RESUMO
BACKGROUND: Obesity is an important risk-stratifying co-morbidity for many pathological conditions. Controversy exists about its influence in outcomes after acute pancreatitis (AP). This study assessed abdominal fat distribution (subcutaneous, retroperitoneal and intra-abdominal) measured using computer tomography (CT) images and related it to outcomes in patients with AP. METHODS: The case notes of patients admitted with AP were identified from computerised records from 2008 to the 2013. Image analysis software was used to assess the individual abdominal fat distributions from CT images. RESULTS: A total of 79 patients were included. There was no relationship between fat distribution and either severity of, or mortality from, AP. Fat distribution was not found to be an independent risk factor on multivariate analysis. There was, however, a positive correlation between retroperitoneal and intra-abdominal fat with APACHE II scores, Ranson and Glasgow score and Multiple Organ Dysfunction score (MODS) on various days following admission (r = 0.421, p = 0.0008; r = 0.469, p < 0.0001; r = 0.398, p = 0.007; r = 0.336, p = 0.011, respectively). On multiple logistical regression analysis, the only variables associated with mortality were Balthazar Severity Index, MODS and EWS with a p value of <0.0001, 0.0019 and 0.0481, respectively. CONCLUSIONS: Obese patients have worse predicted outcomes as measured by the EWS, MODS and Ranson scores. Abdominal fat distribution, however, was not shown to be directly related to AP severity or mortality. The addition of fat parameters may be of use in prognostic CT severity index models, but from this data, it does not appear to be an independent risk factor of adverse outcome.
Assuntos
Gordura Abdominal/diagnóstico por imagem , Adiposidade , Pancreatite/complicações , Pancreatite/diagnóstico por imagem , Doença Aguda , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Obesidade/complicações , Pancreatite/mortalidade , Prognóstico , Estudos Retrospectivos , Fatores de Risco , Índice de Gravidade de Doença , Tomografia Computadorizada por Raios X , Adulto JovemRESUMO
AIM: To ensure diagnostic yields were adequate in patients with suspected ureteric calculi with and without haematuria, and to assess whether there was a significant difference between these two groups in men and women. MATERIALS AND METHODS: A retrospective analysis was undertaken of 513 patient records who attended the Emergency Department with suspected ureteric colic over 8 months. RESULTS: 513 patient records were evaluated. The overall positive rate for calculi was 45.4%, with an alternative diagnosis in 14.4%. Of the patients scanned with haematuria 49.36% were positive. The positive scan rate in males was significantly higher than in females (56% v. 31%, p < 0.0001). 32.79% of patients scanned without haematuria had a proven calculus. The positive rate in males without haematuria was 40.39% versus 27.14% in females. CONCLUSION: The overall diagnostic yield of 45.4% is acceptable according to national guidelines. A large number of patients scanned without haematuria were found to have a calculus. This review suggests that in males a negative urine dipstick should not preclude CT investigation for renal colic in the presence of a "classical" history. However, the number of female patients with negative scans suggests that further randomized studies are needed to identify the ideal investigation pathway in women.
Assuntos
Assistência Ambulatorial/métodos , Hematúria/urina , Tomografia Computadorizada por Raios X/métodos , Cálculos Ureterais/diagnóstico por imagem , Cálculos Ureterais/urina , Adolescente , Adulto , Idoso , Serviço Hospitalar de Emergência , Feminino , Hematúria/complicações , Hematúria/diagnóstico , Humanos , Rim/diagnóstico por imagem , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Distribuição por Sexo , Tomografia Computadorizada por Raios X/estatística & dados numéricos , Reino Unido , Ureter/diagnóstico por imagem , Cálculos Ureterais/complicações , Adulto JovemRESUMO
INTRODUCTION: Surgical stress in the presence of fasting worsens the catabolic state, causes insulin resistance and may delay recovery. Carbohydrate rich drinks given preoperatively may ameliorate these deleterious effects. A systematic review was undertaken to analyse the effect of preoperative carbohydrate loading on insulin resistance, gastric emptying, gastric acidity, patient wellbeing, immunity and nutrition following surgery. METHODS: All studies identified through PubMed until September 2011 were included. References were cross-checked to ensure capture of cited pertinent articles. RESULTS: Overall, 17 randomised controlled trials with a total of 1,445 patients who met the inclusion criteria were identified. Preoperative carbohydrate drinks significantly improved insulin resistance and indices of patient comfort following surgery, especially hunger, thirst, malaise, anxiety and nausea. No definite conclusions could be made regarding preservation of muscle mass. Following ingestion of carbohydrate drinks, no adverse events such as apparent or proven aspiration during or after surgery were reported. CONCLUSIONS: Administration of oral carbohydrate drinks before surgery is probably safe and may have a positive influence on a wide range of perioperative markers of clinical outcome. Further studies are required to determine its cost effectiveness.
