Data harvesting from fields of spindles.

The mitotic spindle is essential for chromosome segregation and must be large enough to accommodate all of the chromatin in the dividing cell. In this issue, Dinarina et al. (2009) grow "fields" of spindles on coverslips to investigate the relationship between chromatin and spindle size as well as intrinsic mechanisms of spindle assembly.

Protein architecture of the human kinetochore microtubule attachment site.

Chromosome segregation requires assembly of kinetochores on centromeric chromatin to mediate interactions with spindle microtubules and control cell-cycle progression. To elucidate the protein architecture of human kinetochores, we developed a two-color fluorescence light microscopy method that measures average label separation, Delta, at <5 nm accuracy. Delta analysis of 16 proteins representing core structural complexes spanning the centromeric chromatin-microtubule interface, when correlated with mechanical states of spindle-attached kinetochores, provided a nanometer-scale map of protein position and mechanical properties of protein linkages. Treatment with taxol, which suppresses microtubule dynamics and activates the spindle checkpoint, revealed a specific switch in kinetochore architecture. Cumulatively, Delta analysis revealed that compliant linkages are restricted to the proximity of chromatin, suggested a model for how the KMN (KNL1/Mis12 complex/Ndc80 complex) network provides microtubule attachment and generates pulling forces from depolymerization, and identified an intrakinetochore molecular switch that may function in controlling checkpoint activity.

[Comparative analysis of the brain distribution of [18F]FDG in populations of patients with Alzheimer's disease with or without family history of dementia]. / Analyse comparative de la distribution cérébrale du [18F]FDG dans une population de patients souffrant de maladie d'Alzheimer présentant ou non des antécédents familiaux de démence.

Hereditary forms of Alzheimer's disease (AD) and early-onset forms have more brain damage than sporadic or late-onset forms at the time of diagnosis (1, 2). Data in the literature are contradictory concerning familial forms without known heredity or mutation. The aim of this study was to compare the brain distribution of FDG between two populations of patients with a clinical diagnosis of sporadic AD according to the presence or not of a first degree family history of dementia. We retrospectively included 243 patients with clinical diagnosis of AD who underwent brain FDG PET imaging between 2012 and 2017. SPM12 was used to compare the FDG brain distribution in 199 patients with AD and no familial history of dementia and 43 patients with AD and first degree familial history of dementia. Compared to a database of 22 healthy control subjects, both groups of AD patients showed a significant decrease of FDG distribution in temporo-parietal, posterior cingulate and posterior left frontal cortex with respect to the controls (p inferior to 0.05 corrected for the family-wise error, pFWE-corr). There were no significant differences between the two AD groups (pFWE-corr superior to 0.05 and p superior to 0.001 uncorrected for multiple comparisons) that present the same brain metabolic pathology.

Les formes héréditaires de la maladie d'Alzheimer (MA) et les formes à début précoce présentent une atteinte cérébrale plus importante que les formes sporadiques ou celles à début tardif au moment du diagnostic (1, 2). Les données de la littérature sont contradictoires en ce qui concerne les formes familiales sans hérédité ni mutation connue. L'objectif de cette étude était de comparer la distribution cérébrale du [18F]fluoro-2-deoxy-D-glucose ([18F]FDG) entre deux populations de patients présentant un diagnostic clinique de la MA sporadique selon la présence, ou non, d'une histoire familiale de démence au premier degré. Dans cette étude rétrospective, nous avons inclus 243 patients vus entre 2012 et 2017. Le logiciel SPM12 a été utilisé pour comparer la distribution cérébrale du FDG entre 199 patients souffrant de MA, sans histoire familiale et 43 patients souffrant de MA avec une histoire familiale de démence au premier degré. Comparés à une base de données de 22 sujets contrôles sains, chacun des deux groupes de patients présentait une réduction significative de la distribution du FDG au niveau du cortex temporo-pariétal, cingulaire postérieur et frontal postérieur gauche (p inf�rieur a 0,05 corrigé pour le family-wise error, pFWE-corr), caractéristique de la maladie. Il n'y avait pas de différence significative entre les deux groupes MA (pFWE-corr sup�rieur a 0,05 et p sup�rieur a 0,001 non corrigé, pour des comparaisons multiples) qui présentent donc la même altération métabolique cérébrale.

