Incidence of Respiratory Syncytial Virus-Associated Lower Respiratory Tract Illness in Infants in Low- and Middle-Income Regions During the Coronavirus Disease 2019 Pandemic

Background

Incidence data of respiratory syncytial virus-associated lower respiratory tract illness (RSV-LRTI) are sparse in low- and middle-income countries (LMICs). We estimated RSV-LRTI incidence rates (IRs) in infants in LMICs using World Health Organization case definitions.

Methods

This prospective cohort study, conducted in 10 LMICs from May 2019 to October 2021 (largely overlapping with the coronavirus disease 2019 [COVID-19] pandemic), followed infants born to women with low-risk pregnancies for 1 year from birth using active and passive surveillance to detect potential LRTIs, and quantitative reverse-transcription polymerase chain reaction on nasal swabs to detect RSV.

Results

Among 2094 infants, 32 (1.5%) experienced an RSV-LRTI (8 during their first 6 months of life, 24 thereafter). Seventeen (0.8%) infants had severe RSV-LRTI and 168 (8.0%) had all-cause LRTI. IRs (95% confidence intervals [CIs]) of first RSV-LRTI episode were 1.0 (.3-2.3), 0.8 (.3-1.5), and 1.6 (1.1-2.2) per 100 person-years for infants aged 0-2, 0-5, and 0-11 months, respectively. IRs (95% CIs) of the first all-cause LRTI episode were 10.7 (8.1-14.0), 11.7 (9.6-14.0), and 8.7 (7.5-10.2) per 100 person-years, respectively. IRs varied by country (RSV-LRTI: 0.0-8.3, all-cause LRTI: 0.0-49.6 per 100 person-years for 0- to 11-month-olds).

Conclusions

RSV-LRTI IRs in infants in this study were relatively low, likely due to reduced viral circulation caused by COVID-19-related nonpharmaceutical interventions.

Clinical Trials Registration

NCT03614676.

Clinical leadership and coping strategies in times of COVID-19: observational study with health managers in Mendoza

BACKGROUND

The outbreak of the COVID-19 pandemic required an immediate response to the healthcare challenges it posed. This study was conducted to identify actions that helped healthcare professionals to overcome the initial impact in Mendoza (Argentina).

METHODS

A cross-sectional study was carried out in a non-random sample of managers and staff of the public health system of Mendoza (Argentina) (n = 134). An ad-hoc and voluntary survey was carried out with 5 multi-response questions that combined questions referring to the management of the pandemic at the organizational level with others referring to coping at the individual level. The survey questions were formulated based on the results of six focus groups that were conducted previously. Descriptive frequency analysis was performed.

RESULTS

60 people agreed to participate and 45 answered the full questionnaire. At both the organizational and individual level, there was consensus with at least 50% of votes. The most outstanding at the organizational level was "Prioritize the need according to risk" and at the individual level it was "Support from family or friends", being also the most voted option in the whole questionnaire.

CONCLUSIONS

The responses that emerged for coping with COVID-19 must be seen as an opportunity to identify strategies that could be effective in addressing future crisis situations that jeopardize the system's response capacity. Moreover, it is essential to retain both changes at the organizational level (e.g., new protocols, multidisciplinary work, shift restructuring, etc.) and coping strategies at the individual level (e.g., social support, leisure activities, etc.) that have proven positive outcomes.

Comparison of Epidemiologic and Clinical COVID-19 Profiles in Children in Argentina, During Circulation of Original and Variant (Alpha, Gamma and Lambda) Strains

BACKGROUND

Information on the impact of the different variants in children in Latin America is scarce. The objective of this study was to describe epidemiologic and clinical features of COVID-19 infection in children under 18 years of age in Argentina, comparing the periods before and after the circulation of new variants.

METHODS

Observational, cross-sectional, multicentric, analytical study. All patients under 18 years of age with confirmed SARS-CoV-2 infection admitted at 22 healthcare centers were included. Two study periods were established: Period 1 (EW10-2020 to EW12-2021) for the Wuhan strain; Period 2 (EW13 to EW35 2021) for Alpha, Gamma, Delta and Lambda variants.

FINDINGS

A total of 6330 confirmed cases were included. Period 1: 3575 (56.5%), period 2: 2755 (43.5%). During period 2, a lower number of asymptomatic cases was observed, while general, respiratory and neurologic signs and symptoms increased in all age groups. Oxygen therapy requirement was higher during the first period (36.7% vs 19.1%; P < 0.001). No significant differences were observed in the rates of severe or critical cases (6.3% vs 5,4%; P = 0.102), intensive care admission (2.1% vs 2%; P < 0.656) or case fatality (0.3% vs 0.5 %; P < 0.229). MIS-C cases occurred more frequently during the first period (1.9% vs 1.1%; P = 0.009).

INTERPRETATION

The clinical spectrum of COVID-19 in Argentina has evolved. With the emergence of new variants, although the number of asymptomatic cases declined, numbers of severe and critical cases, as well as case fatality rates in children, remained unchanged.

2128. Lack of Congenital Transmission in Infants Born of Female Patients with Chagas Disease who Became Pregnant During a Nifurtimox Study (CHICO and CHICO SECURE Study)

Background

There is some concern about the safety of nifurtimox (NF) for the offspring of treated women. Potential genotoxicity of NF was reported in in vitro models. However, the evidence to support the risks in fetal development is lacking for humans. In addition, a preventative effect over transplacental transmission was reported in girls and women with T.cruzi infection treated before pregnancy (mainly with benznidazole).

Methods

A multicenter, randomized, double-blind phase 3 clinical trial (NCT02625974) was set up to evaluate safety and efficacy of NF. A total of 330 patients, younger 18 years old, were enrolled, 67 were females of child-bearing age.

The enrolled females of childbearing age agreed to use an effective method of contraception until 3 months after the last administration of NF. Pregnancy tests were performed at screening, during treatment and 30 days after end of treatment.

Results

No pregnancies were reported during treatment period. There were 5 pregnancies reported during the 1^st year of post-treatment follow-up and another 21 pregnancies during the additional 3-year follow-up period. Two mothers did not consent to have their babies tested for T cruzi infection, and in one case an abortion was reported. Two women gave birth twice. There was information about transplacental transmission available in 18 babies. All mothers were T.cruzi RT-PCR negative at the end of the treatment period and remained negative during follow up.

All newborns were live, healthy full-term and of weight appropriate for their gestational age, and had no perinatal complications except one baby who was healthy but small for gestational age. T.cruzi infection was ruled out by a negative direct parasitological test during the first days of life in 12 infants , and /or by ELISA T.cruzi serology at 8 -12 months of age in 14 infants, which was negative in all cases.

Conclusion

Our results showed that treatment of females on childbearing age with nifurtimox may prevent transplacental transmission of CD as was reported previously for benznidazole.

Disclosures

Jaime ALTCHEH, Sr., MD,PhD, Bayer: Advisor/Consultant.

