CENP-B binds a novel centromeric sequence in the Asian mouse Mus caroli.

Minor satellite DNA, found at Mus musculus centromeres, is not present in the genome of the Asian mouse Mus caroli. This repetitive sequence family is speculated to have a role in centromere function by providing an array of binding sites for the centromere-associated protein CENP-B. The apparent absence of CENP-B binding sites in the M. caroli genome poses a major challenge to this hypothesis. Here we describe two abundant satellite DNA sequences present at M. caroli centromeres. These satellites are organized as tandem repeat arrays, over 1 Mb in size, of either 60- or 79-bp monomers. All autosomes carry both satellites and small amounts of a sequence related to the M. musculus major satellite. The Y chromosome contains small amounts of both major satellite and the 60-bp satellite, whereas the X chromosome carries only major satellite sequences. M. caroli chromosomes segregate in M. caroli x M. musculus interspecific hybrid cell lines, indicating that the two sets of chromosomes can interact with the same mitotic spindle. Using a polyclonal CENP-B antiserum, we demonstrate that M. caroli centromeres can bind murine CENP-B in such an interspecific cell line, despite the absence of canonical 17-bp CENP-B binding sites in the M. caroli genome. Sequence analysis of the 79-bp M. caroli satellite reveals a 17-bp motif that contains all nine bases previously shown to be necessary for in vitro binding of CENP-B. This M. caroli motif binds CENP-B from HeLa cell nuclear extract in vitro, as indicated by gel mobility shift analysis. We therefore suggest that this motif also causes CENP-B to associate with M. caroli centromeres in vivo. Despite the sequence differences, M. caroli presents a third, novel mammalian centromeric sequence producing an array of binding sites for CENP-B.

Candida prosthetic valve endocarditis cured by caspofungin therapy without valve replacement.

A 64-year-old woman with a mechanical mitral valve prosthesis developed late-onset Candida endocarditis. Blood cultures grew Candida glabrata and Candida krusei. Transesophageal echocardiography demonstrated vegetations on the valve. The patient was not medically fit for valve replacement, but her condition was successfully treated with 6 weeks of intravenous caspofungin therapy.

Will this be the end of the anticoagulation clinic for patients with atrial fibrillation?

Atrial fibrillation is the most common clinical arrhythmia and with an ageing population, it is an increasing cause of hospital admissions, morbidity and mortality. The most feared complication of atrial fibrillation is stroke. A number of studies have demonstrated that warfarin is at least moderately effective at reducing thromboembolic risk in stroke yet its use in both the community and in secondary care is suboptimal. Concerns about drug interactions, frequent blood monitoring and the risks of over and under coagulation have led to under prescription. Direct thrombin inhibitors are under investigation as an alternative to warfarin for thromboembolic prophylaxis in atrial fibrillation. Two large studies (SPORTIF III and SPORTIF V) have recently been published examining the effectiveness of the direct thrombin inhibitor ximelagatran at reducing thromboembolic risk. Ximelagatran was shown to be non-inferior to warfarin for the prevention of thromboembolic complications. Concerns however have arisen about long-term safety, particularly the possible effects on hepatic function. This review examines the data and discusses whether the introduction of these drugs could result in the end of the anticoagulation clinic for patients with atrial fibrillation.

Pre-participation cardiovascular screening: is community screening using hand-held cardiac ultrasound feasible?

We evaluated the feasibility and costs of utilising hand-held cardiac ultrasound (HHCU) as part of a community-based pre-participation cardiovascular screening programme. Ninety-seven school children were screened using a personal history, a physical examination, a resting 12-lead electrocardiogram (ECG) and a HHCU. A consultant cardiologist independently reviewed and reported the data. Previously undiagnosed cardiovascular abnormalities were identified in nine participants (9%). An additional three participants (3%) were diagnosed with hypertension. The nine abnormalities were identified at a cost of £460 per finding, with a cost of £43 per participant screened. The marginal cost of adding a HHCU to the personal history, physical examination and ECG was £16 per participant. Pre-participation screening in the community using hand-held echocardiography is practical and inexpensive. The additional sensitivity and specificity provided by the ultrasound may enhance screening programmes, thereby reducing false positives and the need for expensive follow-up testing.