Data set of healthy old people assessed for three walking conditions using accelerometric and opto-electronic methods.

BACKGROUND: Gait patterns of healthy aging are needed to allow a comparison with pathological situations. However, little data is available. OBJECTIVE: To present gait pattern of healthy older specially selected to be "healthy walkers". METHOD: Fifty-seven older people benefited from a geriatric assessment including clinical and functional evaluations to include only those without gait disorders. Gait data were simultaneously recorded using a tri-axial accelerometer placed on the waist and four 3D position markers placed on the feet at the level of the heel and the toe. Volunteers walked at comfortable self-selected speed (CW), fast self-selected speed (FW), and finally in dual task walking condition (DTW). The extracted gait parameters were: gait speed, stride length, stride frequency, regularity and symmetry, swing, stance and double support time and ratio and minimum toe clearance. Gait speed and stride length were normalized to the right leg length. RESULTS: Fifty-seven older people with a mean age of 69.7 ± 4.2 years old (range from 65 to 82 years) were included. Data were analyzed according to the gender and according to the age (<70 or ≥70 years old). After normalization to leg length, the main significant differences were shown for stride length and minimum toe clearance in CW, FW and in DTW that were shorter in women. The regularity in FW was significantly lower among older volunteers. CONCLUSIONS: This work provides a data set considering 14 gait parameters obtained from 57 healthy old people strictly selected and assessed for three walking conditions and shows that GS, SL and MTC have to be related to the gender. The age-related impact on gait performances appears reduced in this cohort.

[Conversion disorder : functional neuroimaging and neurobiological mechanisms]. / Vignette diagnostique de l'étudiant. Trouble de conversion : neuroimagerie fonctionnelle et mécanismes neurobiologiques.

Conversion disorder is a psychiatric disorder often encountered in neurology services. This condition without organic lesions was and still is sometimes referred as an imaginary illness or feigning. However, the absence of organic lesions does not exclude the possibility of cerebral dysfunction. The etiologic mechanisms underlying this disorder remain uncertain even today.The advent of cognitive and functional imaging opens up a field of exploration for psychiatry in understanding the neurobiological mechanisms underlying mental disorders and especially the conversion disorder. This article reports several neuroimaging studies of conversion disorder and attempts to generate hypotheses about neurobiological mechanisms.

Le trouble de conversion est une pathologie psychiatrique fréquemment rencontrée dans les services de neurologie. Cette pathologie «sans substrat¼ a été et est encore parfois qualifiée de maladie imaginaire ou de simulation. Cependant, l'absence de substrat «organique¼ n'exclut pas la possibilité d'un dysfonctionnement cérébral. Les mécanismes étiopathogéniques qui sous-tendent ce trouble sont longtemps restés incertains, encore aujourd'hui. L'avènement des sciences cognitives et de l'imagerie fonctionnelle ouvre un champ d'exploration pour la psychiatrie dans la compréhension des mécanismes neurobiologiques qui sous-tendent les troubles mentaux et, en particulier, le trouble de conversion. Cet article reprend plusieurs études de neuroimagerie sur le trouble de conversion et tente d'en dégager des hypothèses sur ses mécanismes neurobiologiques.

Gait speed or gait variability, which one to use as a marker of risk to develop Alzheimer disease? A pilot study.