Cost-Effective Method to Perform SARS-CoV-2 Variant Surveillance: Detection of Alpha, Gamma, Lambda, Delta, Epsilon, and Zeta in Argentina

SARS-CoV-2 variants with concerning characteristics have emerged since the end of 2020. Surveillance of SARS-CoV-2 variants was performed on a total of 4,851 samples from the capital city and 10 provinces of Argentina, during 51 epidemiological weeks (EWs) that covered the end of the first wave and the ongoing second wave of the COVID-19 pandemic in the country (EW 44/2020 to EW 41/2021). The surveillance strategy was mainly based on Sanger sequencing of a Spike coding region that allows the identification of signature mutations associated with variants. In addition, whole-genome sequences were obtained from 637 samples. The main variants found were Gamma and Lambda, and to a lesser extent, Alpha, Zeta, and Epsilon, and more recently, Delta. Whereas, Gamma dominated in different regions of the country, both Gamma and Lambda prevailed in the most populated area, the metropolitan region of Buenos Aires. The lineages that circulated on the first wave were replaced by emergent variants in a term of a few weeks. At the end of the ongoing second wave, Delta began to be detected, replacing Gamma and Lambda. This scenario is consistent with the Latin American variant landscape, so far characterized by a concurrent increase in Delta circulation and a stabilization in the number of cases. The cost-effective surveillance protocol presented here allowed for a rapid response in a resource-limited setting, added information on the expansion of Lambda in South America, and contributed to the implementation of public health measures to control the disease spread in Argentina.

Nineteen-years of pneumococcal invasive disease surveillance in a children's hospital in Mendoza, Argentina

Five hundred and thirty-seven children admitted to Hospital Dr. Notti and diagnosed with invasive pneumococcal disease between 1993 and 2011 were studied. Their median age was 19 months (range= 0-192 months); 34.82% were <1 year old and 23.46%, >60 months old. Pneumonia with or without effusion (48.04%) and meningitis (29.05%) were the most predominant conditions, with a case fatality rate of 6.14%. Identified serotypes corresponded to 14, 5 and 1 in56.86% of cases. Sensitivity to penicillin was observed in99.74% of non-meningeal strains, while sensitivity to ceftriaxone was found in 98.08% ofmeningeal strains. Risk factors inpneumonia with effusionwere associated to age >60 months old, RR: 1.47 (1.06-2.04), p= 0.02, to serotype 5, RR: 2.57 (1.71-3.87), p= 0.0001, and to serotype 1, RR: 1.86 (1.17-2.96), p= 0.014; in the case of meningitis, risk factors were mainly associated to age <1 year old, RR: 2.35 (1.87-3.06), p= 0.0000, and to serotype 18C, RR: 2.19 (1.3-3.7), p= 0.024. Conclusion. Streptococcus pneumonia was a major problem in infants younger than one year old, who predominantly developed meningitis which caused half of deaths, and in children older than 60 months old, who had a prevalence of pneumonia with effusion. Most cases were sensitive to penicillin and ceftriaxone.

Efficacy of pneumococcal nontypable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in young Latin American children: A double-blind randomized controlled trial

BACKGROUND

The relationship between pneumococcal conjugate vaccine-induced antibody responses and protection against community-acquired pneumonia (CAP) and acute otitis media (AOM) is unclear. This study assessed the impact of the ten-valent pneumococcal nontypable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) on these end points. The primary objective was to demonstrate vaccine efficacy (VE) in a per-protocol analysis against likely bacterial CAP (B-CAP: radiologically confirmed CAP with alveolar consolidation/pleural effusion on chest X-ray, or non-alveolar infiltrates and C-reactive protein ≥ 40 µg/ml); other protocol-specified outcomes were also assessed.

METHODS AND FINDINGS

This phase III double-blind randomized controlled study was conducted between 28 June 2007 and 28 July 2011 in Argentine, Panamanian, and Colombian populations with good access to health care. Approximately 24,000 infants received PHiD-CV or hepatitis control vaccine (hepatitis B for primary vaccination, hepatitis A at booster) at 2, 4, 6, and 15-18 mo of age. Interim analysis of the primary end point was planned when 535 first B-CAP episodes, occurring ≥2 wk after dose 3, were identified in the per-protocol cohort. After a mean follow-up of 23 mo (PHiD-CV, n = 10,295; control, n = 10,201), per-protocol VE was 22.0% (95% CI: 7.7, 34.2; one-sided p = 0.002) against B-CAP (conclusive for primary objective) and 25.7% (95% CI: 8.4%, 39.6%) against World Health Organization-defined consolidated CAP. Intent-to-treat VE was 18.2% (95% CI: 5.5%, 29.1%) against B-CAP and 23.4% (95% CI: 8.8%, 35.7%) against consolidated CAP. End-of-study per-protocol analyses were performed after a mean follow-up of 28-30 mo for CAP and invasive pneumococcal disease (IPD) (PHiD-CV, n = 10,211; control, n = 10,140) and AOM (n = 3,010 and 2,979, respectively). Per-protocol VE was 16.1% (95% CI: -1.1%, 30.4%; one-sided p = 0.032) against clinically confirmed AOM, 67.1% (95% CI: 17.0%, 86.9%) against vaccine serotype clinically confirmed AOM, 100% (95% CI: 74.3%, 100%) against vaccine serotype IPD, and 65.0% (95% CI: 11.1%, 86.2%) against any IPD. Results were consistent between intent-to-treat and per-protocol analyses. Serious adverse events were reported for 21.5% (95% CI: 20.7%, 22.2%) and 22.6% (95% CI: 21.9%, 23.4%) of PHiD-CV and control recipients, respectively. There were 19 deaths (n = 11,798; 0.16%) in the PHiD-CV group and 26 deaths (n = 11,799; 0.22%) in the control group. A significant study limitation was the lower than expected number of captured AOM cases.

CONCLUSIONS

Efficacy was demonstrated against a broad range of pneumococcal diseases commonly encountered in young children in clinical practice.

TRIAL REGISTRATION

www.ClinicalTrials.gov NCT00466947.

[Skin and soft tissue infections in children: consensus on diagnosis and treatment]

Skin and soft tissue infections are a common reason for consultation in primary health care centers. Data from the local epidemiology of these infections are rare, but Staphylococcus aureus and Streptococcus pyogenes are known to be the major etiologic agents. The appearance in recent years of community-originated strains of methicillin-resistant S. aureus and erythromycin-resistant pyogenes raises controversy in the choice of initial empirical treatment. This national consensus is for pediatricians, dermatologists, infectologists and other health professionals. It is about clinical management, especially the diagnosis and treatment of community-originated skin and soft tissue infections in immunocompetent patients under the age of 19.

[Study of respiratory influenza A H1N1 Virus (pH1N1) in hospitalized children in the pandemic year. Experience in 34 centers in Argentina]

INTRODUCTION

In Argentina, pandemic influenza pH1N1 caused nearly 10,000 confirmed cases with high impact in pediatrics.

OBJECTIVES

To describe clinical and epidemiological characteristics and analyse the risk factor of lethality in children hospitalized with infection pH1N1 confirmed by PCR.

