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1.
J Public Health (Oxf) ; 41(3): 561-565, 2019 09 30.
Article in English | MEDLINE | ID: mdl-30007299

ABSTRACT

This article considers the role of responsibility in public health promotion. Efforts to tackle non-communicable diseases which focus on changing individual behaviour and reducing risk factor exposure sometimes invoke individual responsibility for adopting healthy lifestyles. We provide a critical discussion of this tendency. First, we outline some key distinctions in the philosophical literature on responsibility, and indicate how responsibility is incorporated into health promotion policies in the UK. We argue that the use of some forms of responsibility in health promotion is inappropriate. We present an alternative approach to understanding how individuals can 'take responsibility' for their health, based on the concept of prudence (i.e. acting in one's interests). In this discussion, we do not prescribe or proscribe specific health promotion policies. Rather, we encourage public health professionals to consider how underlying assumptions (in this case, relating to responsibility) can shape health promotion policy, and how alternative framings (such as a shift from encouraging individual responsibility to facilitating prudence) may justify different kinds of action, for instance, shaping environments to make healthy behaviours easier, rather than using education as a tool to encourage responsible behaviour.


Subject(s)
Health Policy , Health Promotion , Healthy Lifestyle , Social Responsibility , Health Behavior , Humans , Public Health , United Kingdom
2.
Nature ; 564(7734): 87-90, 2018 12.
Article in English | MEDLINE | ID: mdl-30487601

ABSTRACT

The passage of time is tracked by counting oscillations of a frequency reference, such as Earth's revolutions or swings of a pendulum. By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity, with the current generation of optical atomic clocks reporting fractional performance below the 10-17 level1-5. However, the theory of relativity prescribes that the passage of time is not absolute, but is affected by an observer's reference frame. Consequently, clock measurements exhibit sensitivity to relative velocity, acceleration and gravity potential. Here we demonstrate local optical clock measurements that surpass the current ability to account for the gravitational distortion of space-time across the surface of Earth. In two independent ytterbium optical lattice clocks, we demonstrate unprecedented values of three fundamental benchmarks of clock performance. In units of the clock frequency, we report systematic uncertainty of 1.4 × 10-18, measurement instability of 3.2 × 10-19 and reproducibility characterized by ten blinded frequency comparisons, yielding a frequency difference of [-7 ± (5)stat ± (8)sys] × 10-19, where 'stat' and 'sys' indicate statistical and systematic uncertainty, respectively. Although sensitivity to differences in gravity potential could degrade the performance of the clocks as terrestrial standards of time, this same sensitivity can be used as a very sensitive probe of geopotential5-9. Near the surface of Earth, clock comparisons at the 1 × 10-18 level provide a resolution of one centimetre along the direction of gravity, so the performance of these clocks should enable geodesy beyond the state-of-the-art level. These optical clocks could further be used to explore geophysical phenomena10, detect gravitational waves11, test general relativity12 and search for dark matter13-17.

3.
Obes Sci Pract ; 4(3): 283-288, 2018 Jun.
Article in English | MEDLINE | ID: mdl-29951219

ABSTRACT

OBJECTIVES: Although monitoring is considered a key component of effective behaviour change, the development of apps has allowed consumers to constantly evaluate their own diet, with little examination of what this might mean for eating behaviour. The aim of this study was to investigate whether self-monitoring of diet using the app MyFitnessPal or daily self-weighing increases the reported occurrence of eating disorders in adults with overweight/obesity following a weight loss programme. METHODS: Two hundred fifty adults with body mass index ≥ 27 kg/m2 received diet and exercise advice and were randomized to one of four monitoring strategies (daily self-weighing, MyFitnessPal, brief monthly consults or self-monitoring hunger) or control for 12 months. The Eating Disorder Examination Questionnaire 6.0 was used to assess eating disorder symptoms and behaviours for the previous 28 d at 0 and 12 months. RESULTS: There were no significant differences in the global Eating Disorder Examination Questionnaire score or the subscales between those in the four monitoring groups and the control at 12 months (all p ≥ 0.164), nor were there differences in binge eating, self-induced vomiting, laxative misuse or excessive exercise at 12 months (p ≥ 0.202). The overall prevalence of one or more episodes of binge eating was 53.6% at baseline and 50.6% at 12 months, with no change over time (p = 0.662). CONCLUSIONS: There was no evidence that self-monitoring, including using diet apps like MyFitnessPal or daily self-weighing, increases the reported occurrence of eating disorder behaviours in adults with overweight/obesity who are trying to lose weight.

