclerosis complex patients

Tuberous sclerosis complex (TSC), an autosomal dominant disorder, is a multisystem disease with manifestations in the central nervous system, kidneys, skin and/or heart. Most TSC patients carry a pathogenic mutation in either TSC1 or TSC2. All types of mutations, including large rearrangements, nonsense, missense and frameshift mutations, have been identified in both genes, although large rearrangements in TSC1 are scarce. In this study, we describe the identification and characterisation of eight large rearrangements in TSC1 using multiplex ligation-dependent probe amplification (MLPA) in a cohort of 327 patients, in whom no pathogenic mutation was identified after sequence analysis of both TSC1 and TSC2 and MLPA analysis of TSC2. In four families, deletions only affecting the non-coding exon 1 were identified. In one case, loss of TSC1 mRNA expression from the affected allele indicated that exon 1 deletions are inactivating mutations. Although the number of TSC patients with large rearrangements of TSC1 is small, these patients tend to have a somewhat milder phenotype compared with the group of patients with small TSC1 mutations.     

Missense mutations to the TSC1 gene cause tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterised by the development of hamartomas in a variety of organs and tissues. The disease is caused by mutations in either the TSC1 gene on chromosome 9q34 or the TSC2 gene on chromosome 16p13.3. The TSC1 and TSC2 gene products, TSC1 and TSC2, interact to form a protein complex that inhibits signal transduction to the downstream effectors of the mammalian target of rapamycin (mTOR). Here we investigate the effects of putative TSC1 missense mutations identified in individuals with signs and/or symptoms of TSC on TSC1-TSC2 complex formation and mTOR signalling. We show that specific amino-acid substitutions close to the N-terminal of TSC1 reduce steady-state levels of TSC1, resulting in the activation of mTOR signalling and leading to the symptoms of TSC.     

Functional Assessment of TSC2 Variants Identified in Individuals with Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in the TSC1 or TSC2 genes. The TSC1 and TSC2 gene products, TSC1 and TSC2, form a complex that inhibits the mammalian target of rapamycin (mTOR) complex 1 (TORC1). Here, we investigate the effects of 78 TSC2 variants identified in individuals suspected of TSC, on the function of the TSC1–TSC2 complex. According to our functional assessment, 40 variants disrupted the TSC1–TSC2‐dependent inhibition of TORC1. We classified 34 of these as pathogenic, three as probably pathogenic and three as possibly pathogenic. In one case, a likely effect on splicing as well as an effect on function was noted. In 15 cases, our functional assessment did not agree with the predictions of the SIFT amino acid substitution analysis software. Our data support the notion that different, nonterminating TSC2 mutations can have distinct effects on TSC1–TSC2 function, and therefore, on TSC pathology.     

Transient enriched housing before amyloidosis onset sustains cognitive improvement in Tg2576 mice

Levels of educational and occupational attainment, as components of cognitive reserve, may modify the relationship between the pathological hallmarks and cognition in Alzheimer's disease (AD). We examined whether exposure of a Tg2576 transgenic mouse model of AD to environmental enrichment (EE) at a specific period during the amyloidogenic process favored the establishment of a cognitive reserve. We found that exposure to EE during early adulthood of Tg2576 mice—before amyloidogenesis has started—reduced the severity of AD-related cognitive deficits more efficiently than exposure later in life, when the pathology is already present. Interestingly, early-life exposure to EE, while slightly reducing forebrain surface covered by amyloid plaques, did not significantly impact aberrant inhibitory remodeling in the hippocampus of Tg2576 mice. Thus, transient early-life exposure to EE exerts long-lasting protection against cognitive impairment during AD pathology. In addition, these data define the existence of a specific life time frame during which stimulatory activity most efficiently builds a cognitive reserve, limiting AD progression and favoring successful aging.