POPULATION AND METHODS

We identifed all suspected cases (according to Ministry of health) in 34 centers and we included all the confirmed cases of 0-18 years from 1/4/09 to 31/8/09 in a retrospective cohort study. The viral diagnosis was confirmed by RT-PCR method. Data are expressed in percentages, average, median, standard deviation, and range (IQR) as appropriate; and as a measure of association, relative risk (RR), with 95% confidence interval (95%CI). Multiple logistic regression was conducted to determine the independent risk predictors.

RESULTS

Total number of suspected cases were: 2367; PCR was performed to 47.8% (n: 1131) being positive for pH1N1 65.5% (n: 741/1131); 57.2% males; 61.5% <24 months, median age: 14 months (IQR 6-46 months); 45.1% with underlying disease; more frequent clinical pictures were: pneumonia (39,7%) and bronchiolitis 25.8%; Case-fatality rate: 5.9% (44/741). Mortality risk factors were [RR (95%CI)]: neurological disease [5.00 (2.84-8.81)], genetic disease [3.67 (1.58-8.52)], malnutrition [3,07 (1.46-6.48)] and prematurity [2.28 (1.14-4.56)]. Independent mortality predictor: neurological disease [3.84 (1.81-8.14)]. No significant association between age, chronic respiratory disease, immunosuppression and viral co-infection with lethality was observed.

CONCLUSIONS

Almost half of children with pH1N1 infection had underlying disease; the neurological condition was a separate CFR predictor.

Identification of human DNA helicase V with the far upstream element-binding protein

The properties of human DNA helicase V (HDH V) were studied in greater detail following an improved purification procedure. From 450 g of cultured cells, <0.1 mg of pure protein was isolated. HDH V unwinds DNA unidirectionally by moving in the 3' to 5' direction along the bound strand in an ATP- and Mg(2+)-dependent fashion. The enzyme is not processive and can also unwind partial RNA-RNA duplexes such as HDH IV and HDH VIII. The M:(r) determined by SDS-PAGE (66 kDa) corresponds to that measured under native conditions, suggesting that HDH V exists as a monomer in the nucleus. Microsequencing of the purified HDH V shows that this enzyme is identical to the far upstream element-binding protein (FBP), a protein that stimulates the activity of the c-myc gene by binding specifically to the 'FUSE' DNA region localized upstream of its promoter. The sequence of HDH V/FBP contains RGG motifs like HDH IV/nucleolin, HDH VIII/G3BP as well as other human RNA and DNA helicases identified by other laboratories.

Selection of homeotic proteins for binding to a human DNA replication origin

We have previously shown that a cell cycle-dependent nucleoprotein complex assembles in vivo on a 74 bp sequence within the human DNA replication origin associated to the Lamin B2 gene. Here, we report the identification, using a one-hybrid screen in yeast, of three proteins interacting with the 74 bp sequence. All of them, namely HOXA13, HOXC10 and HOXC13, are orthologues of the Abdominal-B gene of Drosophila melanogaster and are members of the homeogene family of developmental regulators. We describe the complete open reading frame sequence of HOXC10 and HOXC13 along with the structure of the HoxC13 gene. The specificity of binding of these two proteins to the Lamin B2 origin is confirmed by both band-shift and in vitro footprinting assays. In addition, the ability of HOXC10 and HOXC13 to increase the activity of a promoter containing the 74 bp sequence, as assayed by CAT-assay experiments, demonstrates a direct interaction of these homeoproteins with the origin sequence in mammalian cells. We also show that HOXC10 expression is cell-type-dependent and positively correlates with cell proliferation.

Start sites of bidirectional DNA synthesis at the human lamin B2 origin

The initiation sites of bidirectional synthesis at the DNA replication origin located at the 3' end of the human lamin B2 gene were investigated. RNA-primed nascent DNA molecules were subjected to second-strand synthesis with appropriate primers, amplified by ligation-mediated polymerase chain reaction, and size fractionated. Evidence for precise start sites was obtained. Exploration of close to 1 kilobase, coupled to inhibition of Okazaki fragment synthesis, demonstrates that the leading strands initiate at precise nucleotides on either helix, overlapping by three base pairs, within the area bound to a protein complex possibly analogous to the prereplicative complex of yeast.

Eukaryotic DNA replication: a model for a fixed double replisome

To duplicate their genomes, eukaryotic cells have to overcome some formidable chemical and topological hurdles, considering the number of nucleotides that have to be polymerized faithfully and the sheer physical size of the DNA molecules that have to be disentangled and partitioned in an orderly way. This article tackles one particular aspect of the process: the organization of the apparatus that advances the replicative growing forks along the DNA molecule. Here, I suggest a solution to the difficulty of separating the daughter molecules in an orderly way and propose an alternative to the current models, which reconciles the use of a single polarity of synthesis by the DNA polymerases with the need for parallel polymerization of two strands of opposite polarity.

Replication origins of mammalian chromosomes: the happy few

Replication of eukaryotic cell genomes is a tightly controlled process occurring once and only once per cell cycle. Replication initiates at several thousand origins, whose cis-acting sequences and trans-acting proteins have been partially characterized in the yeast S. cerevisiae in the last few years. In contrast, identification of origins of DNA replication in mammalian cells have proven much more difficult. Currently, less then 20 bona fide mammalian origins have been identified, of which only few characterized in detail. Here we discuss the available methods for origin identification in mammalian DNA and the main results, sometimes controversial, so far generated by their application. In particular, we review the currently available information concerning the three best characterized origins, namely those in the lamin B2 and b-globin gene domains in human cells and the one located downstream of the dihydrofolate reductase gene in hamster cells.

Familial dilated cardiomyopathy: evidence for genetic and phenotypic heterogeneity. Heart Muscle Disease Study Group

OBJECTIVES

This study was performed to evaluate the characteristics, mode of inheritance and etiology of familial dilated cardiomyopathy (FDC).

BACKGROUND

A genetic form of disease transmission has been identified in a relevant proportion of patients with dilated cardiomyopathy (DCM). Variable clinical characteristics and patterns of inheritance, and an increased frequency of cardiac antibodies have been reported. An analysis of FDC may improve the understanding of the disease and the management of patients.

METHODS

Of 350 consecutive patients with idiopathic DCM, 281 relatives from 60 families were examined. Family studies included clinical examination, electrocardiography, echocardiography and blood sampling. Of the 60 DCM index patients examined, 39 were attributable to FDC and 21 were due to sporadic DCM. Clinical features, histology, mode of inheritance and autoimmune serology were examined, molecular genetic studies were undertaken and the difference between familial and sporadic forms was analyzed.