4.
Phys Rev Lett ; 120(18): 183201, 2018 May 04.
Article in English | MEDLINE | ID: mdl-29775346

ABSTRACT

We demonstrate the absence of a dc Stark shift in an ytterbium optical lattice clock. Stray electric fields are suppressed through the introduction of an in-vacuum Faraday shield. Still, the effectiveness of the shielding must be experimentally assessed. Such diagnostics are accomplished by applying high voltage to six electrodes, which are grounded in normal operation to form part of the Faraday shield. Our measurements place a constraint on the dc Stark shift at the 10^{-20} level, in units of the clock frequency. Moreover, we discuss a potential source of error in strategies to precisely measure or cancel nonzero dc Stark shifts, attributed to field gradients coupled with the finite spatial extent of the lattice-trapped atoms. With this consideration, we find that Faraday shielding, complemented with experimental validation, provides both a practically appealing and effective solution to the problem of dc Stark shifts in optical lattice clocks.

5.
Psychol Med ; 48(2): 337-346, 2018 Jan.
Article in English | MEDLINE | ID: mdl-28705261

ABSTRACT

BACKGROUND: Social media presents an important means for social interaction, especially among adolescents, with Instagram being the most popular platform in this age-group. Pictures and communication about non-suicidal self-injury (NSSI) can frequently be found on the internet. METHODS: During 4 weeks in April 2016, n = 2826 (from n = 1154 accounts) pictures which directly depicted wounds on Instagram were investigated. Those pictures, associated comments, and user accounts were independently rated for content. Associations between characteristics of pictures and comments as well as weekly and daily trends of posting behavior were analyzed. RESULTS: Most commonly, pictures depicted wounds caused by cutting on arms or legs and were rated as mild or moderate injuries. Pictures with increasing wound grades and those depicting multiple methods of NSSI generated elevated amounts of comments. While most comments were neutral or empathic with some offering help, few comments were hostile. Pictures were mainly posted in the evening hours, with a small peak in the early morning. While there was a slight peak of pictures being posted on Sundays, postings were rather evenly spread across the week. CONCLUSIONS: Pictures of NSSI are frequently posted on Instagram. Social reinforcement might play a role in the posting of more severe NSSI pictures. Social media platforms need to take appropriate measures for preventing online social contagion.


Subject(s)
Reinforcement, Social , Self-Injurious Behavior/psychology , Skin/injuries , Social Media/statistics & numerical data , Adolescent , Adult , Child , Empathy , Female , Humans , Interpersonal Relations , Male , Photography , Social Perception , Young Adult
6.
AJNR Am J Neuroradiol ; 38(6): 1242-1247, 2017 Jun.
Article in English | MEDLINE | ID: mdl-28408626

ABSTRACT

BACKGROUND AND PURPOSE: Declines in both functional activation and functional connectivity have been reported in patients with sickle cell disease. In this study, we derived the functional and default mode responses to a word stem paradigm in age-, ethnicity-, and background-matched subjects with sickle cell disease and control groups, with the aim of testing whether both networks were similarly attenuated and whether the changes were related to physiologic parameters that characterize sickle cell disease. MATERIALS AND METHODS: Both the functional and default mode responses were obtained from age- and background-matched controls and the sickle cell population by using a visually presented word stem paradigm on a 3T scanner. RESULTS: We observed an attenuated response to both activation and deactivation in the sickle cell disease group. There were no significant differences in the activation response between the 2 groups for the contrast control > sickle cell disease; however, significant differences were observed in the medial parietal cortex, the auditory cortex, and the angular gyrus for the default mode. For the sickle cell group, a significant correlation between the activation z scores and the physiologic parameters was observed; for the deactivation, the results were not significant but the trend was similar. CONCLUSIONS: The results indicate that the physiologic parameters modulate the activation in the expected fashion, but that the effect was weaker for deactivation. Given that significant differences between the 2 groups were only seen for deactivation, additional factors must modulate the deactivation in sickle cell disease.


