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[Interaction between the enhancers of yellow and the yellow gene in Drosophila melanogaster].

Earlier, mutations at six loci designated enhancers of yellow (e(y)1-6) were obtained in the system of prolonged instability, where transpositions of Stalker mobile element occur. These mutations decrease pigmentation of the cuticle in a number of alleles. In the present work, genetic analysis of the mechanism of action of e(y)1u1, e(y)3u1 and newly described e(y)7u1 mutations on the yellow locus expression was conducted. The data are obtained proving that the enhancers of yellow 1 and 3 control transcription of the yellow locus. At the same time, the interaction of here described gene e(y)7 with the yellow gene is likely to occur at the level of protein products.

Alleles↗

[Long QT syndrome].

Romano-Ward syndrome, one of familial long QT syndromes, is an inherited disorder that causes sudden death from cardiac arrhythmias, specifically torsade de pointes and ventricular fibrillation. By linkage analyses, three LQT loci were previously mapped: LQT1 on chromosome 11p15.5, LQT2 on 7q35-36, LQT3 on 3p21-24. It was recently brought to light that LQT2 and LQT3 were caused by mutations of the gene encoding cardiac ion channels. Mutations in HERG on chromosome 7q35-36, encoding potassium channels (Ikr), cause LQT2, and block of Ikr is a known mechanism for drug-induced prolongation of cardiac action potentials, which provides a mechanistic link between LQT2 and certain forms of acquired LQT. Mutations in SCN5A on chromosome 3p21, encoding the human heart voltage-gated sodium-channel alpha-subunit, cause LQT3. Mutant channels show a sustained inward sodium current during membrane depolarization, which explains prolongation of cardiac action potentials.

Animals↗

Menstrual disorders and infertility caused by inactivating mutations of the luteinizing hormone receptor gene.

OBJECTIVE: To review clinical findings, hormone levels, and DNA analyses in genetic males and females with inactivating mutations of the LH receptor gene. DESIGN: Review of reported cases. SETTING: A university hospital. PATIENT(S): Genetic males and females with inactivating mutations of the LH receptor gene. RESULT(S): The clinical presentation in genetic males ranged from female genitalia to male genitalia with micropenis caused by Leydig cell hypoplasia. Genetic females presented with amenorrhea or oligomenorrhea, enlarged cystic ovaries, and infertility. Both males and females had elevated LH levels and LH/FSH ratios. Sequencing of genomic DNA revealed homozygous or compound heterozygous deletions, nonsense mutations, or missense mutations in the LH receptor gene. CONCLUSION(S): This study of patients with inactivating mutations of the LH receptor indicates that in genetic males, the action of hCG and LH is necessary for the normal development of primary and secondary sexual characteristics. In contrast, secondary sexual characteristics develop in genetic females in the absence of LH action, but they fail to ovulate.

Female↗

Expression of the parathyroid hormone-related peptide gene in retinoic acid-induced differentiation: involvement of ETS and Sp1.

Differentiation of P19 embryonal carcinoma (EC) and embryonal stem (ES)-5 cells with retinoic acid (RA) induces expression of PTH-related peptide (PTHrP) mRNA. In this study we have characterized a region between nucleotide (nt) -88 and -58 relative to the transcription start site in the murine PTHrP gene that was involved in this expression. Sequence analysis identified two partially overlapping binding sites for the Ets family of transcription factors and an inverted Sp1-binding site. Two major specific bands were detected in a bandshift assay using an oligonucleotide spanning nt -88 and -58 as a probe and nuclear extracts from both undifferentiated and RA-differentiated P19 EC cells. The lower complex consisted of Ets-binding proteins as demonstrated by competition with consensus Ets-binding sites, while the upper complex contained Sp1-binding activity as demonstrated by competition with consensus Sp1-binding sites. The observed bandshift patterns using nuclear extracts of undifferentiated or RA-differentiated P19 cells were indistinguishable, suggesting that the differentiation-mediated expression was not caused by the induction of expression of new transcription factors. Mutations in either of the Ets-binding sites or the Sp1-binding site completely abolished RA-induced expression of PTHrP promoter reporter constructs, indicating that the RA effect was dependent on the simultaneous action of both Ets- and Sp1-like activities. Furthermore, these mutations also abolished promoter activity in cells that constitutively expressed PTHrP mRNA, suggesting a central role for the Ets and Sp1 families of transcription factors in the expression regulation of the mouse PTHrP gene.