Assuntos
Carboidratos da Dieta/administração & dosagem , Complicações Pós-Operatórias/prevenção & controle , Cuidados Pré-Operatórios/métodos , Administração Oral , Bebidas , Diabetes Mellitus Tipo 2/complicações , Ácido Gástrico/fisiologia , Esvaziamento Gástrico/fisiologia , Nível de Saúde , Humanos , Imunidade/fisiologia , Resistência à Insulina/fisiologia , Estado Nutricional , Segurança do Paciente , Ensaios Clínicos Controlados Aleatórios como AssuntoRESUMO
INTRODUCTION: The terms 'enhanced recovery after surgery', 'enhanced recovery programme' (ERP) and 'fast track surgery' refer to multimodal strategies aiming to streamline peri-operative care pathways, to maximise effectiveness and minimise costs. While the results of ERP in colorectal surgery are well reported, there have been no reviews examining if these concepts could be applied safely to hepatopancreatobiliary (HPB) surgery. The aim of this systematic review was to appraise the current evidence for ERP in HPB surgery. METHODS: A MEDLINE ® literature search was undertaken using the keywords 'enhanced recovery', 'fast-track', 'peri-operative', 'surgery', 'pancreas' and 'liver' and their derivatives such as 'pancreatic' or 'hepatic'. The primary endpoint was length of post-operative hospital stay. Secondary endpoints were morbidity, mortality and readmission rate. RESULTS: Ten articles were retrieved describing an ERP. ERP protocols varied slightly between studies. A reduction in length of stay was a consistent finding following the incorporation of ERP when compared with historical controls. This was not at the expense of increased rates of readmission, morbidity or mortality in any study. CONCLUSIONS: The introduction of an ERP in HPB surgery appears safe and feasible. Currently, many of the principles of the multimodal pathway are derived from the colorectal ERP and distinct differences exist, which may impede its implementation in HPB surgery.
Assuntos
Doenças dos Ductos Biliares/cirurgia , Ductos Biliares/cirurgia , Hepatopatias/cirurgia , Fígado/cirurgia , Pâncreas/cirurgia , Pancreatopatias/cirurgia , Doenças dos Ductos Biliares/reabilitação , Protocolos Clínicos , Convalescença , Humanos , Tempo de Internação , Pancreatopatias/reabilitação , Assistência Perioperatória/métodosRESUMO
INTRODUCTION: Arteriomegaly is the diffuse ectasia of arteries with or without aneurysmal disease. Patients with arteriomegaly have a higher incidence of morbidity including limb loss compared to patients with other arteriopathies. The aim of this observational study was to review the management of these patients in our institution. METHODS: Radiologists and surgeons prospectively reviewed aortofemoral angiography. Patients with arteriomegaly were identified. Data relating to demographics, mode of presentation, risk factors, type of arteriomegaly, management and progression of disease were analysed. RESULTS: Arteriomegaly was identified in 1.3% of patients (n = 69) undergoing lower limb angiography in the study period. Of these, the majority (n = 67) were men. The mean age was 74 years (range: 60-89 years) and 76% were smokers. Co-morbidities included coronary artery disease (55%), diabetes mellitus (20%), hypertension (45%) and cerebrovascular events (6%). Forty-nine patients presented with critical limb ischaemia and eighteen patients were seen electively in the outpatients department with symptoms of intermittent claudication. Data were incomplete for two male patients and were therefore not included. At presentation, 22 patients were classified as Hollier type I, 5 were type II and 9 were type III. Thirty-one patients had arteriomegalic vessels but no aneurysmal disease. After a median follow-up duration of 76 months (range: 6-146 months), 34 patients progressed to type I, 2 to type II and 18 to type III. Thirteen remained without aneurysmal disease. Twenty-nine patients required angioplasty and twenty-eight required bypass surgery during this time. In total, 102 procedures were required for complicated disease. The limb salvage rate was 92%. Although 8 patients in our series died, the remaining 59 are under regular follow up. CONCLUSIONS: This study illustrates the progressive nature of arteriomegaly. Results of the management of these patients in our institution are similar to those in the literature. We suggest an additional fourth category to Hollier's classification that describes arteriomegalic disease without aneurysmal degeneration as this, too, deserves special management. Regular follow-up visits and early intervention for patients with arteriomegaly is advocated to reduce the high incidence of morbidity.