Subject(s)
Anemia, Sickle Cell/physiopathology , Nerve Net/physiopathology , Adolescent , Anemia, Sickle Cell/diagnostic imaging , Anemia, Sickle Cell/psychology , Auditory Cortex/diagnostic imaging , Auditory Cortex/physiopathology , Brain Mapping , Child , Female , Gyrus Cinguli/diagnostic imaging , Gyrus Cinguli/physiopathology , Humans , Image Processing, Computer-Assisted , Magnetic Resonance Imaging , Male , Nerve Net/diagnostic imaging , Neuropsychological Tests , Oxygen/blood , Parietal Lobe/diagnostic imaging , Parietal Lobe/physiopathology , Prospective Studies
7.
Psychol Med ; 47(11): 1893-1905, 2017 Aug.
Article in English | MEDLINE | ID: mdl-28397633

ABSTRACT

Children and adolescents are a vulnerable group to develop post-traumatic stress symptoms after natural or man-made disasters. In the light of increasing numbers of refugees under the age of 18 years worldwide, there is a significant need for effective treatments. This meta-analytic review investigates specific psychosocial treatments for children and adolescents after man-made and natural disasters. In a systematic literature search using MEDLINE, EMBASE and PsycINFO, as well as hand-searching existing reviews and contacting professional associations, 36 studies were identified. Random- and mixed-effects models were applied to test for average effect sizes and moderating variables. Overall, treatments showed high effect sizes in pre-post comparisons (Hedges' g = 1.34) and medium effect sizes as compared with control conditions (Hedges' g = 0.43). Treatments investigated by at least two studies were cognitive-behavioural therapy (CBT), eye movement desensitization and reprocessing (EMDR), narrative exposure therapy for children (KIDNET) and classroom-based interventions, which showed similar effect sizes. However, studies were very heterogenic with regard to their outcomes. Effects were moderated by type of profession (higher level of training leading to higher effect sizes). A number of effective psychosocial treatments for child and adolescent survivors of disasters exist. CBT, EMDR, KIDNET and classroom-based interventions can be equally recommended. Although disasters require immediate reactions and improvisation, future studies with larger sample sizes and rigorous methodology are needed.


Subject(s)
Disasters , Psychotherapy/methods , Stress Disorders, Post-Traumatic/therapy , Survivors/psychology , Adolescent , Child , Humans
8.
Phys Rev Lett ; 119(25): 253001, 2017 Dec 22.
Article in English | MEDLINE | ID: mdl-29303326

ABSTRACT

Optical clocks benefit from tight atomic confinement enabling extended interrogation times as well as Doppler- and recoil-free operation. However, these benefits come at the cost of frequency shifts that, if not properly controlled, may degrade clock accuracy. Numerous theoretical studies have predicted optical lattice clock frequency shifts that scale nonlinearly with trap depth. To experimentally observe and constrain these shifts in an ^{171}Yb optical lattice clock, we construct a lattice enhancement cavity that exaggerates the light shifts. We observe an atomic temperature that is proportional to the optical trap depth, fundamentally altering the scaling of trap-induced light shifts and simplifying their parametrization. We identify an "operational" magic wavelength where frequency shifts are insensitive to changes in trap depth. These measurements and scaling analysis constitute an essential systematic characterization for clock operation at the 10^{-18} level and beyond.

9.
Phys Rev Lett ; 116(11): 113001, 2016 Mar 18.
Article in English | MEDLINE | ID: mdl-27035299

ABSTRACT

We observe interaction-induced broadening of the two-photon 5s-18s transition in ^{87}Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly 2 orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with blackbody induced population in nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms.

10.
Nutr Metab (Lond) ; 12: 22, 2015.
Article in English | MEDLINE | ID: mdl-26075007

ABSTRACT

BACKGROUND: "Hunger training", which aims to teach people to eat only when blood glucose is below a set target, appears promising as a weight loss strategy. As the ability of participants to adhere to the rigorous protocol has been insufficiently described, we sought to determine the feasibility of hunger training, in terms of retention in the study, adherence to measuring blood glucose, and eating only when blood glucose concentrations are below a set level of 4.7 mmol/L. METHOD: We undertook a two-week feasibility study, utilising an adaptive design approach where the specific blood glucose cut-off was the adaptive feature. A blood glucose cut-off of 4.7 mmol/L (protocol A) was used for the first 20 participants. A priori we decided that if interim analysis revealed that this cut-off did not meet our feasibility criteria, the remaining ten participants would use an individualised cut-off based on their fasting glucose concentrations (protocol B). RESULTS: Retention of the participants in the study was 97 % (28/29 participants), achieving our criterion of 85 %. Participants measured their blood glucose before 94 % (95 % CI 91, 98) of eating occasions (criterion 80 %). However, participants following protocol A, which used a standard blood glucose cut-off of 4.7 mmol/L, were only able to adhere to eating when blood glucose was below the prescribed level 66 % of the time, below our within-person criterion of 75 %. By contrast, those participants following protocol B (individualised cut-off) adhered to the eating protocol 84 % of the time, a significant (p = 0.010) improvement over protocol A. CONCLUSION: Hunger training appears to be a feasible method, at least in the short-term, when an individualised fasting blood glucose is used to indicate that a meal can begin.