Animals↗

Molecular genetics of breast cancer.

In the last two decades, molecular studies have enlightened the complexity of the genetic alterations that occur in breast cancer cells. To date, more than 40 different genes or loci have been found to be altered in breast carcinomas. Although some of these genes, as for example ERBB2, appear to be mutated in a high proportion of cases, their mechanism of action and their role in the different stages of cancer development are still poorly understood. More recently, two major determinants of the inherited predisposition to breast cancer, BRCA1 and BRCA2, have been isolated. As a consequence, it is now possible to screen families with a positive history of breast carcinomas for the identification of mutations carriers, in order to address these individuals into adequate programs of cancer surveillance and prevention.

Breast Neoplasms↗

[Importance of genetic recombination for the preservation and progress of species in the course of evolution].

The role of genetic recombinations is considered in the context of ecological stability of organisms. The ecological stability is taken as a special notion distinct from fitness in its original sense as the Maltusian parameter according to R. Fisher. The genetic exchange within the species provides the recovery of a species specific level of ecological stability that is lowered in particular individuals as a result of the accumulation of mutations in microevolutionary processes. It is supposed that the accumulation of the mutations that decrease organisms' ecological stability leads to the action of truncated selection. This type of selection explains the advantage of recombination in the model of A.S. Kondrashov (1982). In the evolving species, ecological stability is gradually increasing in the process of evolution as a result of hybridization between the narrow-specialized races. Genetic recombinations provide a constant DNA homogenization within the species and, therefore, the species integrity as an elementary structure responsible for the preservation and rise in the level of ecological stability of organisms in evolving lineages.

Animals↗

Lambda cin-1, a new mutation which enhances lysogenization by bacteriophage lambda, and the genetic structure of the lambda cy region.

Seven lambda cy mutants have been mapped within a small region located approximately halfway between the rightward boundary of the imm434 region and the lambda cII gene. The seven mutants lie at four sites separated by a total distance of about 12 nucleotide pairs, as estimated from recombination frequencies. Six of the seven mutants lie on the right side of the cy fine structure map, spanning a total distance of about 3-5 nucleotide pairs. Lying approximately 11-21 nucleotide pairs to the left of the leftmost cy mutant is a newly described mutation called cin-1, for c independent. The cin-1 mutation allows some lysogenization when coupled with any cy, cII or cIII mutant, but not when coupled with a defective cI gene. The cin-1 mutation, like cy mutants, has a cis-dominant action upon the cI gene in mixed infections. The observation that gammaimm434 cin-1-cy2001 lysogenizes efficiently, but not gammaimm434 cin-1 cy2001 cII68 nor any other gammaimm434 cin-1 cy derivative, is interpreted to mean that all of the cy mutants on the right side of the cy fine structure map inactivate a binding site for cII/cIII function, but that cy2001, the single mutant on the left side of the cy fine structure map, does not inactivate that binding site.

Chromosome Mapping↗

Wild type neu transgene counteracts mutant homologue in malignant transformation of rat Schwann cells.

Mutational activation of the neu (erbB-2) receptor protein tyrosine kinase gene appears to be the triggering event in the process of oncogenesis induced by N-ethyl-N-nitrosourea (EtNU) in immature Schwann cells of the rat peripheral nervous system. Subsequent loss of the wild-type neu allele may represent a critical secondary step towards malignancy. Developmentally-regulated expression of a wild-type rat neu transgene (neu cDNA under the control of the rat Po promoter) in the Schwann cells of transgenic BDIX and Sprague-Dawley rats exposed to EtNU on postnatal day 1 results in a lower incidence of early atypical proliferates in the trigeminal nerve. Furthermore, re-introduction of the wild-type neu gene into homozygous neu mutant schwannoma cells counteracts the expression of the tumorigenic phenotype. The suppressive action of the wild-type gene over its mutationally activated oncogenic homologue underlines the critical function of the neu gene in the control of differentiation in the Schwann cell lineage, and provides evidence for the responsiveness of cellular phenotypes towards quantitative shifts in the dosage of wild-type vs mutant signal transducing molecules.

