Haematopoietic stem cells (HSCs) are self-renewing stem cells capable of replenishing all blood lineages. In all vertebrate embryos that have been studied, definitive HSCs are generated initially ...within the dorsal aorta (DA) of the embryonic vasculature by a series of poorly understood inductive events. Previous studies have identified that signalling relayed from adjacent somites coordinates HSC induction, but the nature of this signal has remained elusive. Here we reveal that somite specification of HSCs occurs via the deployment of a specific endothelial precursor population, which arises within a sub-compartment of the zebrafish somite that we have defined as the endotome. Endothelial cells of the endotome are specified within the nascent somite by the activity of the homeobox gene meox1. Specified endotomal cells consequently migrate and colonize the DA, where they induce HSC formation through the deployment of chemokine signalling activated in these cells during endotome formation. Loss of meox1 activity expands the endotome at the expense of a second somitic cell type, the muscle precursors of the dermomyotomal equivalent in zebrafish, the external cell layer. The resulting increase in endotome-derived cells that migrate to colonize the DA generates a dramatic increase in chemokine-dependent HSC induction. This study reveals the molecular basis for a novel somite lineage restriction mechanism and defines a new paradigm in induction of definitive HSCs.
A new phenomenon called imposed ordered structures has been of particular interest to the dusty plasma community within the past several years. These structures are a new type of pattern formation ...within a dusty plasma in which the dust particles become fixed to a background confining potential whose spatial structure is determined by some conducting element present in the plasma. In previous works, this element has typically been a conducting wire mesh. One of the unanswered questions is whether the dust particles become trapped beneath the conducting surface of the mesh or in the gaps (holes) between the wires. This work makes use of a new electrode whose shape is designed to mimic that of wire mesh, but with much larger dimensions to facilitate in situ diagnostic measurements. Observations of the dust show that particles become confined to the regions beneath the holes of this new electrode. Measurements of the dust particle velocities allow for a determination of the kinetic energy within the dust cloud which show that the particles are in an energetic steady state. Further, comparisons of spatial profiles of the particle velocities also show that the dust particles typically reside in areas of increased plasma glow, possibly being trapped by plasma filaments.
The activities and behaviours of a female head coach of a national rugby union team were recorded in both training and competition, across a whole rugby season, using the newly developed Rugby Coach ...Activities and Behaviours Instrument (RCABI). The instrument incorporates 24 categories of behaviour, embedded within three forms of activity (training form (TF), playing form (PF) and competitive match) and seven sub-activity types. In contrast to traditional drill-based coaching, 58.5% of the training time was found to have been spent in PF activities. Moreover, the proportion of PF activities increased to a peak average of 83.8% in proximity to the team's annual international championship. Uniquely, one of the coach's most prolific behaviours was conferring with associates (23.3%), highlighting the importance of interactions with assistant coaches, medical staff and others in shaping the coaching process. Additionally, the frequencies of key behaviours such as questioning and praise were found to vary between the different activity forms and types, raising questions about previous conceptions of effective coaching practice. The findings are discussed in the light of the Game Sense philosophy and the role of the head coach.
Research has shown that having meaningful occupations and active, valued social roles is important in successfully transitioning into retirement. Golf is often associated with retirees and studies ...show participation can have generic health benefits. However, this research aims to explore if golf club membership can satisfy a deeper need for meaning and social interaction in the absence of the work role. Eight retirees who were active members of a golf club participated in the study. A novel methodology was utilised, involving a five-minute writing task designed to elicit spontaneous thought about the subject of retirement. Themes derived from the writing task were used to inform semi-structured interviews. Thematic analysis of combined data from interviews and the writing task generated four themes: keeping busy, freedom from the work role, the social side of golf, and continued sense of purpose. The writing task proved successful in summoning succinct yet rich data that tapped into spontaneous and raw thoughts about retirement and should be considered for use in future qualitative work. Results demonstrate that golf club membership can offer volunteering and personal development opportunities in addition to being a place where social identity can be re-negotiated, helping to replace the social roles and meaningful occupations lost in the transition out of work.
