The exocyst is an effector for Sec4p, targeting secretory vesicles to sites of exocytosis.
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Polarized secretion requires proper targeting of secretory vesicles to specific sites on the plasma membrane. Here we report that the exocyst complex plays a key role in vesicle targeting. Sec15p, an exocyst component, can associate with secretory vesicles and interact specifically with the rab GTPase, Sec4p, in its GTP-bound form. A chain of protein-protein interactions leads from Sec4p and Sec15p on the vesicle, through various subunits of the exocyst, to Sec3p, which marks the sites of exocytosis on the plasma membrane. Sec4p may control the assembly of the exocyst. The exocyst may therefore function as a rab effector system for targeted secretion. (+info)
The Caenorhabditis elegans sex determination gene mog-1 encodes a member of the DEAH-Box protein family.
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In the Caenorhabditis elegans hermaphrodite germ line, the sex-determining gene fem-3 is repressed posttranscriptionally to arrest spermatogenesis and permit oogenesis. This repression requires a cis-acting regulatory element in the fem-3 3' untranslated region; the FBF protein, which binds to this element; and at least six mog genes. In this paper, we report the molecular characterization of mog-1 as well as additional phenotypic characterization of this gene. The mog-1 gene encodes a member of the DEAH-box family. Three mog-1 alleles possess premature stop codons and are likely to be null alleles, and one is a missense mutation and is likely to retain residual activity. mog-1 mRNA is expressed in both germ line and somatic tissues and appears to be ubiquitous. The MOG-1 DEAH-box protein is most closely related to proteins essential for splicing in the yeast Saccharomyces cerevisiae, but splicing appears to occur normally in a mog-1-null mutant. In addition to its involvement in the sperm-oocyte switch and control of fem-3, zygotic mog-1 is required for robust germ line proliferation and for normal growth during development. We suggest that mog-1 plays a broader role in RNA regulation than previously considered. (+info)
Identification of DNA polymorphisms associated with the V type alpha1-antitrypsin gene.
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alpha1-Antitrypsin (alpha1-AT) is a highly polymorphic protein. The V allele of alpha1-AT has been shown to be associated with focal glomerulosclerosis (FGS) in Negroid and mixed race South African patients. To identify mutations and polymorphisms in the gene for the V allele of alpha1-AT in five South African patients with FGS nephrotic syndrome DNA sequence analysis and restriction fragment length polymorphisms of the coding exons were carried out. Four of the patients were heterozygous for the BstEII RFLP in exon III [M1(Val213)(Ala213)] and one patient was a M1(Ala213) homozygote. The mutation for the V allele was identified in exon II as Gly-148 (GGG)-->Arg (AGG) and in all patients was associated with a silent mutation at position 158 (AAC-->AAT). The patient who was homozygous for (Ala213) also had a silent mutation at position 256 in exon III (GAT-->GAC) which was not present in any of the other four patients. Although the V allele of alpha1-AT is not associated with severe plasma deficiency, it may be in linkage disequilibrium with other genes on chromosome 14 that predispose to FGS. Furthermore, the associated silent mutation at position 158 and the Ala213 polymorphism are of interest, as these could represent an evolutionary intermediate between the M1(Ala213) and M1(Val213) subtypes. (+info)
Expression of vascular endothelial growth factor in human oral squamous cell carcinoma: its association with tumour progression and p53 gene status.
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AIMS: To correlate vascular endothelial growth factor (VEGF) expression in oral squamous cell carcinoma with the clinicopathological characteristics and prognosis; and to assess whether p53 gene status is associated with VEGF expression in human cancers. METHODS: Tumour specimens from 45 patients with oral squamous cell carcinomas were examined. Expression of VEGF was determined using an immunohistochemical method, and a tumour was considered positive when more than 5% of the neoplastic cells showed VEGF immunoreactivity. The p53 gene status was screened using a polymerase chain reaction--single strand conformation polymorphism analysis. RESULTS: VEGF positive staining was detected in 19 (42.2%) of the 45 cases. VEGF immunoreactivity did not correlate with the histological degree of tumour differentiation, clinical stages, or lymph node metastasis. The patients with VEGF positive tumours had a significantly worse prognosis than those with VEGF negative tumours. The five year overall survival rate of the VEGF negative patients was 76.5%, as compared with 48.8% for the VEGF positive patients. No significant association between VEGF expression and the p53 gene status of the tumours was found. CONCLUSIONS: VEGF is a good prognostic indicator of the survival of patients with oral squamous cell carcinoma. The p53 gene status does not seem to be associated with VEGF expression in these cancers. (+info)
Three-dimensional structure of a recombinant gap junction membrane channel.
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Gap junction membrane channels mediate electrical and metabolic coupling between adjacent cells. The structure of a recombinant cardiac gap junction channel was determined by electron crystallography at resolutions of 7.5 angstroms in the membrane plane and 21 angstroms in the vertical direction. The dodecameric channel was formed by the end-to-end docking of two hexamers, each of which displayed 24 rods of density in the membrane interior, which is consistent with an alpha-helical conformation for the four transmembrane domains of each connexin subunit. The transmembrane alpha-helical rods contrasted with the double-layered appearance of the extracellular domains. Although not indicative for a particular type of secondary structure, the protein density that formed the extracellular vestibule provided a tight seal to exclude the exchange of substances with the extracellular milieu. (+info)
Genomic organization of the KCNQ1 K+ channel gene and identification of C-terminal mutations in the long-QT syndrome.