Alleles↗

[Genetics and genomics of long QT syndrome].

In the past decade, molecular genetics has revealed that some life-threatening arrhythmogenic disorders, such as long QT syndrome, are due to mutated genes encoding ion channels that generate the cardiac action potential. Great efforts made in various fields have partly solved problems caused by unforeseen genetic diversity of these congenital arrhythmogenic disorders, while the genetics of these disorders has recently proved to be applicable to very wide-ranging conditions associated with sudden cardiac death, and increased knowledge about the human genome will revolutionize researches into arrhythmic diseases in future. The purpose of this review is to outline the recent advances and problems in the molecular genetics in long QT syndrome.

Death, Sudden, Cardiac↗

Characterization of in vitro and in vivo mutations in non-conserved nucleotides in the ribosomal RNA recognition domain for the ribotoxins ricin and sarcin and the translation elongation factors.

The sarcin/ricin domain in 23 S/28 S rRNA is crucial for ribosome function, since it constitutes at least part of the binding site for the elongation factors and hence is essential for binding aminoacyl-tRNA and for translocation. The domain is also the site of action of ricin and sarcin and analysis of the effect of mutations in the RNA on recognition by the cytotoxins has helped to define the structure and to understand the function of the region. We have constructed deletions, separately, of pairs of non-conserved, juxtaposed but non-hydrogen-bonded nucleotides that correspond to C4317 and C4331, and to U4316 and C4332, in an oligoribonucleotide that mimics the sarcin/ricin domain in rat 28 S rRNA. The deletions had no effect on the depurination of A4324 by ricin nor on the cleavage of the phosphodiester bond on the 3' side of G4325 by sarcin. However, simultaneous deletion of the four nucleotides decreased cleavage by sarcin but did not affect depurination by ricin. Removal of the non-canonical A4318.A4330 pair abolished recognition by both toxins. Deletion from oligoribonucleotides, that reproduce the sarcin/ricin domain of Escherichia coli 23 S rRNA, of U2653 and C2667 (equivalent to U4316, C4317 and C4331, C4332 in 28 S rRNA), or substitution of guanosine for U2653 (designed to form a Watson-Crick G2653.C2667 pair), reduced cleavage by sarcin whereas depurination by ricin was slightly increased. An increase in the stability of the mutant oligoribonucleotides may be the basis of the impairment in sarcin action. The tm for the wild-type RNA is 60 degreesC; for the double-deletion mutant U2653Delta/C2667Delta it is 65 degreesC; and for the U2653G transversion it is 69 degreesC. Expression of a mutant 23 S rRNA gene lacking U2653 and C2667 is lethal and a U2653G transversion mutation impairs growth. The mutant ribosomes are less active in protein synthesis than the wild-type and ribosomes with the U2653G mutation are resistant to sarcin. The binding of EF-G to oligoribonucleotides with a U2653/C2667 double deletion is reduced and an effect on the affinity of the factor for the sarcin/ricin domain may account in part for the decrease in ribosome efficiency. The results stress the potential importance in rRNA structure and function of non-conserved nucleotides, and suggest that the sarcin/ricin domain in ribosomes requires a region of structural flexibility for optimal efficiency.

Animals↗

TOM1p, a yeast hect-domain protein which mediates transcriptional regulation through the ADA/SAGA coactivator complexes.

The hect-domain has been characterized as a conserved feature of a group of E3 ubiquitin ligases. Here we show that the yeast hect-domain protein TOM1p regulates transcriptional activation through effects on the ADA transcriptional coactivator proteins. Null mutations of tom1 result in similar defects in transcription from ADH2 and HIS3 promoters, and enhanced transcription from the GAL10 promoter as do null mutations in ngg1/ada3. Strains with disruptions of both ngg1 and tom1 have the same phenotype as strains with a disruption of only ngg1 implying that these genes are acting through the same pathway. In the absence of TOM1p, the normal associations of the ADA proteins with SPT3p and the TATA-binding protein are reduced. The action of TOM1p is most likely mediated through ubiquitination since mutation of Cys3235 to Ala, corresponding residues of which are required for thioester bond formation with ubiquitin in other hect-domain proteins, results in similar changes in transcription as the null mutation. A direct role for TOM1p in regulation of ADA-associated proteins is further supported by the finding that SPT7p is ubiquitinated in a TOM1p-dependent fashion and that TOM1p coimmunoprecipitates with the ADA proteins.