11.
Science ; 348(6234): 540-4, 2015 May 01.
Article in English | MEDLINE | ID: mdl-25931552

ABSTRACT

The interplay of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study nonequilibrium magnetization dynamics in an extended two-dimensional (2D) system by loading effective spin-1/2 bosons into a spin-dependent optical lattice and use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a nonequilibrium antiferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the parameters associated with superexchange and tunneling. With tunneling off-resonantly suppressed, we observe superexchange-dominated dynamics over two orders of magnitude in magnetic coupling strength. Our experiment will serve as a benchmark for future theoretical work as the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques.

12.
AJNR Am J Neuroradiol ; 33(11): 2043-9, 2012 Dec.
Article in English | MEDLINE | ID: mdl-22595904

ABSTRACT

BACKGROUND AND PURPOSE: Ischemic injury to the brain is a common complication of SCA. To better understand the neurologic impact of SCA, TBSS were applied to DTI data to investigate white matter injuries in pediatric patients with SCA. MATERIALS AND METHODS: TBSS comparisons of a range of anisotropy and diffusion measures were carried out between age- and background-matched population groups: patients with SCA with no visible lesions, patients with SCA with mild gliosis, and normal controls. RESULTS: TBSS analysis revealed that both SCA populations exhibited reduced anisotropy and increased diffusivity compared with normal controls in multiple brain regions, including the corpus callosum and centrum semiovale. Furthermore, the results suggest that the severity of SCA is positively correlated with the white matter changes in the corpus callosum. CONCLUSIONS: The study demonstrates that TBSS is a viable technique in detecting subtle white matter damage in patients with SCA whose conventional anatomic MR imaging scans show no, or minimal, abnormalities and has the potential to evaluate the neurologic impact of the treatment of SCA.


Subject(s)
Anemia, Sickle Cell/pathology , Brain/pathology , Diffusion Magnetic Resonance Imaging/methods , Mass Screening/methods , Nerve Fibers, Myelinated/pathology , Adolescent , Female , Humans , Male
13.
Bioresour Technol ; 103(1): 405-14, 2012 Jan.
Article in English | MEDLINE | ID: mdl-22023969

ABSTRACT

A 1 kg/h auger reactor utilizing mechanical mixing of steel shot heat carrier was used to pyrolyze red oak wood biomass. Response surface methodology was employed using a circumscribed central composite design of experiments to optimize the system. Factors investigated were: heat carrier inlet temperature and mass flow rate, rotational speed of screws in the reactor, and volumetric flow rate of sweep gas. Conditions for maximum bio-oil and minimum char yields were high flow rate of sweep gas (3.5 standard L/min), high heat carrier temperature (∼600 °C), high auger speeds (63 RPM) and high heat carrier mass flow rates (18 kg/h). Regression models for bio-oil and char yields are described including identification of a novel interaction effect between heat carrier mass flow rate and auger speed. Results suggest that auger reactors, which are rarely described in literature, are well suited for bio-oil production. The reactor achieved liquid yields greater than 73 wt.%.


Subject(s)
Bioreactors , Biotechnology/instrumentation , Biotechnology/methods , Hot Temperature , Biomass , Models, Chemical , Plant Oils/chemistry , Regression Analysis , Waste Products/analysis , Zea mays/chemistry
14.
Bioresour Technol ; 103(1): 374-80, 2012 Jan.
Article in English | MEDLINE | ID: mdl-22036914

ABSTRACT

A central composite design of experiments was performed to optimize a free-fall reactor for the production of bio-oil from red oak biomass. The effects of four experimental variables including heater set-point temperature, biomass particle size, sweep gas flow rate and biomass feed rate were studied. Heater set-point temperature ranged from 450 to 650 °C, average biomass particle size from 200 to 600 µm, sweep gas flow rate from 1 to 5 sL/min and biomass feed rate from 1 to 2 kg/h. Optimal operating conditions yielding over 70 wt.% bio-oil were identified at a heater set-point temperature of 575 °C, while feeding red oak biomass sized less than 300 µm at 2 kg/h into the 0.021 m diameter, 1.8m tall reactor. Sweep gas flow rate did not have significant effect on bio-oil yield over the range tested.


