DNA circles promote yeast ageing in part through stimulating the reorganization of nuclear pore complexes.

The nuclear pore complex (NPC) mediates nearly all exchanges between nucleus and cytoplasm, and in many species, it changes composition as the organism ages. However, how these changes arise and whether they contribute themselves to ageing is poorly understood. We show that SAGA-dependent attachment of DNA circles to NPCs in replicatively ageing yeast cells causes NPCs to lose their nuclear basket and cytoplasmic complexes. These NPCs were not recognized as defective by the NPC quality control machinery (SINC) and not targeted by ESCRTs. They interacted normally or more effectively with protein import and export factors but specifically lost mRNA export factors. Acetylation of Nup60 drove the displacement of basket and cytoplasmic complexes from circle-bound NPCs. Mutations preventing this remodeling extended the replicative lifespan of the cells. Thus, our data suggest that the anchorage of accumulating circles locks NPCs in a specialized state and that this process is intrinsically linked to the mechanisms by which ERCs promote ageing.

Induced aneuploidy in neural stem cells triggers a delayed stress response and impairs adult life span in flies.

Studying aneuploidy during organism development has strong limitations because chronic mitotic perturbations used to generate aneuploidy usually result in lethality. We developed a genetic tool to induce aneuploidy in an acute and time-controlled manner during Drosophila development. This is achieved by reversible depletion of cohesin, a key molecule controlling mitotic fidelity. Larvae challenged with aneuploidy hatch into adults with severe motor defects shortening their life span. Neural stem cells, despite being aneuploid, display a delayed stress response and continue proliferating, resulting in the rapid appearance of chromosomal instability, a complex array of karyotypes, and cellular abnormalities. Notably, when other brain-cell lineages are forced to self-renew, aneuploidy-associated stress response is significantly delayed. Protecting only the developing brain from induced aneuploidy is sufficient to rescue motor defects and adult life span, suggesting that neural tissue is the most ill-equipped to deal with developmental aneuploidy.

Absence of the Spindle Assembly Checkpoint Restores Mitotic Fidelity upon Loss of Sister Chromatid Cohesion.

The fidelity of mitosis depends on cohesive forces that keep sister chromatids together. This is mediated by cohesin that embraces sister chromatid fibers from the time of their replication until the subsequent mitosis [1-3]. Cleavage of cohesin marks anaphase onset, where single chromatids are dragged to the poles by the mitotic spindle [4-6]. Cohesin cleavage should only occur when all chromosomes are properly bio-oriented to ensure equal genome distribution and prevent random chromosome segregation. Unscheduled loss of sister chromatid cohesion is prevented by a safeguard mechanism known as the spindle assembly checkpoint (SAC) [7, 8]. To identify specific conditions capable of restoring defects associated with cohesion loss, we screened for genes whose depletion modulates Drosophila wing development when sister chromatid cohesion is impaired. Cohesion deficiency was induced by knockdown of the acetyltransferase separation anxiety (San)/Naa50, a cohesin complex stabilizer [9-12]. Several genes whose function impacts wing development upon cohesion loss were identified. Surprisingly, knockdown of key SAC proteins, Mad2 and Mps1, suppressed developmental defects associated with San depletion. SAC impairment upon cohesin removal, triggered by San depletion or artificial removal of the cohesin complex, prevented extensive genome shuffling, reduced segregation defects, and restored cell survival. This counterintuitive phenotypic suppression was caused by an intrinsic bias for efficient chromosome biorientation at mitotic entry, coupled with slow engagement of error-correction reactions. Thus, in contrast to SAC's role as a safeguard mechanism for mitotic fidelity, removal of this checkpoint alleviates mitotic errors when sister chromatid cohesion is compromised.

A quantitative analysis of cohesin decay in mitotic fidelity.

Sister chromatid cohesion mediated by cohesin is essential for mitotic fidelity. It counteracts spindle forces to prevent premature chromatid individualization and random genome segregation. However, it is unclear what effects a partial decline of cohesin may have on chromosome organization. In this study, we provide a quantitative analysis of cohesin decay by inducing acute removal of defined amounts of cohesin from metaphase-arrested chromosomes. We demonstrate that sister chromatid cohesion is very resistant to cohesin loss as chromatid disjunction is only observed when chromosomes lose >80% of bound cohesin. Removal close to this threshold leads to chromosomes that are still cohered but display compromised chromosome alignment and unstable spindle attachments. Partial cohesin decay leads to increased duration of mitosis and susceptibility to errors in chromosome segregation. We propose that high cohesin density ensures centromeric chromatin rigidity necessary to maintain a force balance with the mitotic spindle. Partial cohesin loss may lead to chromosome segregation errors even when sister chromatid cohesion is fulfilled.