Assuntos
Artérias , Doenças Vasculares/terapia , Idoso , Idoso de 80 Anos ou mais , Aneurisma/classificação , Aneurisma/cirurgia , Angioplastia/métodos , Dilatação Patológica/classificação , Dilatação Patológica/cirurgia , Progressão da Doença , Feminino , Humanos , Claudicação Intermitente/etiologia , Isquemia/etiologia , Perna (Membro)/irrigação sanguínea , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Fatores de Risco , Doenças Vasculares/classificaçãoRESUMO
INTRODUCTION: Ultrasonography is used frequently to exclude significant pathology in young women presenting with non-specific lower abdominal pain (NSLAP). This study examined parameters that predicted the likelihood of significant findings on ultrasonography. These results could be used to select patients for priority imaging or identify those who could be managed with no ultrasonography. METHODS: A total of 65 women with NSLAP were identified from 283 admissions. Group 1 (n=42) consisted of patients with normal imaging. Group 2 (n=23) included patients with 'positive' scans requiring treatment. White cell count (WCC), C-reactive protein (CRP) levels, platelet count, age, duration of pain and length of stay in hospital were compared between the groups. RESULTS: The median WCC and CRP were greater in Group 2 than in Group 1: 15 x 10(9)/l and 123 mg/l versus 11 x 10(9)/l and 72 mg/l respectively (p=0.01 and p=0.05). CRP was a weak predictor of positive pathology on ultrasonography (area under curve [AUC]=0.66, p=0.027) and WCC was a strong predictor of abnormal pathology on ultrasonography (AUC=0.7, p=0.005). A WCC of >12.8 x 10(9)/l was 65% sensitive and 71% specific in predicting subsequent pathology on ultrasonography. The median wait for ultrasonography was 24 hours (range: 1-96 hours). CONCLUSIONS: This study failed to define any criteria that could select patients not requiring ultrasonography. Since ultrasonography is a relatively cheap and safe investigation, its continued use to screen women with NSLAP is justified. WCC should be used to prioritise imaging.
Assuntos
Dor Abdominal/diagnóstico por imagem , Dor Abdominal/etiologia , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Proteína C-Reativa/metabolismo , Feminino , Humanos , Tempo de Internação , Contagem de Leucócitos , Pessoa de Meia-Idade , Estudos Prospectivos , Curva ROC , Ultrassonografia , Adulto JovemRESUMO
AIMS: The term "enhanced recovery programme (ERP)" means applying defined protocols to augment the recovery of patients following surgery. Inflammation is body's response to insults such as infection, injury and surgical procedures. Inflammatory mediators whose function is initially protective may cause undesirable consequences, if the response is unnecessarily prolonged. The principle effects of ERP result from the reduction of the profound stress which results following major surgical procedures. METHODS: A Pubmed literature search was undertaken using the keywords enhanced recovery, surgery and omega-3. The primary endpoint was whether the addition of omega-3 to ERP improved morbidity and mortality. RESULTS: Nine randomised trials examining the effect of omega-3 enriched diets following surgery were analysed. Inclusion of omega-3 helps in maintaining a positive nitrogen balance, overcome immune dysfunction, lower the incidence of post-operative infections with the consequence of reduced morbidity and mortality. CONCLUSIONS: The provision of early or continuous nutrition is one of the cornerstones of an ERP. A theoretically ideal regimen would provide an energy substrate and protein and contain a component which would limit inappropriate inflammation. The beneficial role of omega-3 results from a number of effects which limit the inflammatory response, principally by influencing the production of eicosanoids and modulating cytokines. They also enhance cell-mediated immunity and preserve immune function better than standard dietary formulations. Although ERPs have already produced significant progress, there is sufficient evidence to suggest that the provision of omega-3 fatty acids may result in further improvements.