Subject(s)
Bioreactors , Biotechnology/instrumentation , Biotechnology/methods , Plant Oils/metabolism , Quercus/chemistry , Temperature , Biomass , Gases , Models, Chemical , Particle Size , Rheology
15.
Eur J Clin Nutr ; 65(1): 117-24, 2011 Jan.
Article in English | MEDLINE | ID: mdl-20877394

ABSTRACT

BACKGROUND/OBJECTIVES: Diets high in nuts reduce cholesterol, probably due to their favorable lipid profile and other bioactive substances. However, the physical form of the nut may be important as the cell wall of intact nuts may limit the hypocholesterolemic effect of nuts by reducing lipid bioavailability. Therefore, we investigated the effects on blood lipids of incorporating three different forms of hazelnuts (ground, sliced and whole) into the usual diet. SUBJECTS/METHODS: In a randomized crossover study with three phases, 48 mildly hypercholesterolemic participants were asked to consume 30 g of ground, sliced or whole hazelnuts for 4 weeks. Body weight, plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triacylglycerol (TAG), apolipoprotein (apo) A1, apo B100 and α-tocopherol were measured at baseline and at the end of each dietary phase. RESULTS: There were no significant differences in any outcome variable between the different forms of nuts (all P ≥ 0.159). However, compared with baseline, mean values at the end of each hazelnut intervention were significantly higher for HDL-C (P = 0.023) and α-tocopherol (P = 0.005), and significantly lower for TC (P < 0.001), LDL-C (P < 0.001), TC:HDL-C ratio (P <0 .001), apo B100 (P = 0.002) and apo B100:apo A1 ratio (P < 0.001), with no significant difference in body weight (P = 0.813). CONCLUSIONS: The ingestion of three different forms of hazelnuts equally improved the lipoprotein profile and α-tocopherol concentrations in mildly hypercholesterolemic individuals. Hazelnuts can therefore be incorporated into the usual diet as a means of reducing cardiovascular disease risk.


Subject(s)
Cholesterol, HDL/blood , Cholesterol, LDL/blood , Corylus , Hypercholesterolemia/diet therapy , Triglycerides/blood , alpha-Tocopherol/blood , Adult , Apolipoprotein A-I/blood , Apolipoprotein B-100/blood , Body Weight , Cross-Over Studies , Diet , Female , Humans , Linear Models , Male , Middle Aged
16.
Eur J Clin Nutr ; 64(2): 224-6, 2010 Feb.
Article in English | MEDLINE | ID: mdl-19935822

ABSTRACT

A crossover study was designed to determine whether the fat and carbohydrate contents of evening meals consumed the night preceding glycaemic index (GI) testing had an effect on the GI. Twenty participants consumed two different evening meals in which the energy contributions from fat, carbohydrate and protein were in the ratio 50:30:15 and 25:60:15, respectively. Each participant completed eight tests that involved two evening meals with different macronutrient compositions followed the next morning by two treatments, glucose beverage or fruit bread, all carried out in duplicate. The GI of fruit bread was determined on the mornings following each of the evening meals. The GIs (95% CI) were 68 (60, 76) and 59 (52, 67) after the high-carbohydrate and high-fat meals, respectively, and were not different (P=0.11). Thus, varying the fat and carbohydrate contents of the evening meal before GI testing the next morning did not affect the GI.