Specific interaction of mouse major satellite with MAR-binding protein SAF-A.

A DNA-binding activity specific to the major mouse satellite (satMa) has been detected in a nuclear matrix protein extract by electrophoretic mobility shift assays (EMSA) after fractionation by ion exchange chromatography. An antibody raised against the satMa-protein complexes recovered from preparative EMSA recognizes on Western blots one major polypeptide with an apparent molecular mass of 120 kDa. The protein also has a similar affinity for a matrix-associated region (MAR) fragment. We demonstrate that the protein is a murine homologue of SAF-A which has been shown to bind selectively to MARs and is responsible for the satMa-binding activity in the chromatographic fractions. SatMa has significant homology to the mouse minor satellite fragments, but its binding of SAF-A shows much less affinity. No protected regions of significant length were found by footprinting, but multiple T residues scattered within the satMa sequence are protected, indicating that the whole fragment is involved in the binding to SAF-A. Combined immunofluorescence (SAF-A) and FISH (satMa) with in situ nuclear matrix procedures reveal that SAF-A and satMa colocalize. SAF-A appears as bright dots in interphase nuclei, presumably associated with MARs, predominantly surrounding and covering heterochromatic areas. A scheme based on morphological observations and biochemical data of SAF-A double satMa/MAR specificity is discussed.

The mammalian centromere: its molecular architecture.

The DNA and protein composition of the centromeric domains in mammalian chromosomes is now relatively well characterised. The major families of repeated DNAs, i.e., the simple-sequence and alphoids in man and the satellite sequences (both minor and major) in the mouse have been sequenced and long-range maps using pulse-field gels of some centromeres have been carried out. Autoimmune antibodies have provided an insight into some of the proteins which interact with these DNA sequences. Although the individual components of the mammalian centromere may have been identified, how they interact with each other to give the functional structure visualised by electron microscopy is yet to be determined. This review examines our understanding of these separate components.

The role of pacemaker and defibrillator therapy for the treatment of atrial fibrillation.

The development of pacemaker and defibrillator technology has provided a new direction for the treatment of recurrent symptomatic atrial fibrillation (AF). Sophisticated atrial preventative pacing algorithms are now available and newer implantable devices have additional atrial termination pacing therapies. Results from studies examining the effectiveness of atrial anti-tachycardia pacing algorithms have suggested that 50% of atrial arrhythmias (including AF) can be pace terminated using these devices. The atrial defibrillator has recently been shown to be a safe and effective method of restoring and maintaining sinus rhythm in selected patients. Symptoms and quality of life can be improved and some patients demonstrate increased sinus rhythm duration (sinus rhythm begets sinus rhythm) with repeated use of the device. This review article discusses the current application of device therapy for the management of AF and explores some of the merits and limitations of these devices.

The clinical and electrophysiological implications of asymptomatic atrial fibrillation.

Atrial fibrillation (AF) is the commonest arrhythmia encountered in clinical practice and is frequently associated with significant symptoms. Asymptomatic AF may also increase the risks of heart failure, thromboembolism and cardiomyopathy but its prevalence is significantly underestimated by routine surveillance methods. The development of long-term external monitors and implantable devices has offered a new insight into the true prevalence of asymptomatic AF. Similar management strategies should be applied to both symptomatic and asymptomatic patient groups and anticoagulation should be continued indefinitely in those with a history of AF and risk factors for thromboembolism. Enhanced detection of clinically silent AF could improve outcomes but the resource implications will be significant.

Spontaneous coronary artery dissection.

We present a case of a 43-year-old lady who presented with an acute coronary syndrome, but without any cardiac risk factors or previous cardiac symptoms, and who had a spontaneous coronary artery dissection. This was successfully treated with percutaneous coronary intervention. A brief discussion of this clinical entity and literature review is presented.