Acetyltransferases↗

UltraRapid communications : vascular superoxide production by NAD(P)H OxidaseAssociation with endothelial dysfunction and clinical risk factors

Superoxide anion plays important roles in vascular disease states. Increased superoxide production contributes to reduced nitric oxide (NO) bioactivity and endothelial dysfunction in experimental models of vascular disease. We measured superoxide production by NAD(P)H oxidase in human blood vessels and examined the relationships between NAD(P)H oxidase activity, NO-mediated endothelial function, and clinical risk factors for atherosclerosis. Endothelium-dependent vasorelaxations and direct measurements of vascular superoxide production were determined in human saphenous veins obtained from 133 patients with coronary artery disease and identified risk factors. The predominant source of vascular superoxide production was an NAD(P)H-dependent oxidase. Increased vascular NAD(P)H oxidase activity was associated with reduced NO-mediated vasorelaxation. Furthermore, reduced endothelial vasorelaxations and increased vascular NAD(P)H oxidase activity were both associated with increased clinical risk factors for atherosclerosis. Diabetes and hypercholesterolemia were independently associated with increased NADH-dependent superoxide production. The association of increased vascular NAD(P)H oxidase activity with endothelial dysfunction and with clinical risk factors suggests an important role for NAD(P)H oxidase-mediated superoxide production in human atherosclerosis. The full text of this article is available at http://www.circresaha.org. Key Words:atherosclerosis endothelium superoxide nitric oxide diabetes Two Distinct Congenital Arrhythmias Evoked by a Multidysfunctional Na(+) Channel Marieke W. Veldkamp, Prakash C. Viswanathan, Connie Bezzina, Antonius Baartscheer, Arthur A.M. Wilde, Jeffrey R. Balser Abstract-The congenital long-QT syndrome (LQT3) and the Brugada syndrome are distinct, life-threatening rhythm disorders linked to autosomal dominant mutations in SCN5A, the gene encoding the human cardiac Na(+) channel. It is believed that these two syndromes result from opposite molecular effects: LQT3 mutations induce a gain of function, whereas Brugada syndrome mutations reduce Na(+) channel function. Paradoxically, an inherited C-terminal SCN5A mutation causes affected individuals to manifest electrocardiographic features of both syndromes: QT-interval prolongation (LQT3) at slow heart rates and distinctive ST-segment elevations (Brugada syndrome) with exercise. In the present study, we show that the insertion of the amino acid 1795insD has opposite effects on two distinct kinetic components of Na(+) channel gating (fast and slow inactivation) that render unique, simultaneous effects on cardiac excitability. The mutation disrupts fast inactivation, causing sustained Na(+) current throughout the action potential plateau and prolonging cardiac repolarization at slow heart rates. At the same time, 1795insD augments slow inactivation, delaying recovery of Na(+) channel availability between stimuli and reducing the Na(+) current at rapid heart rates. Our findings reveal a novel molecular mechanism for the Brugada syndrome and identify a new dual mechanism whereby single SCN5A mutations may evoke multiple cardiac arrhythmia syndromes by influencing diverse components of Na(+) channel gating function. The full text of this article is available at http://www.circresaha.org. Key Words: Na(+) channel inactivation long-QT syndrome Brugada syndrome

Journal Article↗

Two distinct congenital arrhythmias evoked by a multidysfunctional Na(+) channel.