Centromeric Cohesin: Molecular Glue and Much More.

Sister chromatid cohesion, mediated by the cohesin complex, is a prerequisite for faithful chromosome segregation during mitosis. Premature release of sister chromatid cohesion leads to random segregation of the genetic material and consequent aneuploidy. Multiple regulatory mechanisms ensure proper timing for cohesion establishment, concomitant with DNA replication, and cohesion release during the subsequent mitosis. Here we summarize the most important phases of the cohesin cycle and the coordination of cohesion release with the progression through mitosis. We further discuss recent evidence that has revealed additional functions for centromeric localization of cohesin in the fidelity of mitosis in metazoans. Beyond its well-established role as "molecular glue", centromeric cohesin complexes are now emerging as a scaffold for multiple fundamental processes during mitosis, including the formation of correct chromosome and kinetochore architecture, force balance with the mitotic spindle, and the association with key molecules that regulate mitotic fidelity, particularly at the chromosomal inner centromere. Centromeric chromatin may be thus seen as a dynamic place where cohesin ensures mitotic fidelity by multiple means.

Role of prediabetes in stroke.

Stroke is one of the leading causes of death and probably the greatest cause of adult disability worldwide. Diabetes mellitus (DM) is a state of accelerated aging of blood vessels. Patients with diabetes have increased risk of stroke. Hyperglycemia represents a risk factor for poor outcome following stroke, and probably is just a marker of poor outcome rather than a cause. Lowering of blood glucose levels has not been shown to improve prognosis. Also, prevention of stroke risk among patients with DM is not improved with therapy for reduction of glucose levels. On the other hand, prediabetes, a metabolic state between normal glucose metabolism and diabetes, is a risk factor for the development of DM type 2 and subsequently for stroke. Several methods are known to identify prediabetes patients, including fasting plasma glucose levels, 2-hour post load glucose levels, and glycosylated hemoglobin levels. In this text, we tried to summarize known data about diagnosis, epidemiology, risk factors, pathophysiology, and prevention of prediabetes in relation to DM and stroke.

Premature Sister Chromatid Separation Is Poorly Detected by the Spindle Assembly Checkpoint as a Result of System-Level Feedback.

Sister chromatid cohesion, mediated by the cohesin complex, is essential for faithful mitosis. Nevertheless, evidence suggests that the surveillance mechanism that governs mitotic fidelity, the spindle assembly checkpoint (SAC), is not robust enough to halt cell division when cohesion loss occurs prematurely. The mechanism behind this poor response is not properly understood. Using developing Drosophila brains, we show that full sister chromatid separation elicits a weak checkpoint response resulting in abnormal mitotic exit after a short delay. Quantitative live-cell imaging approaches combined with mathematical modeling indicate that weak SAC activation upon cohesion loss is caused by weak signal generation. This is further attenuated by several feedback loops in the mitotic signaling network. We propose that multiple feedback loops involving cyclin-dependent kinase 1 (Cdk1) gradually impair error-correction efficiency and accelerate mitotic exit upon premature loss of cohesion. Our findings explain how cohesion defects may escape SAC surveillance.

Centromere-independent accumulation of cohesin at ectopic heterochromatin sites induces chromosome stretching during anaphase.

Pericentric heterochromatin, while often considered as "junk" DNA, plays important functions in chromosome biology. It contributes to sister chromatid cohesion, a process mediated by the cohesin complex that ensures proper genome segregation during nuclear division. Long stretches of heterochromatin are almost exclusively placed at centromere-proximal regions but it remains unclear if there is functional (or mechanistic) importance in linking the sites of sister chromatid cohesion to the chromosomal regions that mediate spindle attachment (the centromere). Using engineered chromosomes in Drosophila melanogaster, we demonstrate that cohesin enrichment is dictated by the presence of heterochromatin rather than centromere proximity. This preferential accumulation is caused by an enrichment of the cohesin-loading factor (Nipped-B/NIPBL/Scc2) at dense heterochromatic regions. As a result, chromosome translocations containing ectopic pericentric heterochromatin embedded in euchromatin display additional cohesin-dependent constrictions. These ectopic cohesion sites, placed away from the centromere, disjoin abnormally during anaphase and chromosomes exhibit a significant increase in length during anaphase (termed chromatin stretching). These results provide evidence that long stretches of heterochromatin distant from the centromere, as often found in many cancers, are sufficient to induce abnormal accumulation of cohesin at these sites and thereby compromise the fidelity of chromosome segregation.

Neurosarcoidosis: two case reports with multiple cranial nerve involvement and review of the literature.

