Interaction between hamartin and tuberin, the TSC1 and TSC2 gene products

Tuberous sclerosis (TSC) is an autosomal dominant disorder caused by a mutation in either the TSC1 or TSC2 tumour suppressor gene. The disease is characterized by a broad phenotypic spectrum that can include seizures, mental retardation, renal dysfunction and dermatological abnormalities. TSC2 encodes tuberin, a putative GTPase activating protein for rap1 and rab5. The TSC1 gene was recently identified and codes for hamartin, a novel protein with no significant homology to tuberin or any other known vertebrate protein. Here, we show that hamartin and tuberin associate physically in vivo and that the interaction is mediated by predicted coiled-coil domains. Our data suggest that hamartin and tuberin function in the same complex rather than in separate pathways.      

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.     

Prenatal diagnosis of the fragile X syndrome: loss of mutation owing to a double recombinant or gene conversion event at the FMR1 locus.

The fragile X syndrome, an X linked mental retardation syndrome, is caused by an expanded CGG repeat in the first exon of the FMR1 gene. In patients with an expanded repeat the FMR1 promoter is methylated and, consequently, the gene is silenced and no FMR1 protein (FMRP) is produced, thus leading to the clinical phenotype. Here we describe a prenatal diagnosis performed in a female from a fragile X family carrying a large premutation. In chorionic villus DNA of the male fetus the normal maternal CGG allele and a normal pattern on Southern blot analysis were found in combination with the FRAXAC2 and DXS297 allele of the maternal at risk haplotype. A second chorionic villus sampling was performed giving identical results on DNA analysis and, in addition, expression of FMRP was shown by immunohistochemistry. We concluded that the male fetus was not affected with the fragile X syndrome. Subsequent detailed haplotype analysis showed a complex recombination pattern resembling either gene conversion or a double crossover within a 20 kb genomic region.     

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.     

Two QTLs Located on Chromosomes 1 and 5 Modulate Different Aspects of the Performance of Mice of the B × D Ty RI Strain Series in the Morris Navigation Task

The Morris navigation task is widely used to study spatial abilities in rodents; namely, to analyze the effects of mutations in genetically engineered mice. Although quantitative and Mendelian genetic studies have shown that the variation of these abilities is partly under genetic control, little is known about these genetic factors. In order to analyze the genetic architecture of spatial navigation in mice, a wide genome scan was performed to map the QTLs that control various aspects of the performance, using the RI strain methodology. Latencies to locate the submerged platform across learning sessions and performance to the spatial probe test were analyzed in the 26 strains of the B × D RI series. Both cluster analysis of behavioral measurements and QTL mapping confirmed previous data showing that the escape latencies and the spatial bias rely on two distinct components of the task, controlled by different loci. A QTL on chromosome 1 influenced escape latencies during the four training sessions, whereas another QTL, located on chromosome 5, was shown to control spatial performance at the probe trial and also exhibited epistatic interactions with two other QTLs on chromosomes 2 and 13. The function of these QTLs is examined in the broader context of hippocampal-dependent learning processes and in relation to QTLs already found in similar positions in other behavioral traits.     

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.