BACKGROUND: Previous literature demonstrates the interest of gait analysis to predict cognitive decline in old people. AIMS: This pilot study aims to determine if gait speed or gait variability is a marker able to early identify, among mild cognitive impairment (MCI) subjects, those at risk to develop Alzheimer's disease (AD) in the future. METHODS: 13 MCI subjects were included in 2007. Their gait parameters (walking speed, stride length and gait frequency, regularity and symmetry) were measured in 2007 and 2008 in simple task (ST) and in dual task (DT) using a triaxial accelerometer (Locometrix(®)). Among the 13 MCI subjects included in 2007, 10 were assessed in 2008. So, 23 (13 in 2007 + 10 in 2008) gait tests were collected. In 2011, MCI people were considered as "MCI+" when they developed AD (between baseline and 2011) and as "MCI-" if they did not. Among the 23 gait tests, 15 were from MCI+ (9 gait tests in 2007 and 6 in 2008) and 8 from MCI- (4 gait tests in 2007 and 4 gait tests in 2008). Mann-Whitney non-parametric U test was used to compare gait parameters of MCI+ and MCI-. RESULTS: Gait speed, symmetry and regularity were lower in MCI+ than in MCI-. DISCUSSION: Despite the small sample size, the results presented in this original pilot study are in line as the infrequent previous literature related to this topic. The authors discuss lacks and strengths of this work. CONCLUSIONS: These results suggest that both gait speed and gait variability could be markers to early identify MCI at risk to develop AD.

The KMN protein network--chief conductors of the kinetochore orchestra.

Successful completion of mitosis requires that sister kinetochores become attached end-on to the plus ends of spindle microtubules (MTs) in prometaphase, thereby forming kinetochore microtubules (kMTs) that tether one sister to one spindle pole and the other sister to the opposite pole. Sites for kMT attachment provide at least four key functions: robust and dynamic kMT anchorage; force generation that can be coupled to kMT plus-end dynamics; correction of errors in kMT attachment; and control of the spindle assembly checkpoint (SAC). The SAC typically delays anaphase until chromosomes achieve metaphase alignment with each sister kinetochore acquiring a full complement of kMTs. Although it has been known for over 30 years that MT motor proteins reside at kinetochores, a highly conserved network of protein complexes, called the KMN network, has emerged in recent years as the primary interface between the kinetochore and kMTs. This Commentary will summarize recent advances in our understanding of the role of the KMN network for the key kinetochore functions, with a focus on human cells.

Esperanto for histones: CENP-A, not CenH3, is the centromeric histone H3 variant.

The first centromeric protein identified in any species was CENP-A, a divergent member of the histone H3 family that was recognised by autoantibodies from patients with scleroderma-spectrum disease. It has recently been suggested to rename this protein CenH3. Here, we argue that the original name should be maintained both because it is the basis of a long established nomenclature for centromere proteins and because it avoids confusion due to the presence of canonical histone H3 at centromeres.

[The effect of normal and pathological aging on cognition]. / Les effets du vieillissement normal et pathologique sur la cognition.

Cognitive deficits in the executive and memory domains are observed in normal aging and Alzheimer's disease (AD). These deficits are associated with changes at the brain activity level. However, a series of factors are prone to delay the occurrence of cognitive deficits, such as mental stimulation or physical activity. Similarly, cognitive rehabilitation allows improving the daily life functioning of patients with AD. The identification of factors and techniques that contribute to maintain cognitive efficiency and/or counteract the effects of AD will allow optimizing quality of life of older people.

[Clinical study of the month: depressive pseudo-dementia]. / Le cas clinique du mois. Pseudo-démence dépressive.

We report the case of a man aged 62 suffering from a known type I bipolar disorder and referred by his attending psychiatrist because of a state of spatiotemporal disorientation, confusion and prostration evoking significant neurologic impairment. The interest of this case report is in the use of the 18-FDG PET-Scanner, which is increasingly widespread in clinical psychiatry, to support the differential diagnosis between a psycho-organic pathology like dementia or a functional psychiatric pathology like depressive pseudo-dementia (also named melancholic dementia), in which some patterns of dysfunction can now be identified by functional imaging.

[Dementia, end of life and euthanasia]. / Troubles cognitifs, fin de vie et euthanasia.

Among legislative criteria granting the right to practice euthanasia or assisted suicide, there are systematically four major elements. Precisely, any request must be voluntary, persistent, to be well thought and well informed. Such euthanasia raises numerous difficult questions in case of dementia. It also justifies thinking about possibilities that can offer specific arrangements of anticipated demands in such peculiar cases. Empirical experiences show us that it applies with difficulties in practice. Finally, to avoid that a big majority of these demands would find themselves not applied in practice, it would certainly be necessary to add to it structural valuation of advance care planning, and assure its recognition and development. These should not be limited to a single pathological target but would address all of us to increase advance care planning initiation, which remains the most limiting factor of such any early but continuous procedure.