RESULTS

Only a younger age (p = 0.0005) and a higher ejection fraction (p = 0.03) could clinically distinguish FDC patients from those with sporadic DCM. However, a number of distinct subtypes of FDC were identified: 1) autosomal dominant, the most frequent form (56%); 2) autosomal recessive (16%), characterized by worse prognosis; 3) X-linked FDC (10%), with different mutations of the dystrophin gene; 4) a novel form of autosomal dominant DCM with subclinical skeletal muscle disease (7.7%); 5) FDC with conduction defects (2.6%), and 6) rare unclassifiable forms (7.7%). The forms with skeletal muscle involvement were characterized by a restrictive filling pattern; the forms with isolated cardiomyopathy had an increased frequency of organ-specific cardiac autoantibodies. Histologic signs of myocarditis were frequent and nonspecific.

CONCLUSIONS

Familial dilated cardiomyopathy is frequent, cannot be predicted on a clinical or morphologic basis and requires family screening for identification. The phenotypic heterogeneity, different patterns of transmission, different frequencies of cardiac autoantibodies and the initial molecular genetic data indicate that multiple genes and pathogenetic mechanisms can lead to FDC.

Gene therapy of chronic granulomatous disease (CGD) by gene transfer into hematopoietic stem cells

Chronic granulomatous disease (CGD) is an inherited immunodeficiency characterized by severe recurrent bacterial and fungal infections of several organs. The disease is due to the inability of phagocytic leukocytes to generate reactive oxygen species upon phagocytosis. The defect arises as a consequence of mutations of the genes encoding for the subunits of a membrane NADPH oxidase, which catalyzes the production of superoxide anion (O2-). CGD represents an ideal candidate disorder for gene therapy, since the disease has a recessive inheritance, its phenotype is exclusively expressed in phagocytic cells, and a partial correction is likely to be effective. Given the short half-life of mature phagocytes, the optimal target cell population for gene transfer is the pluripotent hematopoietic stem cell. Transduction of CD34+ hematopoietic progenitors with retroviral vectors carrying the cDNA of the defective gene results in the correction of the enzymatic defect in myeloid cells differentiated in vitro. Still, the effective development of a clinical gene therapy protocol for this disease will await a substantial improvement in our current technology for the identification and manipulation of hematopoietic stem cells, and in our understanding of their biological and molecular properties.

Human DNA helicase VIII: a DNA and RNA helicase corresponding to the G3BP protein, an element of the ras transduction pathway

Human DNA helicase VIII (HDH VIII) was isolated in the course of a systematic study of the DNA unwinding enzymes present in human cells. From a HeLa cell nuclear extract a protein with an Mrof 68 kDa in SDS-PAGE was isolated, characterised and micro-sequenced. The enzyme shows ATP- and Mg2+-dependent activity is not stimulated by RPA, prefers partially unwound 3'-tailed substrates and moves along the bound strand in the 5' to 3' direction. HDH VIII can also unwind partial RNA/DNA and RNA/RNA duplexes. Microsequencing of the polypeptide showed that this enzyme corresponds to G3BP, an element of the Ras pathway which binds specifically to the GTPase-activating protein. HDH VIII/G3BP is analogous to the heterogeneous nuclear ribonucleoproteins and contains a sequence rich in RGG boxes similar to the C-terminal domain of HDH IV/nucleolin, another DNA and RNA helicase.

Cell cycle modulation of protein-DNA interactions at a human replication origin

We followed the variations of protein-DNA interactions occurring in vivo over the early firing replication origin located near the human lamin B2 gene, in IMR-90 cells synchronized in different moments of the cell cycle. In G0 phase cells no protection is present; as the cells progress in G1 phase an extended footprint covering over 100 bp appears, particularly marked at the G1/S border. As the cells enter S phase the protection shrinks to 70 bp and remains unchanged throughout this phase. In mitosis the protection totally disappears, only to reappear in its extended form as the cells move into the next G1. These variations are reminiscent of those corresponding to the formation of the pre- and post-replicative complexes described in yeast and Xenopus cells.

DNA loop anchorage region colocalizes with the replication origin located downstream to the human gene encoding lamin B2

The recently developed procedure of topoisomerase II-mediated DNA loop excision has been used to analyze the topological organization of a human genome fragment containing the gene encoding lamin B2 and the ppv1 gene. A 3.5 kb long DNA loop anchorage/topoisomerase II cleavage region was found within the area under study. This region includes the end of the lamin B2 coding unit and an intergenic region where an origin of DNA replication was previously found. These observations further corroborate the hypothesis that DNA replication origins are located at or close to DNA loop anchorage regions.

A somatostatin analogue induces translocation of Ku 86 autoantigen from the cytosol to the nucleus in colon tumour cells

Flow cytometric and electron microscopic immunocytochemical studies have been performed in HT-29 human colon tumour cells in vitro, to determine and localise p86 Ku protein, which is a regulatory subunit of DNA-dependent kinase and a specific binding site for somatostatin. We have demonstrated that HT-29 cells contain p86 Ku and that the distribution between the cytoplasm and the nucleus is even. After administration of the somatostatin analogues Sandostatin and TT-232 to HT-29 cells, the p86 Ku content of the cytoplasmic compartment decreased in the first 4 h. An increase in the content of this protein in the nuclear compartment was observed at hour 1 followed by a decrease at hour 4 after treatment. Quantitative differences between the two analogues have been observed in this respect. The practical significance of these findings is discussed.

Dystrophin gene abnormalities in two patients with idiopathic dilated cardiomyopathy

Two new cases of dilated cardiomyopathy (DC) caused by dystrophinopathy are reported. One patient, a 24 year old man, had a family history of X linked DC, while the other, a 52 year old man, had sporadic disease. Each had abnormal dystrophin immunostaining in muscle or cardiac biopsy specimens, but neither had muscle weakness. Serum creatine kinase activity was raised only in the patient with familial disease. Analysis of dystrophin gene mutations showed a deletion of exons 48-49 in the patient with familial DC and of exons 49-51 in the other. Dystrophin transcription in cardiac tissue from the patient with sporadic disease showed abundant expression, predominantly of the muscle isoform. This study, together with previous reports, suggests that some patients with DC have a dystrophinopathy that can be diagnosed using a combination of biochemical and genetic analyses.

Functional properties of the separate subunits of human DNA helicase II/Ku autoantigen

The Ku antigen consists of two subunits of 70 and 83 kDa and is endowed with both duplex DNA end-binding capacity and helicase activity (human DNA helicase II). HeLa Ku can be isolated from in vitro cultured human cells uniquely as a heterodimer, and the subunits can be separated by electrophoresis only under denaturing conditions. To dissect the molecular functions of the two subunits of the heterodimer, we have cloned and expressed their cDNAs separately in Escherichia coli. The two activities of Ku (DNA binding and unwinding) were reconstituted by mixing and refolding both subunits in equimolar amounts (Tuteja, N., Tuteja, R., Ochem, A., Taneja, P., Huang, N-W., Simoncsits, A., Susic, S., Rahman, K., Marusic, L., Chen, J., Zang, J., Wang, S., Pongor, S., and Falaschi, A. (1994) EMBO J. 13, 4991-5001). Renaturation of the separate subunits can be achieved in the presence of a synthetic solubilizing and stabilizing agent, dimethyl ethylammonium propane sulfonate (NDSB 195). The helicase activity of the Ku protein resides uniquely in the 70-kDa subunit, whereas the DNA end-binding activity can be reconstituted only through renaturation of the two subunits in the heterodimeric form and is practically absent in the separate subunits. The 83-kDa subunit, when refolded in the absence of the 70-kDa subunit, forms homodimers unable to unwind DNA and bind duplex ends. The three separate species (heterodimer, 70-kDa subunit, and 83-kDa subunit homodimer) all have ssDNA-dependent ATPase activity.