Problem-based learning along with other game and player-centred approaches have been promoted as valuable alternatives to more traditional, skill-based, directive, and leader-centric pedagogical ...approaches. However, as research has shown, they are not unproblematic or straightforward to apply. Heeding to calls for more empirical studies of game-centred approaches in coaching contexts, this study explored the impact of a unique problem-based learning (PBL) informed academy-wide coaching approach to athlete learning and development known as Beat the Game within a top-level rugby union professional club. Drawing on Michel Foucault's (1977. Discipline and punish: The birth of the prison. Vintage) disciplinary framework, we specifically sought to critically examine whether, to what extent, and how a PBL informed academy-wide coaching approach challenges the dominant disciplinary logic of elite sport. Our data, based on observations and semi-structured interviews with three academy coaches and sixteen junior and senior academy players, showed a definitive loosening of disciplinary aspects in both training and game environments accompanied by a shift towards a less leader-centric, linear, and hierarchical understanding of leadership and decision-making. Despite these promising shifts, the application of a PBL-informed coaching approach within this elite development context also presented many challenges, not the least of which resulted from the non-alignment of academy and first team coaching approaches. Our analysis, therefore, indicated the need for more research which focuses on the short-term and long-term impact that such disconnects have on continued progression, performance, physical and mental wellbeing, and job satisfaction and longevity especially given the growing popularity of non-linear pedagogies in youth sporting contexts.
Reflection is now advocated by coach education programmes around the world as a framework for coaches to learn from their experience. Yet, there is a paucity of empirical and critical work focussed ...on coaches' experiences of reflective practice. Consequently, we lack understanding as to the utility of reflection in the messy realities of practice, and of what is meaningful to those who engage in such a personally involving, emotive and challenging process. This article presents a series of narratives that evoke the dilemmas I (the lead author) experienced reflecting on my reflective practice within an action research process. The narratives tell a highly personal tale about the temporal, emotional and contextual qualities of reflective practice, a tale that counters traditional presentations of the coach as a calculated, dispassionate and rational being who operates as if in a social vacuum. By providing insight that befits the problematic nature of practice, we hope to contribute to a more authentic and holistic epistemology in sports coaching.
The Premier League's Elite Player Performance Plan (EPPP) has transformed the ways in which young players are recruited, coached, supported and evaluated. To date, our scientific understanding of ...talent identification and development processes has been largely informed by (post)positivist studies addressing the physiological, psychological and biomechanical features of elite youth performance. In this paper, Crossley's relational theorising is presented as a heuristic device that could allow us to systematically recognise the interdependencies, ties, dialectics, and co-constituted interactions that comprise talent identification and development activities in professional football. We argue that his thesis enables us to better understand both a) the configuration and meaning making of those that comprise these relational networks, and b) the enabling and constraining features of (inter)action for these interconnected actors. For us, such knowledge can ultimately support the generation of accounts of talent identification and development that better reflect their inherently social, interactive and practical complexity.
Organ growth requires a careful balance between stem cell self-renewal and lineage commitment to ensure proper tissue expansion. The cellular and molecular mechanisms that mediate this balance are ...unresolved in most organs, including skeletal muscle. Here we identify a long-lived stem cell pool that mediates growth of the zebrafish myotome. This population exhibits extensive clonal drift, shifting from random deployment of stem cells during development to reliance on a small number of dominant clones to fuel the vast majority of muscle growth. This clonal drift requires Meox1, a homeobox protein that directly inhibits the cell-cycle checkpoint gene ccnb1. Meox1 initiates G2 cell-cycle arrest within muscle stem cells, and disrupting this G2 arrest causes premature lineage commitment and the resulting defects in muscle growth. These findings reveal that distinct regulatory mechanisms orchestrate stem cell dynamics during organ growth, beyond the G0/G1 cell-cycle inhibition traditionally associated with maintaining tissue-resident stem cells.
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•Skeletal muscle growth is driven by stem cells that exhibit extensive clonal drift•The homeobox gene meox1 controls clonal drift during muscle growth•Meox1 directly inhibits ccnb1 to arrest stem cells in G2 phase•Artificially capturing cells in G2 arrest ectopically increases Meox1+ stem cells
Currie and colleagues reveal a dramatic clonal drift of muscle stem cells during tissue growth, which is regulated at the G2 phase of the cell cycle via Meox1-dependent control of ccnb1. This contrasts with G0/G1 phase control evident in adult stem cells, indicating divergent modes of stem cell regulation.
This paper presents the results of a recent study of the interaction between charged dust particles and plasma ions through the electrostatic and ion drag forces in a dc glow discharge plasma. ...Measurements of the dust particles motion are carried out using particle image velocimetry (PIV). When an electrostatic perturbation is applied to the dust cloud, the particle motion, in response to the perturbation, is shown to reverse direction as the gas pressure is increased. An analysis of the dust particle motion and background plasma parameters suggests that there is a change in the equilibrium position and competition between the electrostatic force and the ion drag force on the particles that lead to the asymmetric motion of the cloud. The ion drag and electric forces on the dust particles are calculated at each pressure using detailed measurements of the plasma parameters, as measured by a single Langmuir probe. The analysis of these measurements suggests that the reversal of direction is a result of the change in the electric field in the plasma, but that the effectiveness of the perturbation at displacing the dust cloud is controlled by the ion drag force.
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