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The voltage-gated K+ channel KVLQT1 is essential for the repolarization phase of the cardiac action potential and for K+ homeostasis in the inner ear. Mutations in the human KCNQ1 gene encoding the alpha subunit of the KVLQT1 channel cause the long-QT syndrome (LQTS). The autosomal dominant form of this cardiac disease, the Romano-Ward syndrome, is characterized by a prolongation of the QT interval, ventricular arrhythmias, and sudden death. The autosomal recessive form, the Jervell and Lange-Nielsen syndrome, also includes bilateral deafness. In the present study, we report the entire genomic structure of KCNQ1, which consists of 19 exons spanning 400 kb on chromosome 11p15.5. We describe the sequences of exon-intron boundaries and oligonucleotide primers that allow polymerase chain reaction (PCR) amplification of exons from genomic DNA. Two new (CA)n repeat microsatellites were found in introns 10 and 14. The present study provides helpful tools for the linkage analysis and mutation screening of the complete KCNQ1 gene. By use of these tools, five novel mutations were identified in LQTS patients by PCR-single-strand conformational polymorphism (SSCP) analysis in the C-terminal part of KCNQ1: two missense mutations, a 20-bp and 1-bp deletions, and a 1-bp insertion. Such mutations in the C-terminal domain of the gene may be more frequent than previously expected, because this region has not been analyzed so far. This could explain the low percentage of mutations found in large LQTS cohorts. (+info)
Aldosterone excretion rate and blood pressure in essential hypertension are related to polymorphic differences in the aldosterone synthase gene CYP11B2.
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Significant correlation of body sodium and potassium with blood pressure (BP) may suggest a role for aldosterone in essential hypertension. In patients with this disease, the ratio of plasma renin to plasma aldosterone may be lower than in control subjects and plasma aldosterone levels may be more sensitive to angiotensin II (Ang II) infusion. Because essential hypertension is partly genetic, it is possible that altered control of aldosterone synthase gene expression or translation may be responsible. We compared the frequency of 2 linked polymorphisms, one in the steroidogenic factor-1 (SF-1) binding site and the other an intronic conversion (IC), in groups of hypertensive and normotensive subjects. In a larger population, the relationship of aldosterone excretion rate to these polymorphisms was also evaluated. In 138 hypertensive subjects, there was a highly significant excess of TT homozygosity (SF-1) over CC homozygosity compared with a group of individually matched normotensive control subjects. The T allele was significantly more frequent than the C allele in the hypertensive group compared with the control group. Similarly, there was a highly significant relative excess of the conversion allele over the "wild-type" allele and of conversion homozygosity over wild-type homozygosity in the hypertensive group compared with the control group. In 486 subjects sampled from the North Glasgow Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) population, SF-1 and IC genotypes were compared with tetrahydroaldosterone excretion rate. Subjects with the SF-1 genotypes TT or TC had significantly higher excretion rates than those with the CC genotype. The T allele was associated with higher excretion rates than the C allele. However, no significant differences were found in excretion rate between subjects of different IC genotype. Urinary aldosterone excretion rate may be a useful intermediate phenotype linking these genotypes to raised BP. However, no causal relationship has yet been established, and it is possible that the polymorphisms may be in linkage with other causative mutations. (+info)
The optically determined size of exo/endo cycling vesicle pool correlates with the quantal content at the neuromuscular junction of Drosophila larvae.
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According to the current theory of synaptic transmission, the amplitude of evoked synaptic potentials correlates with the number of synaptic vesicles released at the presynaptic terminals. Synaptic vesicles in presynaptic boutons constitute two distinct pools, namely, exo/endo cycling and reserve pools (). We defined the vesicles that were endocytosed and exocytosed during high K+ stimulation as the exo/endo cycling vesicle pool. To determine the role of exo/endo cycling vesicle pool in synaptic transmission, we estimated the quantal content electrophysiologically, whereas the pool size was determined optically using fluorescent dye FM1-43. We then manipulated the size of the pool with following treatments. First, to change the state of boutons of nerve terminals, motoneuronal axons were severed. With this treatment, the size of exo/endo cycling vesicle pool decreased together with the quantal content. Second, we promoted the FM1-43 uptake using cyclosporin A, which inhibits calcineurin activities and enhances endocytosis. Cyclosporin A increased the total uptake of FM1-43, but neither the size of exo/endo cycling vesicle pool nor the quantal content changed. Third, we increased the size of exo/endo cycling vesicle pool by forskolin, which enhances synaptic transmission. The forskolin treatment increased both the size of exo/endo cycling vesicle pool and the quantal content. Thus, we found that the quantal content was closely correlated with the size of exo/endo cycling vesicle pool but not necessarily with the total uptake of FM1-43 fluorescence by boutons. The results suggest that vesicles in the exo/endo cycling pool primarily participate in evoked exocytosis of vesicles. (+info)