Mapping replication origins by quantifying relative abundance of nascent DNA strands using competitive polymerase chain reaction

A procedure was developed for mapping origins of DNA replication in mammalian cell chromosomes based on determining the relative abundance of nascent DNA strands throughout a specific genomic region. The method entails purification of short strands of nascent DNA derived from recently activated origins and the quantification, within this sample, of the relative abundances of different adjacent DNA segments by a competitive polymerase chain reaction technique. It is expected that the abundance of defined markers within the origin region is greatest at the site where DNA replication begins. This origin mapping procedure (i) allows analysis of single-copy genomic regions, (ii) can be performed on cultured and primary cells in the absence of any chemical treatment, (iii) does not require cell synchronization, and (iv) allows mapping origins to within a few hundred base pairs. This high degree of resolution permits a study of the cis- and trans-acting elements required for origin function. Application of this method to single-copy sequences in mammalian cells has identified replication origins within an approximately 500-bp segment in the human lamin B2 gene domain and within an approximately 800-bp segment in the hamster dihydrofolate reductase gene locus.

Inhibition of DNA unwinding and ATPase activities of human DNA helicase II by chemotherapeutic agents

DNA helicases catalyze the unwinding of duplex DNA and thus play important roles in the processing of DNA, little is known about the effects of various cytotoxic or antitumor chemotherapeutic agents on purified human DNA helicases. We have determined the effect of actinomycin C1, VP-16, camptothecin, ethidium bromide, ellipticine, nogalamycin, novobiocin, genistein, m-AMSA, aphidicolin and daunorubicin on the enzymatic activities of purified human DNA helicase II which was identified as Ku autoantigen. Ku contains DNA helicase, ATPase and DNA end binding activities. Our data have shown that out of several chemotherapeutic agents tested ethidium bromide, actinomycin C1, daunorubicin and nogalamycin were inhibitors of DNA unwinding activity of human DNA helicase II with ID50 values of 8.44 microM, 11.68 microM, 6.23 microM and 0.42 microM respectively. These inhibitors also inhibited the ATPase activity but not the DNA binding activity of this helicase. This inhibition could be due to binding of these drugs to DNA, thereby impeding the movement of the helicase for unwinding action which may be their most important pharmacological function against cancer cells.

High-resolution mapping of the origin of DNA replication in the hamster dihydrofolate reductase gene domain by competitive PCR

By the use of a highly sensitive mapping procedure allowing the identification of the start sites of DNA replication in single-copy genomic regions of untreated, exponentially growing cultured cells (M. Giacca, L. Zentilin, P. Norio, S. Diviacco, D. Dimitrova, G. Contreas, G. Biamonti, G. Perini, F. Weighardt, S. Riva, and A. Falaschi, Proc. Natl. Acad. Sci. USA 91:7119-7123, 1994), the pattern of DNA replication of the Chinese hamster dihydrofolate reductase (DHFR) gene domain was investigated. The method entails the purification of short stretches of nascent DNA issuing from DNA replication origin regions and quantification, within this sample, of the abundance of different adjacent segments by competitive PCR. Distribution of marker abundance peaks around the site from which newly synthesized DNA had emanated. The results obtained by analysis of the genomic region downstream of the DHFR single-copy gene in asynchronous cultures of hamster CHO K1 cells are consistent with the presence of a single start site for DNA replication, located approximately 17 kb downstream of the gene. This site is coincident with the one detected by other studies using different techniques in CHO cell lines containing an amplified DHFR gene domain.

Utilization of the same DNA replication origin by human cells of different derivation

In the past, a highly sensitive and efficient method was developed to map DNA replication origins in human cells, based on quantitative PCR performed on nascent DNA samples. This method allowed the identification of a replication origin in the myeloid HL-60 cell line, located on chromosome 19 within an approximately 500 bp segment near the lamin B2 gene [Giacca et al. (1994) Proc. Natl. Acad. Sci. USA, 91, 7119]. The same procedure has now been further simplified and extended to a variety of other exponentially growing human cells of different histological derivation (three neural, one connectival and one epithelial), with a nearly diploid chromosomal content. In all the six cell lines tested, the origin activity within the lamin B2 gene domain was localized to the same region. Furthermore, the lamin B2 origin was also found to be active in stimulated, but not in quiescent, peripheral blood lymphocytes.

Rapid retrovirus titration using competitive polymerase chain reaction

A quantitative polymerase chain reaction (PCR) procedure has been developed for rapid retrovirus titration. This procedure, which is based on the simultaneous amplification of the sample with known amounts of a competitor DNA fragment (competitive PCR), was used for the quantification of viral RNA genomes in retrovirus-producing cell clone supernatants and of proviral DNA molecules formed at 24 h after infection of different reference cell lines. The results obtained from the analysis of several samples indicated that proviral DNA quantification is in complete agreement with the number of selectable colonies in a standard colony assay. Conversely, the number of viral RNA genomes in the producer cell clone supernatants is a poor predictor of the actual efficiency of infection. Repeated competitive PCR experiments for provirus copy number determination at different times after transduction indicated that the number of proviral DNA molecules remains stable over time, suggesting stable integration into the host genome. The developed procedure is rapid and simple, is applicable to retroviral constructs not containing a selectable gene and can be used to directly measure the efficiency of infection of any target cell type, thus overcoming the problem of the dependency of retroviral titer determination on the rate of expression of a selectable gene and on the efficiency of colony formation of a reference cell line.

Genetic factors in dilated cardiomyopathy

Recent studies have demonstrated that genetic factors are likely to play a major role in the pathogenesis of idiopathic dilated cardiomyopathy (IDC). In clinical surveys, a familial trait has been demonstrated in 20 to 30% of idiopathic dilated cardiomyopathy patients (familial dilated cardiomyopathy). Molecular genetic studies have confirmed the clinical hypothesis of genetic heterogeneity in familial dilated cardiomyopathy, and are currently producing relevant advances in the understanding of this disease. The autosomal dominant form is considered to be the most frequent form of inherited idiopathic dilated cardiomyopathy. After the exclusion of a large series of candidate genes, the first familial dilated cardiomyopathy gene has been mapped to the long arm of chromosome 9. A second locus has been found on chromosome 1. Moreover, in two large families, characterized by a peculiar form of conduction delays and later development of myocardial dysfunction, the disease loci have been mapped to chromosome 1 and 3, respectively. The identification of the disease genes is in progress. In families with X-linked dilated cardiomyopathy, the disease gene has been identified as the dystrophin gene. The 5' end of the gene appears to be the critical region for the development of dilated cardiomyopathy without clinical evidence of muscle dystrophy. Furthermore, other cytoskeletal proteins, such as adhalin, could be involved in the pathogenesis of familial dilated cardiomyopathy. In familial right ventricular cardiomyopathy (or arrhythmogenic right ventricular dysplasia) characterized by isolated or prevalent right ventricular involvement, three different disease loci have been identified so far: two localized on the long arm of chromosome 14 and one on chromosome 1. The disease genes are still unknown and are currently under investigation. The study of the genetic factors at the molecular level is starting to elucidate the pathogenetic mechanisms of idiopathic dilated cardiomyopathy. These findings will also have relevant clinical and therapeutic implications.