Assuntos
Ácidos Graxos Ômega-3/fisiologia , Fenômenos Fisiológicos da Nutrição , Cuidados Pós-Operatórios/métodos , Dieta , Humanos , Inflamação/fisiopatologia , Ensaios Clínicos Controlados Aleatórios como AssuntoRESUMO
INTRODUCTION: Although the pathophysiology of sepsis has been extensively studied, the disease remains a common cause of death in the critically ill patient. It thus remains one of the most pressing clinical and economic problems of modern medicine. A vast amount of inflammatory mediators have been identified as key factors in driving sepsis. Therapeutic agents designed to target these mediators have so far failed to demonstrate significant clinical benefit. METHODS: Clinical trials are the standard for assessing safety and efficacy of novel agents but are made difficult by the heterogeneous nature of septic patients. This review aims to highlight the complex nature of sepsis and the inherent difficulties encountered in designing clinical trials in these patients. The major factors contributing to the difficulties in improving internal and external validity will be discussed with the aim of guiding future study design. CONCLUSIONS: The design of clinical trials on the septic patient remains a challenge. Methodology must be rigorous if seemingly positive clinical trials which are widely implemented are later discredited as a result of poor study design. Many lessons can be learnt from the study design of the PROWESS trial, however there remains room for improvement. This review serves as a stimulus and guide in motivating much needed high quality clinical trials in sepsis.
Assuntos
Ensaios Clínicos como Assunto , Projetos de Pesquisa , Sepse/tratamento farmacológico , HumanosRESUMO
Intraductal papillary mucinous neoplasms (IPMNs) are benign cystic lesions of the pancreas with recognised premalignant potential. An occasional feature of IPMNs is fistula formation to surrounding organs. This report describes a case of a pancreaticogastric fistula from a main duct IPMN that produced the complete resolution of the patient's symptoms.
Assuntos
Carcinoma Ductal Pancreático/complicações , Fístula Gástrica/etiologia , Fístula Pancreática/etiologia , Neoplasias Pancreáticas/complicações , Idoso , Carcinoma Ductal Pancreático/diagnóstico por imagem , Feminino , Fístula Gástrica/diagnóstico por imagem , Humanos , Fístula Pancreática/diagnóstico por imagem , Neoplasias Pancreáticas/diagnóstico por imagem , Tomografia Computadorizada por Raios XRESUMO
BACKGROUND: No definitive evidence exists regarding the treatment of acute portal vein thrombosis (PVT). Treatment modalities described include conservative management, anticoagulation, thrombolysis, and thrombectomy. This review examines the impact of such treatment, its outcomes, and the complications resulting from the resultant portal hypertension. METHODS: A Medline literature search was undertaken using the keywords portal vein thrombosis, anticoagulation, thrombolysis, and thrombectomy. The primary end point was portal vein recanalization. Secondary outcome measures were morbidity and the development of portal hypertension and its sequelae, including variceal bleeding. Data from articles relating to PVT in the context of cirrhosis, malignancy, or liver transplant were excluded. RESULTS: Early systemic anticoagulation results in complete portal vein recanalization in 38.3% of cases and partial recanalization in 14.0% of cases. Spontaneous recanalization without treatment can only be expected in up to 16.7% of patients. Frequently this is only when associated with self-limiting underlying pathology and/or minimal thrombus extension. Thrombolysis can be associated with major complications in up to 60% of patients. CONCLUSIONS: The natural history of acute PVT is poorly described. Spontaneous resolution of acute portal vein thrombosis is uncommon. Early anticoagulation results in a satisfactory rate of recanalization with minimal procedure-associated morbidity. Thrombolysis should be used with caution and only considered if the disease is progressive and signs of mesenteric ischemia are present. Further well-designed trials with precise outcome reporting are needed to improve our understanding of the disease.
