BAF complex-mediated chromatin relaxation is required for establishment of X chromosome inactivation

The process of epigenetic silencing, while fundamentally important, is not yet completely understood. Here we report a replenishable female mouse embryonic stem cell (mESC) system, Xmas, that allows rapid assessment of X chromosome inactivation (XCI), the epigenetic silencing mechanism of one of the two X chromosomes that enables dosage compensation in female mammals. Through a targeted genetic screen in differentiating Xmas mESCs, we reveal that the BAF complex is required to create nucleosome-depleted regions at promoters on the inactive X chromosome during the earliest stages of establishment of XCI. Without this action gene silencing fails. Xmas mESCs provide a tractable model for screen-based approaches that enable the discovery of unknown facets of the female-specific process of XCI and epigenetic silencing more broadly.Andrew Keniry ... Jose M. Polo ... et al

Social learning in LEADER: Exogenous, endogenous and hybrid evaluation in rural development

This paper considers the relationship between the centralised exogenous, institutions and the embedded, endogenous institutions of rural governance in Europe through an examination the evaluation procedures of the European LEADER programme. LEADER is presented in the literature as progressive in terms of innovation and stakeholder engagement. Yet while the planning and management of LEADER embraces heterogeneity and participation, programmatic evaluation is centralised and held at arms length from delivery organisations. The paper reviews previous efforts to improve evaluation in LEADER and considers alternative strategies for evaluation, contrasting LEADER practice with participatory evaluation methodologies in the wider international context. Can evaluation in itself be valuable as a mode of social learning and hence a driver for endogenous development in rural communities in Europe? The paper concludes by examining the challenges in producing a hybrid form of evaluation which accommodates endogenous and exogenous values

Resolving complexities associated with the timing of macroscopic folds in multiply deformed terrains: The Spring Hill synform, Vermont

Determining the timing of macroscopic folds of bedding in multiply deformed terrains is difficult, especially for rocks that have undergone a succession of overprinting near-orthogonal deformations. The Spring Hill synform in southeast Vermont is an example of such a fold. The origin and timing of this structure has been the subject of several previous studies; understanding its development is crucial to unraveling orogenesis in the Vermont Appalachians. The fold formed during a deformation path that involved a succession of overprinting near-orthogonal deformations that produced matrix fabrics S3, S4, and S5. These foliations developed with subvertical, subhorizontal, and subvertical orientations, respectively, before being rotated by the effects of younger deformations. The Spring Hill synform is generally thought to have formed as a recumbent structure during regional nappe development, S4 developing as an axial planar foliation. However, we demonstrate that the Spring Hill synform developed as a fold with a steeply dipping axial plane that was overprinted by S4 and S5. Although this geometry and overprinting history are consistent with a D3 time of formation, we can find no change in the asymmetry of pre-S3 foliations across the fold. We suggest that the synform may have formed at a much earlier stage in the orogen's history and was subsequently modified and rotated to its present geometry by the long history of west-to-east shortening that dominated the later stages of Acadian orogenesis in southeast Vermont

The Dossier of Patermouthis, Son of Lak

Papyrologie in contex

Measurement and correlation of microstructures: the case of foliation intersection axes

Recent studies have used the relative rotation axis of sigmoidal and spiral-shaped inclusion trails, known as Foliation Inflexion/Intersection Axis (FIA), to investigate geological processes such as fold mechanisms and porphyroblast growth. The geological usefulness of this method depends upon the accurate measurement of FIA orientations and correct correlation of temporally related FIAs. This paper uses new data from the Canton Schist to assess the variation in FIA orientations within and between samples, and evaluates criteria for correlating FIAs. For the first time, an entire data set of FIA measurements is published, and data are presented in a way that reflects the variation in FIA orientations within individual samples and provides an indication of the reliability of the data. Analysis of 61 FIA trends determined from the Canton Schist indicate a minimum intrasample range in FIA orientations of 30°. Three competing models are presented for correlation of these FIAs, and each of the models employ different correlation criteria. Correlation of FIAs in Model 1 is based on relative timing and textural criteria, while Model 2 uses relative timing, orientation and patterns of changing FIA orientations, and Model 3 uses relative timing and FIA orientation as correlation criteria. Importantly, the three models differ in the spread of FIA orientations within individual sets, and the number of sets distinguished in the data. Relative timing is the most reliable criterion for correlation, followed by textural criteria and patterns of changing FIA orientations from core to rim of porphyroblasts. It is proposed that within a set of temporally related FIAs, the typical spread of orientations involves clustering of data in a 60° range, but outliers occur at other orientations including near-normal to the peak distribution. Consequently, in populations of FIA data that contain a wide range of orientations, correlation on the basis of orientation is unreliable in the absence of additional criteria. The results of this study suggest that FIAs are best used as semiquantitative indicators of bulk trends rather than an exact measurement for the purpose of quantitative analyses

Superposition of gold mineralisation on pre-existing carbonate alteration: structural evidence from the Mulgarrie gold deposit, Yilgarn Craton