Activation of transcription factor NF-kappaB by the Tat protein of human immunodeficiency virus type 1

A recombinant Tat protein was used to investigate the molecular mechanisms of transcriptional activation of the human immunodeficiency virus type 1 long terminal repeat (LTR). Liposome-mediated delivery of this protein to responsive cells results in dose-dependent LTR activation. As evaluated by mRNA quantitation with competitive PCR, the activation response is rapid and transient, peaking at 5 h after the beginning of Tat treatment. In vivo footprinting experiments at the LTR showed that transcriptional activation is concomitant with a modification of the protein-DNA interaction pattern at the downstream kappaB site of the enhancer and at the adjacent Sp1 boxes. The effects of Tat on the enhancer are mediated by Tat-induced nuclear translocation of NF-kappaB, which parallels the kinetics of transcriptional activation. This induction results from degradation of the inhibitor IkappaB-alpha, is blocked under antioxidant conditions and by a protease inhibitor, and occurs as a rapid response in different cell types. The functional response to Tat is impaired upon cell treatment with a kappaB site decoy or with sodium salicylate, an inhibitor of NF-kappaB activation. These results show that NF-kappaB activation by Tat is important for LTR transcriptional activation. Furthermore, they suggest that some of the pleiotropic effects of Tat on cellular functions can be mediated by induction of NF-kappaB.

Functional reconstitution of oxidase activity in X-linked chronic granulomatous disease by retrovirus-mediated gene transfer

The feasibility of correction of the disease phenotype by gene gene transfer was investigated in cells of four patients with X-linked chronic granulomatous disease. These patients carry point mutations of the gp91-phox gene, encoding for the large subunit of the catalytic core of the phagocytic cell NADPH oxidase. A retroviral vector expressing the gp91-phox protein was constructed and used to transduce lymphoblastoid cell lines established from the patients. Several transduced lymphoblastoid cell clones were investigated for mRNA and protein expression, and for functional reconstitution of oxidase activity. Although extensive quantitative variability was detected among different clones, functional reconstitution of O2- production was obtained in most cases, with oxidase function within the same range as in B cell lines derived from normal individuals. The same vector was also used for transduction of hematopoietic precursors from bone marrow or peripheral blood either with or without enrichment for CD34+ cells. A comprehensive analysis was performed on differentiated myeloid colonies, to evaluate the efficiency of transduction, the levels of gp91-phox expression, and the extent of functional reconstitution of oxidase activity. A high efficiency of transduction was obtained in most experiments, with 60-100% of colonies containing proviral DNA. Among the transduced colonies, an extensive variability in the levels of expression of the transduced gene and of functional restoration of NADPH oxidase activity was observed. These results represent a step toward the development of a gene therapy protocol for these patients.

In vivo protein-DNA interactions at human DNA replication origin

Protein-DNA interactions were studied in vivo at the region containing a human DNA replication origin, located at the 3' end of the lamin B2 gene and partially overlapping the promoter of another gene, located downstream. DNase I treatment of nuclei isolated from both exponentially growing and nonproliferating HL-60 cells showed that this region has an altered, highly accessible, chromatin structure. High-resolution analysis of protein-DNA interactions in a 600-bp area encompassing the origin was carried out by the in vivo footprinting technique based on the ligation-mediated polymerase chain reaction. In growing HL-60 cells, footprints at sequences homologous to binding sites for known transcription factors (members of the basic-helix-loop-helix family, nuclear respiratory factor 1, transcription factor Sp1, and upstream binding factor) were detected in the region corresponding to the promoter of the downstream gene. Upon conversion of cells to a nonproliferative state, a reduction in the intensity of these footprints was observed that paralleled the diminished transcriptional activity of the genomic area. In addition to these protections, in close correspondence to the replication initiation site, a prominent footprint was detected that extended over 70 nucleotides on one strand only. This footprint was absent from nonproliferating HL-60 cells, indicating that this specific protein-DNA interaction might be involved in the process of origin activation.

A new locus for arrhythmogenic right ventricular dysplasia on the long arm of chromosome 14

Familial arrhythmogenic right ventricular cardiomyopathy or dysplasia (ARVD) is an idiopathic heart muscle disease with an autosomal-dominant pattern of transmission, characterized by fibro-fatty replacement of the right ventricular myocardium and ventricular arrhythmias. Recently, linkage to the chromosome 14q23-q24 (locus D14S42) has been reported in two families. In the present study, three unrelated families with ARVD were investigated. According to strict diagnostic criteria, 13 of 37 members were considered to be affected. Linkage to the D14S42 locus was excluded. On the other hand, linkage was found in the region 14q12-q22 in all three families (cumulative two-point lod score is 3.26 for D14S252), with no recombination between the detected locus and the disease gene. With multipoint linkage analysis, a maximal cumulative lod score of 4.7 was obtained in the region between loci D14S252 and D14S257. These data indicate that a novel gene causing familial ARVD (provisionally named ARVD2) maps to the long arm of chromosome 14, thus supporting the hypothesis of genetic heterogeneity in this disease.

A point mutation in the 5' splice site of the dystrophin gene first intron responsible for X-linked dilated cardiomyopathy

X-linked dilated cardiomyopathy (XLDC) is a familial heart disease presenting in young males as a rapidly progressive congestive heart failure, without clinical signs of skeletal myopathy. This condition has recently been linked to the dystrophin gene in some families and deletions encompassing the genomic region coding for the first muscle exon have been detected. In order to identify the defect responsible for this disease at the molecular level and to understand the reasons for the selective heart involvement, a family with a severe form of XLDC was studied. In the affected members, no deletions of the dystrophin gene were observed. Analysis of the muscle promoter, first exon and intron regions revealed the presence of a single point mutation at the first exon-intron boundary, inactivating the universally conserved 5' splice site consensus sequence of the first intron. This mutation introduced a new restriction site for MseI, which cosegregates with the disease in the analyzed family. Expression of the major dystrophin mRNA isoforms (from the muscle-, brain- and Purkinje cell-promoters) was completely abolished in the myocardium, while the brain- and Purkinje cell- (but not the muscle-) isoforms were detectable in the skeletal muscle. Immunocytochemical studies with anti-dystrophin antibodies showed that the protein was reduced in quantity but normally distributed in the skeletal muscle, while it was undetectable in the cardiac muscle. These findings indicate that expression of the muscle dystrophin isoform is critical for myocardial function and suggest that selective heart involvement in dystrophin-linked dilated cardiomyopathy is related to the absence, in the heart, of a compensatory expression of dystrophin from alternative promoters.