Subject(s)
Blood Glucose/metabolism , Dietary Carbohydrates/pharmacology , Dietary Fats/pharmacology , Glycemic Index , Adult , Area Under Curve , Cross-Over Studies , Dietary Proteins , Energy Intake , Female , Humans , Male , Time Factors , Young Adult
17.
Eur J Clin Nutr ; 63(5): 692-4, 2009 May.
Article in English | MEDLINE | ID: mdl-18398423

ABSTRACT

A randomized crossover study was carried out to determine whether moderate alcohol consumption the night preceding glycaemic index testing has an effect on glycaemic response. Test foods consisted of two glucose beverages and two bread samples, containing 50 g of available carbohydrate. Each test food was consumed with and without alcohol the night preceding testing. Glucose concentration was measured over 2 h and area under the curve (AUC) determined. The AUC for bread and glucose without and with alcohol did not differ for either the glucose drink (ratio (95% confidence intervals): 1.00 (0.8, 1.1)) or bread (0.9; (0.8, 1.1)). Further, there was no difference in the glycaemic index (GI) of the bread with and without alcohol (64 (6) vs 67 (2)%; P=0.78). Moderate alcohol consumption the evening before GI testing does not affect glycaemic response or GI determination.


Subject(s)
Alcohol Drinking , Glucose/metabolism , Glycemic Index/drug effects , Adult , Area Under Curve , Bread , Cross-Over Studies , Diet , Ethanol/pharmacology , Female , Humans , Male , Young Adult
18.
Am J Bot ; 95(6): 664-71, 2008 Jun.
Article in English | MEDLINE | ID: mdl-21632391

ABSTRACT

Extant liverworts are "living fossils" considered sister to all other plants and as such provide clues to the evolution of the microtubule organizing center (MTOC) in anastral cells. This report is the first on microtubule arrays and their γ-tubulin-nucleating sites during meiosis in a member of the Ricciales, a specialized, species-rich group of complex thalloid (marchantioid) liverworts. In meiotic prophase, γ-tubulin becomes concentrated at several sites adjacent to the nuclear envelope. Microtubules organized at these foci give rise to a multipolar prometaphase spindle. By metaphase I, the spindle has matured into a bipolar structure with truncated poles. In both first and second meiosis, γ-tubulin forms box-like caps at the spindle poles. γ-Tubulin moves from spindle poles to the proximal surfaces of telophase chromosomes where interzonal microtubules are nucleated. Although a phragmoplast is organized, no cell plate is deposited, and second division occurs simultaneously in the undivided sporocyte. γ-Tubulin surrounds each of the tetrad nuclei, and phragmoplasts initiated between both sister and nonsister nuclei direct simultaneous cytokinesis. The overall pattern of meiosis (unlobed polyplastidic sporocytes, nuclear envelope MTOC, multipolar spindle origin, spindles with box-like poles, and simultaneous cytokinesis) more closely resembles that of Conocephalum than other marchantiod liverworts.

20.
Protoplasma ; 227(2-4): 77-85, 2006 May.
Article in English | MEDLINE | ID: mdl-16736249

ABSTRACT

Meiosis in Aneura pinguis is preceded by extensive cytoplasmic preparation for quadripartitioning of the diploid sporocyte into a tetrad of haploid spores. In early prophase the four future spore domains are defined by lobing of the cytoplasm and development of a quadripolar prophase spindle focused at polar organizers (POs) centered in the lobes. Cells entering the reproductive phase become isolated and, instead of hooplike cortical microtubules, have endoplasmic microtubule systems centered on POs. These archesporial cells proliferate by mitosis before entering meiosis. In prophase of each mitosis, POs containing a distinct concentration of gamma-tubulin appear de novo at tips of nuclei and initiate the bipolar spindle. Cells entering meiosis become transformed into quadrilobed sporocytes with four POs, one in each lobe. This transition is a complex process encompassing assembly of two opposite POs which subsequently disperse into intersecting bands of microtubules that form around the central nucleus. The girdling bands define the future planes of cytokinesis and the cytoplasm protrudes through the restrictive bands becoming quadrilobed. Two large POs reappear in opposite cleavage furrows. Each divides and the resulting POs migrate into the tetrahedral lobes of cytoplasm. Cones of microtubules emanating from the four POs interact to form a quadripolar microtubule system (QMS) that surrounds the nucleus in meiotic prophase. The QMS is subsequently transformed into a functionally bipolar metaphase spindle by migration of poles in pairs to opposite cleavage furrows. These findings contribute to knowledge of microtubule organization and the role of microtubules in spatial regulation of cytokinesis in plants.


Subject(s)
Bryophyta/cytology , Bryophyta/metabolism , Cell Polarity , Meiosis , Microtubules/metabolism , Tubulin/metabolism , Spores/cytology
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