The congenital long-QT syndrome (LQT3) and the Brugada syndrome are distinct, life-threatening rhythm disorders linked to autosomal dominant mutations in SCN5A, the gene encoding the human cardiac Na(+) channel. It is believed that these two syndromes result from opposite molecular effects: LQT3 mutations induce a gain of function, whereas Brugada syndrome mutations reduce Na(+) channel function. Paradoxically, an inherited C-terminal SCN5A mutation causes affected individuals to manifest electrocardiographic features of both syndromes: QT-interval prolongation (LQT3) at slow heart rates and distinctive ST-segment elevations (Brugada syndrome) with exercise. In the present study, we show that the insertion of the amino acid 1795insD has opposite effects on two distinct kinetic components of Na(+) channel gating (fast and slow inactivation) that render unique, simultaneous effects on cardiac excitability. The mutation disrupts fast inactivation, causing sustained Na(+) current throughout the action potential plateau and prolonging cardiac repolarization at slow heart rates. At the same time, 1795insD augments slow inactivation, delaying recovery of Na(+) channel availability between stimuli and reducing the Na(+) current at rapid heart rates. Our findings reveal a novel molecular mechanism for the Brugada syndrome and identify a new dual mechanism whereby single SCN5A mutations may evoke multiple cardiac arrhythmia syndromes by influencing diverse components of Na(+) channel gating function. The full text of this article is available at http://www.circresaha.org.

Arrhythmias, Cardiac↗

Modulation of membrane currents by cyclic AMP in cleavage-arrested Drosophila neurons.

A number of Drosophila learning mutants have defective intracellular second-messenger systems. In an effort to develop techniques that will allow direct measurement of the effects of these mutations on whole-cell neuronal membrane currents, the perforated-patch whole-cell (PPWC) technique has been applied to cleavage-arrested cultured embryonic Drosophila neurons. This technique permits the measurement of membrane currents without disturbing the intracellular environment. As a result of the maintenance of the intracellular environment, Drosophila neuron currents are found to be much more stable than when measured using the conventional whole-cell (CWC) patch-clamp technique. Ca2+ channel currents, which typically 'wash out' within a few minutes of the beginning of CWC recording, are stable for the duration of the seal (tens of minutes) when measured using the PPWC technique. Since the learning mutations dunce and rutabaga disrupt cyclic AMP signalling, the action of externally applied dibutyryl cyclic AMP (db-cAMP) and theophylline on Ca2+ and K+ channel currents were studied. db-cAMP and theophylline enhanced the Ba2+ current, carried by Ca2+ channels, but had no effect on the K+ current in the cleavage-arrested neurons. However, the large variability and reduction in density of Ba2+ and K+ currents raise questions about the suitability of using these cleavage-arrested cells as models for Drosophila neurons.

Animals↗

[Antimutagenic effects of para-aminobenzoic acid in experiments with bacterial cells. Noninterference in the mutation process controlled by plasmid pKM101].

The dependence of expression of PABA antimutagenic action in bacterial cells on the character of genetic control of the mutagenic process was studied. PABA antimutagenic activity was largely connected with the negative control of SOS repair which is controlled by bacterial cell genes, but not by pKM101 plasmid genes. These results are in agreement with the idea that the systems of repair and mutagenesis specified by cell genome and plasmids are not identical.

4-Aminobenzoic Acid↗

Cellular components involved in the cell death induced by cisplatin in the absence of p53 activation.

Cisplatin (CDDP) is a DNA damaging agent and is widely used for treating cancer. While the role of p53 in CDDP-induced cell death has been stressed, evidence exists that CDDP can also kill p53-mutated cells. To investigate the latter mechanism, we performed a comparative study using three different human cell types, SNU-16 (a stomach cancer cell-line), U937 (a leukemic cell-line) and 293T (a kidney fibroblast cell-line), which are defective in terms of p53 activation. A focus was placed on Bcl-2 family proteins, reactive oxygen species (ROS), and mitogen-activated protein kinases. Our results suggest that the ability of CDDP to kill these cells can be mediated by JNK, p38 MAPK and ROS, but not by ERK. It was also found that CDDP can increase the ratio of pro-apoptotic/pro-survival Bcl-2 members. While the importance of these components was found to depend on cell type, JNK was commonly involved in the deaths of all cell types examined. Therefore, the JNK pathway appears to be an ideal target for the modulation of the lethal action of CDDP in multiple types of p53-mutated cells.

Antineoplastic Agents↗

Determinants of NPC1 expression and action: key promoter regions, posttranscriptional control, and the importance of a "cysteine-rich" loop.