Molecular genetics of dilated cardiomyopathies

The application of molecular genetics in cardiology is currently producing important results in the study of the pathogenetic mechanisms underlying cardiomyopathies. Recent clinical surveys have indicated that genetic factors play a major pathogenetic role in idiopathic dilated cardiomyopathy (IDC). Familial IDC is frequent (20-30%) and is probably a heterogeneous entity, as suggested by the clinical variability and the different pattern of inheritance in the affected families. Molecular genetic studies have demonstrated the existence of heterogeneity also at the genetic level. In a series of families with X-linked IDC, the disease gene has been identified as the dystrophin gene. In familial right ventricular cardiomyopathy (or right ventricular dysplasia), a new nosological entity characterized by isolated right ventricular involvement that can mimic IDC, the disease gene has been localized in the long arm of chromosome 14. In families with matrilineal transmission, the cardiomyopathy could be linked to mitochondrial DNA alterations. Autosomal dominant familial IDC, considered to be the most frequent form, is currently under active investigation. Our preliminary data have excluded a large series of candidate genes, among which are the cardiac beta-myosin heavy chain and several other genes encoding for cardiac contractile proteins, genes of the HLA region, and about 60 genes involved in the immune regulation.

Linkage of familial dilated cardiomyopathy to chromosome 9. Heart Muscle Disease Study Group

Idiopathic dilated cardiomyopathy is a heart muscle disease of unknown etiology, characterized by impaired myocardial contractility and ventricular dilatation. The disorder is an important cause of morbidity and mortality and represents the chief indication for heart transplantation. Familial transmission is often recognized (familial dilated cardiomyopathy, or FDC), mostly with autosomal dominant inheritance. In order to understand the molecular genetic basis of the disease, a large six-generation kindred with autosomal dominant FDC was studied for linkage analysis. A genome-wide search was undertaken after a large series of candidate genes were excluded and was then extended to two other families with autosomal dominant pattern of transmission and identical clinical features. Coinheritance of the disease gene was excluded for > 95% of the genome, after 251 polymorphic markers were analyzed. Linkage was found for chromosome 9q13-q22, with a maximum multipoint lod score of 4.2. There was no evidence of heterogeneity. The FDC locus was placed in the interval between loci D9S153 and D9S152. Several candidate genes for causing dilated cardiomyopathy map in this region.

Purification and properties of human DNA helicase VI

A novel ATP-dependent DNA unwinding enzyme, called human DNA helicase VI (HDH VI), was purified to apparent homogeneity from HeLa cells and characterized. From 327 g of cultured cells, 0.44 mg of pure enzyme was recovered, free of DNA polymerase, ligase, topoisomerase, nicking and nuclease activities. The enzyme behaves as a monomer having an M(r) of 128 kDa, whether determined with SDS-PAGE, or in native conditions. Photoaffinity labelling with [alpha-32P]ATP labelled the 128 kDa protein. Only ATP or dATP hydrolysis supports the unwinding activity for which a divalent cation (Mg2+ > Mn2+) is required. HDH VI unwinds exclusively DNA duplexes with an annealed portion < 32 bp and prefers a replication fork-like structure of the substrate. It cannot unwind blunt-end duplexes and is inactive also on DNA-RNA or RNA-RNA hybrids. HDH VI unwinds DNA unidirectionally by moving in the 3' to 5' direction along the bound strand.

Molecular and functional interactions of transcription factor USF with the long terminal repeat of human immunodeficiency virus type 1

The human transcription factor USF, purified from HeLa cells, and its recombinant 43-kDa component bind to the long terminal repeat (LTR) of human immunodeficiency virus type 1. The proteins footprint over nucleotides from position -173 to -157 upstream of the transcription start site, generating strong DNAse I hypersensitivity sites at the 3' sides on both strands. As detected by methylation protection studies, the factor forms symmetric contacts with the guanines of the palindromic CACGTG core of the recognized sequence. Its binding ability is abolished by the mutation of this core sequence and is strongly reduced by the cytosine methylation of the central CpG dinucleotide. Upon binding, both recombinant and purified USFs bend the LTR DNA template. The role of USF in the control of transcription initiation from the LTR was tested by in vitro transcription assays. Upon addition of the protein, transcription from constructs containing an intact binding site is increased, while the responsiveness in constructs with a mutated sequence is abolished. Furthermore, the addition of a decoy plasmid which contains multiple repeats of the target sequence results in downregulation of transcription from the LTR. These results suggest that USF is a positive regulator of LTR-mediated transcriptional activation.

Familial dilated cardiomyopathy

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A rapid procedure for the quantitation of low abundance RNAs by competitive reverse transcription-polymerase chain reaction

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Absence of linkage between idiopathic dilated cardiomyopathy and candidate genes involved in the immune function in a large Italian pedigree

Idiopathic dilated cardiomyopathy (IDC) is a heart disease of unknown aetiology characterised by impaired ventricular function usually associated with dilatation of the cardiac chambers. In order to test the hypothesis of an immunological cause for the disease at the genetic level, we performed linkage analysis between the putative disease locus and some of the potential candidate genes involved in the immune response or coding for the targets for autoantibodies in a large multigeneration family (63 members) from southern Italy with autosomal dominant transmission of the disease. Twenty-nine polymorphic markers on 18 different chromosomal locations were investigated, including markers linked to the genes coding for the HLA antigens, the immunoglobulin heavy and light chains, the receptors for the immunoglobulin Fc fragments, the subunits of the T cell receptor and the associated CD3, CD4, CD8, and CD45 antigens, interleukins 1, 3, 4, 5, 6, 9, and 11, the interleukin 1 and 2 receptors, and the genes coding for the beta 1 adrenoreceptor, the adenine nucleotide translocator-1, and the cardiac alpha and beta myosin heavy chains. No evidence for genetic linkage to IDC was found at any of these candidate loci. These results indicate that the still unidentified IDC gene maps outside several loci involved in the regulation of immune reactivity.

Low frequency of detection by nested polymerase chain reaction of enterovirus ribonucleic acid in endomyocardial tissue of patients with idiopathic dilated cardiomyopathy

OBJECTIVES

The purpose of this study was to determine the prevalence of enteroviral infection in the myocardium of patients with idiopathic dilated cardiomyopathy by using a highly sensitive and specific detection technique.

BACKGROUND

Recent molecular studies have suggested that enteroviral persistence (in particular, coxsackieviruses type B) may underlie idiopathic myocarditis and dilated cardiomyopathy.