BACKGROUND: Involvement of the central nervous system is registered in a relatively small number of patients with sarcoidosis. In this article we present two cases with various neurological symptoms that fulfill criteria for neurosarcoidosis (NS). In addition, we review the literature on NS with special attention to isolated cranial nerve involvement. METHODS AND RESULTS: First patient: Neurological examination identified multiple cranial neuropathy, moderate right-sided hemiparesis, polyradiculoneuritis of the lower limbs and positive meningeal signs. Laboratory tests showed serum and cerebrospinal fluid (CSF) inflammatory abnormalities, with increased values of the angiotensin-converting enzyme (ACE). CSF analysis also showed presence of 9 oligoclonal IgG bands. Brain and spine magnetic resonance imaging (MRI) revealed diffuse meningopathy, and focal granulomatous lesion in the body of the L5 vertebra. Lung sarcoidosis was confirmed by additional diagnostic procedures. The patient was treated with Methylprednisolone and a tapering course of oral Prednisone, which reduced the pain in the back and legs and improved the strength of the right leg. However, the other neurological deficiencies remained. After confirming lung sarcoidosis, the patient received Methotrexate in addition to Prednisone but during the following 2 years the patient's condition progressively worsened and ended in death. Second patient: Neurological findings showed weakness of the right n. oculomotorius and the right n. trochlearis, as well as the right-side face weakness. We found raised level of the ACE in serum and CSF. Thorax high-definition computed tomography (HDCTT) showed ribbon-like domains of discrete changes in the pulmonary parenchyma. MRI of the brain showed multiple white matter lesions. This patient also received Methylprednisolone followed by Prednisone, and after two months, ocular motility normalized. CONCLUSION: The diagnosis of NS is always a challenge. For this rerason definitive diagnosis requires the exclusion of other causes of neuropathy. Multiple cranial neuropathies should always arouse suspicion of NS.

Clinical manifestations, diagnostic criteria and therapy of Hashimoto's encephalopathy: report of two cases.

Hashimoto's encephalopathy (HE) is a rare, still not well understood, autoimmune disease with neurological and psychiatric manifestations. and elevated titers of antithyroid antibodies in serum and cerebrospinal fluid (CSF) as a hallmark of the disease. Patients are mostly women. Current diagnostic criteria include corticosteroide responsiveness, but it is the case in only 50% of patients with HE. In steroid non-responders other immunomodulatory therapies or plasmapheresis could be applied. Disease course can be acute, subacute, chronic or relapsing-remitting. Two distinct forms emerged from the reported cases: a vasculitic type characterized by multiple relapsing-remitting stroke-like episodes and mild cognitive impairment and a diffuse progressive type characterized by dementia and psychiatric symptoms. Both forms may be accompanied by depressed level of consciousness (stupor or coma), tremor, seizures, or myoclonus. We present two patients with two distinct forms of HE who had different clinical manifestations and response to therapy.

[Significance of the combined tests application in serum and liquor of patients with suspected neurosyphilis].

BACKGROUND: :Tertiary syphilis develops in 8-40% of untreated patients. It is most commonly manifested in the form of neurosyphilis, which can be asymptomatic taking the form of tabes dorsalis or progressive paralyze. Nowadays, in the developed countries, progressive paralyze is a rather rare disease, although the incidence of this disease has been rising within the last decades. CASE REPORT: We reported a 74-year-old male with the clinical image of dementia showing psychotic symptoms. On cytobiochemical examination of cerebrospinal liquor, hyper-proteinorhacmia of 0.70 g/1l with the normal number of cells was revealed. Computed tomography of the brain showed the marked cortical cerebral and cerebellar reduction changes with multiple ischemic lesions. Within a routine examination of patients with demention, we performed serologic reactions to syphilis out of which the Veneral Disease Researc Laboratory (VDRL) test in serum and liquor was unreactive, while the Treponema pallidum hemagglutination (TPNA) test in serum and liquor was positive. Positivity in serum and liquor was additionally confirmed by the Western blot method and fluoroscent treponema antibody (FTA) test. The treatment with benzathine fenylpenicilline 2.4 g once weekly resulted in significant improving the psychotic symptoms of the disease even after two weeks. CONCLUSION: This case report showed that within the differential diagnostics in patients with demention or psychotic disorder it is obligatory to consider syphilis of the nervous system, as well as to apply a combination of various tests which, besides the typical liquor findings, significantly improve the accuracy of diagnosis. Such approach is especially important regarding the fact that neurosyphilis can remain clinically quite asymptomatic for a long period, which could lead to late therapy, while, on the contrary, an adequate and timely treatment can contribute to a significant recovery of any patients.