Mutations in the NPC1 gene cause Niemann-Pick type C disease, which is characterized by the accumulation of free cholesterol and other lipids in lysosomes. The NPC1 glycoprotein is located in a late endosomal compartment that transiently interacts with lysosomes. To identify factors regulating NPC1 expression and action, we analyzed the function of the human NPC1 promoter in human-derived ovarian, hepatic, and neuronal cells. A fragment containing the first 208 base pairs upstream from the major transcription initiation site was sufficient to drive near maximal NPC1 promoter activity. Deletion analysis revealed that sequences between base pairs -111 and -37 play an important role in controlling NPC1 transcription. Treatment of proliferating granulosa cells with 30 microM progesterone, which induces a reversible phenocopy of the cholesterol trafficking defect of Niemann-Pick type C disease, increased NPC1 mRNA levels threefold. The protein synthesis inhibitor, cycloheximide, also increased NPC1 mRNA levels, augmenting the progesterone-induced increase in NPC1 mRNA abundance. Progesterone treatment was shown to increase the mRNA half-life, but did not affect NPC1 promoter activity. Cysteine residues in a "cysteine-rich" loop predicted to reside in the intralumenal compartment of vesicles containing NPC1 were mutated, resulting in proteins that were incapable of correcting the cholesterol trafficking defect in CT60 cells, a Chinese hamster cell line in which the endogenous NPC1 gene is inactivated. Converting isoleucine 1061, also predicted to lie within the cysteine-rich loop, to a threonine residue inactivated the protein as well. The I1061T mutation is one of the most common mutations in Niemann-Pick type C disease. All of the cysteine-rich loop mutants were localized to cholesterol-engorged lysosomes in a pattern mimicking the distribution of NPC1 in progesterone-treated cells. A recombinant protein representing the cysteine-rich loop was shown to bind to a zinc-NTA agarose column. We conclude: (1) that cis elements residing in the first 111 base pairs upstream from the transcription start site are critical for transcription of the NPC1 gene; (2) that NPC1 expression is subject to posttranscriptional regulation in response to treatments that disrupt NPC1 function; and (3) that an intralumenal cysteine-rich loop with zinc-binding activity is critical to NPC1's ability to unload lysosomal cargo.

Animals↗

Isoform variable action among thyroid hormone receptor mutants provides insight into pituitary resistance to thyroid hormone.

Resistance to thyroid hormone (RTH) is due to mutations in the beta-isoform of the thyroid hormone receptor (TR-beta). The mutant TR interferes with the action of normal TR to cause the clinical syndrome. Selective pituitary resistance to thyroid hormone (PRTH) results in inappropriate TSH secretion and peripheral sensitivity to elevated thyroid hormone levels. Association of the PRTH phenotype with in vitro behavior of the mutant TR has proved elusive. Alternative exon utilization results in two TR-beta isoforms, TR-beta 1 and TR-beta 2, which differ only in their amino termini. Although the TR-beta 1 isoform is ubiquitous, the TR-beta 2 isoform is found predominantly in the anterior pituitary and brain. To date, in vitro evaluation of RTH mutations has focused on the TR-beta 1 isoform. Site-directed mutagenesis was used to create several PRTH (R338L, R338W, V349M, R429Q, I431T) and generalized RTH (delta 337T, P453H) mutations in both TR-beta isoforms. The ability of mutant TRs to act as dominant negative inhibitors of wild type TR-beta function on positive and negative thyroid hormone response elements (pTREs and nTREs, respectively) was evaluated in transient transfection assays. PRTH mutants had no significant dominant negative activity as TR-beta 1 isoforms on pTREs found in peripheral tissues or on nTREs found on genes regulating TSH synthesis. PRTH mutants, in contrast, had strong dominant negative activity on these same nTREs as TR-beta 2 isoforms. Cotransfected retinoid X receptor-alpha was required for negative T3 regulation via the TR-beta 1 isoform but was not necessary for negative regulation via the TR-beta 2 isoform in CV-1 cells. The differing need for retinoid X receptor cotransfection demonstrates two distinct negative T3-regulatory pathways, one mediated by the TR-beta 1 and the other mediated by TR-beta 2. The selective effect of PRTH mutations on the TR-beta 2 isoform found in the hypothalamus and pituitary vs. the TR-beta 1 isoform found in peripheral tissues suggests a molecular mechanism for the PRTH disorder.

Alleles↗