Welcome to a new kind of tension: translating kinetochore mechanics into a wait-anaphase signal.

Recent high-resolution studies of kinetochore structure have transformed the way researchers think about this crucial macro-molecular complex, which is essential for ensuring chromosome segregation occurs faithfully during cell division. Kinetochores mediate the interaction between chromosomes and the plus-ends of dynamic spindle microtubules and control the timing of anaphase onset by regulating the spindle assembly checkpoint (SAC). There is much debate in the SAC research community as to whether mitotic cells sense only microtubule attachment at the kinetochore, or both attachment and tension, before committing to anaphase. In this Commentary, we present a brief history of the tension-versus-attachment debate, summarize recent advances in our understanding of kinetochore structure and focus on the implications of a phenomenon known as intrakinetochore stretch for SAC regulation. We also hypothesize how intrakinetochore stretch might impact SAC function by regulating both microtubule attachment stability and the localization and activity of checkpoint components at the kinetochore.

Pericentric chromatin is organized into an intramolecular loop in mitosis.

BACKGROUND: Cohesin proteins link sister chromatids and provide the basis for tension between bioriented sister chomatids in mitosis. Cohesin is concentrated at the centromere region of the chromosome despite the fact that sister centromeres can be separated by 800 nm in vivo. The function of cohesin at sites of separated DNA is unknown. RESULTS: We provide evidence that the kinetochore promotes the organization of pericentric chromatin into a cruciform in mitosis such that centromere-flanking DNA adopts an intramolecular loop, whereas sister-chromatid arms are paired intermolecularly. Visualization of cohesin subunits by fluorescence microscopy revealed a cylindrical structure that encircles the central spindle and spans the distance between sister kinetochores. Kinetochore assembly at the apex of the loop initiates intrastrand loop formation that extends approximately 25 kb (12.5 kb on either side of the centromere). Two centromere loops (one from each sister chromatid) are stretched between the ends of sister-kinetochore microtubules along the spindle axis. At the base of the loop there is a transition to intermolecular sister-chromatid pairing. CONCLUSIONS: The C loop conformation reveals the structural basis for sister-kinetochore clustering in budding yeast and for kinetochore biorientation and thus resolves the paradox of maximal interstrand separation in regions of highest cohesin concentration.

A novel approach to the study of hypoxia-ischemia-induced clinical and subclinical seizures in the neonatal rat.

Perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality and chronic neurologic morbidity in infants and children. HIE is the most common cause of neonatal seizures, and seizure activity in neonates can be clinical, with both EEG and behavioral symptoms, subclinical with only EEG activity, or just behavioral. The accurate detection of these different seizure manifestations and the extent to which they differ in their effects on the neonatal brain continues to be a concern in neonatal medicine. Most experimental studies of the interaction between hypoxia-ischemia (HI) and seizures have utilized a chemical induction of seizures, which may be less clinically relevant. Here, we expanded our model of unilateral cerebral HI in the immature rat to include video EEG and electromyographic recording before, during and after HI in term-equivalent postnatal-day-12 rats. We observed that immature rats display both clinical and subclinical seizures during the period of HI, and that the total number of seizures and time to first seizure correlate with the extent of tissue damage. We also tested the feasibility of developing an automated seizure detection algorithm for the unbiased detection and characterization of the different types of seizure activity observed in this model.

Pathways of spindle assembly.

Recent studies have revealed that, in some systems, chromatin has the ability to stabilize microtubules and organize them into bipolar spindles independently of kinetochores and centrosomes. In addition, several molecules have been identified recently that are necessary for spindle assembly; these include proteins that regulate microtubule dynamics, proteins that organize microtubule minus ends into spindle poles, and members of the kinesin superfamily that reside on the chromosome arms.

Positive feedback interactions between microtubule and actin dynamics during cell motility.