Assuntos
Anticoagulantes/uso terapêutico , Veia Porta , Trombose Venosa/terapia , Doença Aguda , Humanos , Hipertensão Portal/etiologia , Trombólise Mecânica , Trombectomia , Resultado do Tratamento , Trombose Venosa/etiologia , Trombose Venosa/cirurgiaRESUMO
INTRODUCTION: Sepsis is a leading cause of death in the critically ill patient. It is a heterogeneous disease and it is frequently difficult to make an unequivocal and expeditious diagnosis. The current 'gold standard' in diagnosing sepsis is the blood culture but this is only available after a significant time delay. Mortality rates from sepsis remain high, however, the introduction of sepsis care bundles in its management has produced significant improvements in patient outcomes. Central to goal-directed resuscitation is the timely and accurate diagnosis of sepsis. The rapid diagnosis and commencement of the appropriate therapies has been shown to reduce the mortality. MATERIALS AND METHODS: Biomarkers are already used in clinical practice to aid other more traditional diagnostic tests. In the absence of an adequate gold standard to diagnose sepsis, there has been considerable and growing interest in trying to identify suitable biomarkers. There is currently an unmet need in the medical literature to communicate the importance of the challenges relating to the rapid diagnosis and implementation of goal-directed therapy in sepsis and the underlying concepts that are directing these investigations. This article reviews the more novel biomarkers investigated to differentiate systemic inflammatory response syndrome from sepsis. CONCLUSION: The biomarkers described reflect the difficulties in making evidence-based recommendations particularly when interpreting studies where the methodology is of poor quality and the results are conflicting. We are reminded of our responsibilities to ensure high quality and standardised study design as articulated by the STAndards for the Reporting of Diagnostic accuracy studies (STARD) initiative.
Assuntos
Biomarcadores , Pesquisa Biomédica/normas , Síndrome de Resposta Inflamatória Sistêmica/diagnóstico , Diagnóstico Diferencial , Humanos , Sepse/diagnósticoRESUMO
OBJECTIVE: We report the case of a recurrent familial malignant carotid body tumour presenting with metastasis to local ipsilateral lymph nodes; the rarity of both recurrence combined with nodal spread is emphasised in this article. METHOD: We present a case report, and a review of the world literature concerning the diagnosis and management of carotid body tumours in the familial setting. CASE REPORT: A woman with a family history of succinate dehydrogenase complex subunit B gene mutation presented with right vocal fold palsy. A causative carotid body tumour was excised. Fifteen years later, the patient developed a right-sided swelling in the jugulo-digastric region, together with shooting pains towards her right ear. Imaging revealed right posterior triangle lymphadenopathy. Fine needle aspiration cytology of the node was equivocal. Computed tomography of her neck revealed, in addition, a mass within the right side of the larynx. Excision biopsy of the lymph node demonstrated metastatic paraganglioma. A carotid angiogram revealed a right-sided carotid body tumour. This was embolised prior to neck exploration and excision of the carotid body tumour with en bloc resection of adjacent nodes. Histological analysis confirmed the presence of lymph nodes containing metastatic paraganglioma. CONCLUSION: This case report demonstrates the need for extra vigilance to enable early disease detection in the familial setting of carotid body tumour, in order to reduce the surgical morbidity associated with disease progression. In addition, our report highlights the atypical aspects of presentation in the familial setting, together with the difficulty and lack of standardisation regarding monitoring of the disease.
Assuntos
Tumor do Corpo Carotídeo/diagnóstico , Neoplasias de Cabeça e Pescoço/diagnóstico , Paraganglioma/diagnóstico , Tumor do Corpo Carotídeo/genética , Tumor do Corpo Carotídeo/cirurgia , Diagnóstico Diferencial , Embolização Terapêutica , Feminino , Predisposição Genética para Doença , Neoplasias de Cabeça e Pescoço/genética , Neoplasias de Cabeça e Pescoço/cirurgia , Humanos , Excisão de Linfonodo , Metástase Linfática , Pessoa de Meia-Idade , Recidiva Local de Neoplasia , Paraganglioma/genética , Paraganglioma/cirurgia , Succinato Desidrogenase/genética , Paralisia das Pregas Vocais/etiologiaRESUMO
Situs inversus totalis (SIT) is a rare defect of genetic predisposition. It may cause difficulties in the diagnostic and therapeutic management of abdominal pathology due to the mirror-image anatomy. We report the management of a case of symptomatic cholelithiasis with emphasis on its surgical technique combined with a review of the literature.
Assuntos
Colecistectomia Laparoscópica/métodos , Colelitíase/cirurgia , Situs Inversus/complicações , Colecistectomia Laparoscópica/efeitos adversos , Colelitíase/complicações , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
INTRODUCTION: This study assessed the ability of gloves to simulate rheumatoid arthritis of the hand. SUBJECTS AND METHODS: Assessments were made in the dominant hand of 24 healthy volunteers with no glove, glove A (simulating stiffness only) and glove B (simulating stiffness and pain). Results were compared to data held on 23 rheumatoid arthritis patients. Sollerman score was used as a standardised measure of hand function and time taken to complete testing was recorded. Grip strength was also measured in volunteers. RESULTS: Both gloves simulate a reduction in power and prolong time taken to complete Sollerman hand-function testing. The gloves are less able to simulate a matched reduction in function when compared to rheumatoid arthritis sufferers. Sollerman score is 9.7% less in rheumatoid arthritis hands than a healthy volunteer using the glove. CONCLUSIONS: The glove could, therefore, be used to guide future design of tools and aides that accommodate for hand disorders. More work on the usefulness of such disease simulation in the design of tools for such patients is needed.