METHODS

The method used to detect enterovirus-specific ribonucleic acids (RNAs) is based on reverse transcription and nested polymerase chain reaction amplification with four pairs of primers from the conserved 5' noncoding region of the enteroviral genome. Several members of the Enterovirus genus are detectable by this assay (coxsackieviruses B1 to B6; polioviruses 1 to 3; echoviruses 9, 19 and 31), with a sensitivity threshold close to the detection of a single molecule of viral RNA in 1 mg of tissue sample. Endomyocardial tissue samples from 84 subjects were analyzed (77 samples obtained from left endomyocardial biopsies, 7 from explanted hearts). The subjects comprised 63 study patients (53 with dilated cardiomyopathy, 3 with idiopathic myocarditis, 1 with right ventricular dysplasia, 1 with restrictive cardiomyopathy, 1 with eosinophilic myocarditis, 1 with primary ventricular fibrillation and 3 with myocarditis of known etiology) and 21 control subjects with other diseases.

RESULTS

Positive signals were obtained only in samples from six study patients (four with dilated cardiomyopathy, one with right ventricular dysplasia and one with myocarditis). Samples from control subjects, uninfected rat myocardium and cultured cell lines yielded systematically negative results. Moreover, the nucleotide sequence analysis of the amplification products from patients with positive samples raised doubts about the true positivity of these samples.

CONCLUSIONS

This study suggests that the persistence of enteroviral RNA in dilated cardiomyopathy is not a major cause of the disease and that a careful analysis of polymerase chain reaction amplification products is essential in any study in which this technique is pushed to high sensitivity thresholds.

Molecular genetics of dilated cardiomyopathy

The recent advances in molecular biology and genetic engineering are producing relevant results in cardiology, in particular in the field of cardiomyopathies. Molecular genetics has been used for the detection of viral genomes persisting in myocardial tissue of patients with idiopathic dilated cardiomyopathy (IDC). Very recent data, based on highly sensitive and specific technologies, suggest, however, that enterovirus persistence is not a major cause of the disease. Another application of molecular genetics is the study of the familial form of IDC, using linkage analysis as a tool for the identification of the disease gene. According to this method, the X-linked form of familial IDC has been mapped within the dystrophin gene in a series of families, and preliminary reports suggest that the mutation (or mutations) concerns the muscle-promoter region. Linkage studies on the autosomal dominant form of IDC are in progress. A possible approach is the identification of linkage between the disease and an array of "candidate genes". Preliminary data have ruled out the involvement of a series of relevant candidates genes, among which the cardiac beta-myosin heavy chain gene. An alternative approach for linkage studies is to perform a random screening of the genome, in which a large number of anonymous markers are selected and tested. In conclusion, molecular genetics is starting to provide fundamental data about the pathogenetic mechanisms of IDC. The relevance of these findings is also crucial for clinical and therapeutic implications.

A modified protocol for in vivo footprinting by ligation-mediated polymerase chain reaction

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The quest for a human ori

Attempts at identifying DNA replication origins in human cells have been performed with a variety of molecular genetic and biochemical approaches, with often controversial results. The combination of bromodeoxyuridine labelling, immunopurification of newly synthesized labelled DNA, measurement of the relative abundance of markers in this DNA by quantitative competitive PCR, has allowed the identification within 450 bp of the start-site of DNA replication located at the human lamin B2 gene. The origin is located near the non-transcribed spacer between two highly transcribed genes and shows evidence of a number of specific protein-DNA interactions, the most prominent of which disappears when the cells are differentiated into a non-proliferating state.

Searching for replication origins in mammalian DNA

The attempts at identifying precise replication origins (ori) in mammalian DNA have been pursued mainly through physico-chemical and biochemical approaches, in view of the essential failure of the search for autonomously replicating sequences in cultured cells. These approaches involve the mapping of short stretches of nascent DNA, the identification of the regions where either leading or lagging strands switch polarity, or the localization of replication intermediates by two-dimensional gel electrophoresis. Due to the complexity of animal cell genomes, most of these studies have been performed on amplified domains and with the use of synchronization procedures. The results obtained have been controversial. In order to avoid the use of experimental procedures potentially affecting the physiological mechanism of DNA replication, we have developed a method for the localization of ori in single-copy loci in exponentially growing cells. This method entails the absolute quantification of the abundance of selected DNA fragments along a genomic region within samples of newly synthesized DNA by competitive polymerase chain reaction (PCR); the latter is immune to all the uncontrollable variables which severely affect the reproducibility of conventional PCR. The application of this method to SV40 ori-driven plasmid replication precisely identifies the known ori localization. Using the same approach, we have mapped an ori for bi-directional DNA replication in a 13.7-kb locus of human chromosome 19 encoding lamin B2.

In vivo footprinting analysis of constitutive and inducible protein-DNA interactions at the long terminal repeat of human immunodeficiency virus type 1

The regulation of the rate of transcription of human immunodeficiency virus type 1 is mainly exerted through the long terminal repeat (LTR) at the 5' end of the provirus. A large number of cis-acting regulatory elements have been identified in the LTR by in vitro binding studies; the biological role of these sites within living infected cells, however, is still not clear. We have studied the interactions of nuclear proteins with the LTR in the U1 monocytic cell line by in vivo dimethylsulfate footprinting, using the ligation-mediated polymerase chain reaction technique. In this cell line, transcription of the virus, which is very low under basal conditions, is highly inducible by treatment with phorbol esters; therefore, this system is likely to represent a suitable cellular model to study viral latency. Independently of the level of viral transcription, major in vivo footprints appear at the two Sp1 sites adjacent to the enhancer, the downstream-positioned enhancer repeat, the NFAT binding site, and one of the purine-rich sites of the negative regulatory element. Upon transcriptional activation by phorbol myristate acetate, the only perturbation in the footprinting pattern is a dramatic increase in dimethylsulfate sensitivity of guanine at position -92 in the downstream enhancer repeat. This modification is correlated with the transient induction of two enhancer-binding activities, as determined by gel retardation assays. While the transcriptional rate is still increasing and the in vivo footprinting pattern is unchanged at up to 24 h postactivation, these enhancer-binding factors are considerably reduced at this time. Therefore, further levels of regulation have to be considered to explain the maintenance of the induced state.

Inhibition of heterologous DNA replication by the MVMp nonstructural NS-1 protein: identification of a target sequence

The nonstructural protein NS-1 of minute virus of mice (MVMp), an autonomous parvovirus, trans-inhibits the replication of a chimeric plasmid containing the SV40 origin of replication (ori) embedded in the MVMp genome. It appears that a 157-bp 5' proximal sequence of MVMp DNA is sufficient, in the presence of NS-1, to cause the inhibition of DNA replication driven by the SV40 ori placed on the same molecule. This effect is not dependent on the orientation of the MVMp target sequence and results from both a reduced level of utilization of SV40 ori and the blockage of progressing replication forks at the level of the target. Furthermore, replication driven by Epstein-Barr virus origin (oriP) is trans-inhibited by MVMp but this inhibition does not require the presence of parvoviral sequences in cis. On the basis of sequence homologies between EBV oriP and MVMp 5' terminal sequence, it is proposed that the direct or indirect interaction of NS-1 with parvovirus-like sequences present in heterologous viral and possibly also cellular genomes may result in an inhibition of DNA replication.