The migration of tissue cells requires interplay between the microtubule and actin cytoskeletal systems. Recent reports suggest that interactions of microtubules with actin dynamics creates a polarization of microtubule assembly behavior in cells, such that microtubule growth occurs at the leading edge and microtubule shortening occurs at the cell body and rear. Microtubule growth and shortening may activate Rac1 and RhoA signaling, respectively, to control actin dynamics. Thus, an actin-dependent gradient in microtubule dynamic-instability parameters in cells may feed back through the activation of specific signalling pathways to perpetuate the polarized actin-assembly dynamics required for cell motility.

Mitosis: a history of division.

Mitosis has been studied since the early 1880s, to the extent that we now have a detailed, but still incomplete, description of spindle dynamics and mechanics, a sense of potential mechanochemical and regulatory mechanisms at a molecular level, and a long list of mitotic proteins. Here we present a personal view of how far we have come, and where we need to go to fully understand the mechanisms involved in mitosis.

The polarity and dynamics of microtubule assembly in the budding yeast Saccharomyces cerevisiae.

Microtubule assembly in Saccharomyces cerevisiae is initiated from sites within spindle pole bodies (SPBs) in the nuclear envelope. Microtubule plus ends are thought to be organized distal to the SPBs, while minus ends are proximal. Several hypotheses for the function of microtubule motor proteins in force generation and regulation of microtubule assembly propose that assembly and disassembly occur at minus ends as well as at plus ends. Here we analyse microtubule assembly relative to the SPBs in haploid yeast cells expressing green fluorescent protein fused to alpha-tubulin, a microtubule subunit. Throughout the cell cycle, analysis of fluorescent speckle marks on cytoplasmic astral microtubules reveals that there is no detectable assembly or disassembly at minus ends. After laser-photobleaching, metaphase spindles recover about 63% of the bleached fluorescence, with a half-life of about 1 minute. After anaphase onset, photobleached marks in the interpolar spindle are persistent and do not move relative to the SPBs. In late anaphase, the elongated spindles disassemble at the microtubule plus ends. These results show for astral and anaphase interpolar spindle microtubules, and possibly for metaphase spindle microtubules, that microtubule assembly and disassembly occur at plus, and not minus, ends.

Microtubule growth activates Rac1 to promote lamellipodial protrusion in fibroblasts.

Microtubules are involved in actin-based protrusion at the leading-edge lamellipodia of migrating fibroblasts. Here we show that the growth of microtubules induced in fibroblasts by removal of the microtubule destabilizer nocodazole activates Rac1 GTPase, leading to the polymerization of actin in lamellipodial protrusions. Lamellipodial protrusions are also activated by the rapid growth of a disorganized array of very short microtubules induced by the microtubule-stabilizing drug taxol. Thus, neither microtubule shortening nor long-range microtubule-based intracellular transport is required for activating protrusion. We suggest that the growth phase of microtubule dynamic instability at leading-edge lamellipodia locally activates Rac1 to drive actin polymerization and lamellipodial protrusion required for cell migration.

Nuclear congression is driven by cytoplasmic microtubule plus end interactions in S. cerevisiae.

Nuclear movement before karyogamy in eukaryotes is known as pronuclear migration or as nuclear congression in Saccharomyces cerevisiae. In this study, S. cerevisiae is used as a model system to study microtubule (MT)-dependent nuclear movements during mating. We find that nuclear congression occurs through the interaction of MT plus ends rather than sliding and extensive MT overlap. Furthermore, the orientation and attachment of MTs to the shmoo tip before cell wall breakdown is not required for nuclear congression. The MT plus end-binding proteins Kar3p, a class 14 COOH-terminal kinesin, and Bik1p, the CLIP-170 orthologue, localize to plus ends in the shmoo tip and initiate MT interactions and depolymerization after cell wall breakdown. These data support a model in which nuclear congression in budding yeast occurs by plus end MT capture and depolymerization, generating forces sufficient to move nuclei through the cytoplasm. This is the first evidence that MT plus end interactions from oppositely oriented organizing centers can provide the force for organelle transport in vivo.