Assuntos
Artrite Reumatoide/fisiopatologia , Vestuário , Articulação da Mão/fisiopatologia , Modelos Biológicos , Atividades Cotidianas , Adulto , Idoso , Avaliação da Deficiência , Feminino , Força da Mão , Humanos , Masculino , Pessoa de Meia-Idade , Simulação de PacienteRESUMO
Chromosomal location and local chromatin structure are thought to play important roles in the stability of transgene expression. Fluorescence in situ hybridization (FISH) is a cytogenetic technique that allows the localization of specific DNA sequences on chromosomes. It provides an excellent means to analyze the chromosomal environment of integrated transgenes, helping to assess the effect of position on gene expression. FISH analyses have been conducted on nuclear chromosomal DNA at metaphase, interphase, meiotic prophase (pachytene) and on extended chromatin fibers (DNA fiber-FISH) and naked DNA molecules. Despite the small size of rice chromosomes, FISH has been successfully accomplished to detect unique and repetitive DNA sequences. A detailed FISH procedure for the detection of small and single copy transgenes within the rice genome is described and the application of FISH to evaluate chromosomal location and the local chromatin structure of transgenes as parameters that could affect their expression is discussed.
Assuntos
Hibridização in Situ Fluorescente/métodos , Oryza/genética , Transgenes , Mapeamento Cromossômico/métodos , Dosagem de GenesRESUMO
The promoter region of the rice ubiquitin2 (rubq2) gene was found to be polymorphic between japonica (T309) and indica (IR24) lines as the result of a 270-bp deletion in T309. A TTATA footprint in the T309 rubq2 promoter suggested that an excision event had occurred, and inspection of the 270-bp region present in IR24 revealed that it had all the characteristics of a miniature inverted repeat transposable element (MITE). Database searches showed that this element is a member of a new MITE family, which we have named Kiddo. Thirty-five complete Kiddo sequences were identified in existing rice genomic sequence databases. They could be arranged into four groups, within-group sequence identity was over 90%, with 65-75% identity between groups. The high sequence similarity within a group indicates that some Kiddo members were recently mobile and may still be active. An additional 24 decayed Kiddo sequences were detected. Interestingly, approximately 80% of 18 Kiddo members from annotated accessions lie within 530 bp of a coding sequence. That approximately 40% of Kiddo members present in genic regions reside in introns suggests that Kiddo transposition entails the use of both DNA and RNA intermediates, and may provide some insight into the origins of individual groups. DNA blot analysis showed that Kiddo is a rice-specific element, although one sequence with limited (72%) similarity to Kiddo group A was detected as a wheat EST. Kiddo family members may represent new molecular and phylogenetic markers, as well as representing valuable materials for studying the molecular mechanisms of MITE transposition.
Assuntos
Proteínas de Arabidopsis , Elementos de DNA Transponíveis , DNA de Plantas/análise , Oryza/genética , Sequência de Bases , Southern Blotting , Clonagem Molecular , Primers do DNA/química , Etiquetas de Sequências Expressas , Regulação da Expressão Gênica , Dados de Sequência Molecular , Filogenia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Reação em Cadeia da Polimerase , Regiões Promotoras Genéticas , Homologia de Sequência do Ácido Nucleico , Sequências Repetidas Terminais/genética , Ubiquitinas , Zea mays/genéticaRESUMO
Chromatin structure, the organized packaging of DNA with histones in the nucleus, is now seen as a dynamic fabric that changes with development. Here, we use studies on the phaseolin (phas) gene that encodes a seed protein to show how chromatin structure interacts with the transcription machinery to accomplish rigorous spatial regulation of expression. In leaf and other vegetative tissues, a nucleosome is rotationally and translationally positioned over an ensemble of three phased TATA boxes, denying access to TBP. Current interest focuses on the mechanisms by which this architecture is remodeled during embryogenesis. The transcription factor PvALF is intrinsically involved, as are other non-histone proteins and abscisic acid. These concepts, and the possible modular nature of phas expression, are summarized together with speculations concerning the re-establishment of the nucleosome over the phas promoter during terminal stages of embryogenesis.
Assuntos
Cromatina/química , Regulação da Expressão Gênica de Plantas , Proteínas de Plantas/genética , Plantas/genéticaRESUMO
The promoter for the phaseolin (phas) bean seed protein gene adopts an inactive chromatin structure in leaves of transgenic tobacco. This repressive architecture, which confers stringent spatial regulation, is disrupted upon transcriptional activation during embryogenesis in a process that requires the presence of both a transcription factor (PvALF) and abscisic acid (ABA). Toward determining the need for de novo synthesis of proteins other than PvALF in transcriptional activation we explored the effect of several eukaryotic protein synthesis inhibitors. Surprisingly, cycloheximide (CHX), emetine, and verrucarin A were able to induce transcription from the phas promoter in tobacco and bean leaf tissue in the absence of either PvALF or ABA. This induction was decreased by the replication inhibitors hydroxyurea and aphidicolin but not by genistein or mimosine. Since protein phosphatases and kinases are essential components of the ABA signal transduction pathway, it is conceivable that CHX is also capable of inducing phosphorylation of proteins usually involved in ABA-mediated activation. Interestingly, okadaic acid, an inhibitor of serine/threonine phosphatase, also strongly activated transcription from the phas promoter. In contrast, the protein synthesis inhibitors anisomycin and puromycin did not activate transcription from the phas promoter, nor did the tyrosine phosphatase inhibitors phenylarsine oxide and sodium orthovanadate. These discrete but different results on transcriptional activation may reflect specific modes of action of the inhibitors, or they may reflect differential interactions of the inhibitors or of downstream events resulting from inhibitor activity with presently unknown components of the transcriptional activation system.
Assuntos
Cicloeximida/farmacologia , Fabaceae/genética , Fosfoproteínas Fosfatases/metabolismo , Proteínas de Plantas/genética , Plantas Medicinais , Regiões Promotoras Genéticas , Inibidores da Síntese de Proteínas/farmacologia , Replicação do DNA , Inibidores Enzimáticos/farmacologia , Ácido Okadáico/farmacologia , Fosfoproteínas Fosfatases/antagonistas & inibidores , Ativação TranscricionalRESUMO
Plant gene silencing was originally thought to be a quirk of transformation procedures, but is now recognized to be a facet of vitally important gene regulatory systems, present in all organisms. Monocot plants, especially the grasses, play a foremost role in the agricultural economy of all nations, and their biotechnological manipulation offers great potential for both developed and developing countries. Here, we review reported instances of transgene silencing in monocots and relate the processes of transcriptional and post-transcriptional gene silencing (TGS, PTGS) in perspective to the rapidly burgeoning knowledge of these phenomena in many organisms. Recent findings include the involvement of an RNA-dependent RNA polymerase and a nuclease in PTGS systems and the close relationship between methylation and chromatin structure in TGS events.
Assuntos
Grão Comestível/genética , Inativação Gênica , Transgenes/genética , Regulação da Expressão Gênica de Plantas , Plantas Geneticamente ModificadasRESUMO
Nicotiana benthamiana plants expressing Brome mosaic virus (BMV) p2 protein complemented replication of RNAs1 + 3 but, surprisingly, supported little or no replication of RNA-2. Despite this, the p2 transgenic plants were able to support systemic migration of RNAs-1 and -3. Kinetic analyses showed identical degradation rates for RNAs-2 and -3, greatly detracting from the concept of an induction of an RNA-2-specific degradation system. Deletion analysis identified a 200-nucleotide sequence that may contribute to silencing in a context-specific manner. When R1 progeny of a severely silencing p2 transgenic line were tested for virus resistance, three different classes of reactions were observed. In class 1 and class 3 plants, the virus moved systemically and showed various extents of RNA-2 silencing. However, in class 2 plants, there was a stochastic onset of post-transcriptional silencing in the systemic leaves that was reminiscent of virus recovery. Plants showing recovery tended to have a greater number of transgene loci than did those exhibiting component-specific silencing. The induction of silencing did not appear to be dependent solely on the combined steady state levels of the transgene and viral RNA. Some plants transformed with a p2 frameshift construct showed a complete silencing phenotype, but none showed RNA-2-specific silencing. While the relationship between the two types of silencing remains unclear, we speculate that our observations reflect early events in the induction of virus recovery.