Carbonate alteration at the Mulgarrie gold mine in the Eastern Goldfields of Western Australia, is represented by porphyroblasts, veins and pervasive, texturally destructive, carbonatisation. Two foliations, S1M and S2M, were produced by two separate deformation events at the mine-scale, D1M and D2M. D1M and D2M both occurred in response to regional D2 tectonism. Carbonate alteration was the product of two separate episodes of fluid ingress: the earlier produced magnesite and the latter Fe-dolomite. Both periods of carbonate alteration occurred pre- to early syn-D2M, when mafic to ultramafic komatiitic rocks reacted with fluids that moved along regional faults and pre-date the alteration associated with regional peak metamorphism. Gold at Mulgarrie overprints pre- and late syn-D2 quartz veins in zones of massive carbonate alteration, suggesting it has a late- to post-D2 timing. This late timing agrees with the generally accepted syn-D3 (and younger) age for gold mineralisation in the Eastern Goldfields. We suggest that carbonate alteration at Mulgarrie is not a product of the hydrothermal event responsible for the gold mineralisation. Rather, the different relative timing of magnesite, Fe-dolomite and gold indicates there were two carbonate-producing fluid systems and a fluid transporting the gold overprinted these. Similarly, early carbonate alteration may play a role in localising auriferous vein deposits throughout the Yilgarn and other Archaean cratons

Superposition of gold mineralisation on pre-existing carbonate alteration: structural evidence from the Mulgarrie gold deposit, Yilgarn Craton

Carbonate alteration at the Mulgarrie gold mine in the Eastern Goldfields of Western Australia, is represented by porphyroblasts, veins and pervasive, texturally destructive, carbonatisation. Two foliations, S1M and S2M, were produced by two separate deformation events at the mine-scale, D1M and D2M. D1M and D2M both occurred in response to regional D2 tectonism. Carbonate alteration was the product of two separate episodes of fluid ingress: the earlier produced magnesite and the latter Fe-dolomite. Both periods of carbonate alteration occurred pre- to early syn-D2M, when mafic to ultramafic komatiitic rocks reacted with fluids that moved along regional faults and pre-date the alteration associated with regional peak metamorphism. Gold at Mulgarrie overprints pre- and late syn-D2 quartz veins in zones of massive carbonate alteration, suggesting it has a late- to post-D2 timing. This late timing agrees with the generally accepted syn-D3 (and younger) age for gold mineralisation in the Eastern Goldfields. We suggest that carbonate alteration at Mulgarrie is not a product of the hydrothermal event responsible for the gold mineralisation. Rather, the different relative timing of magnesite, Fe-dolomite and gold indicates there were two carbonate-producing fluid systems and a fluid transporting the gold overprinted these. Similarly, early carbonate alteration may play a role in localising auriferous vein deposits throughout the Yilgarn and other Archaean cratons

Early formed regional antiforms and synforms that fold younger matrix schistosities: their effect on sites of mineral growth

In the metamorphic cores of many orogenic belts, large macroscopic folds in compositional layering also appear to fold one or more pervasive matrix foliations. The latter geometry suggests the folds formed relatively late in the tectonic history, after foliation development. However, microstructural analysis of four examples of such folds suggests this is not the case. The folds formed relatively early in the orogenic history and are the end product of multiple, near orthogonal, overprinting bulk shortening events. Once large macroscopic folds initiate, they may tighten further during successive periods of sub-parallel shortening, folding or reactivation of foliations that develop during intervening periods of near orthogonal shortening. Reactivation of the compositional layering defining the fold limbs causes foliation to be rotated into parallelism with the limbs. \ud Multiple periods of porphyroblast growth accompanied the multiple phases of deformation that postdated the initial development of these folds. Some of these phases of deformation were attended by the development of large numbers of same asymmetry spiral-shaped inclusion trails in porphyroblasts on one limb of the fold and not the other, or larger numbers of opposite asymmetry spirals on the other limb, or similar numbers of the same asymmetry spirals on both limbs. Significantly, the largest disparity in numbers from limb to limb occurred for the first of these cases. For all four regional folds examined, the structural relationships that accompanied these large disparities were identical. In each case the shear sense operating on steeply dipping foliations was opposite to that required to originally develop the fold. Reactivation of the folded compositional layering was not possible for this shear sense. This favoured the development of sites of approximately coaxial shortening early during the deformation history, enhancing microfracture and promoting the growth of porphyroblasts on this limb in comparision to the other. These distributions of inclusion trail geometries from limb to limb cannot be explained by porphyroblast rotation, or folding of pre-existing rotated porphyroblasts within a shear zone, but can be explained by development of the inclusion trails synchronous with successive sub-vertical and sub-horizontal foliations.\u

On the development of gneiss domes

The New England Appalachians contain some of the first documented gneiss domes. The classic domes of SE Vermont are typical of these structures in that they appear to have formed by doming of both the gneissosity in basement gneisses and the dominant matrix schistosity in the overlying rocks, after these foliations had formed. However, the three matrix foliations (other than bedding) present in these rocks, which include the one parallel to all compositional layering, post date dome development. The domes formed as upright anticlines after deposition of the overlying Lower Palaeozoic sediments and volcanics on a PreCambrian granitic or gneissic basement. This occurred during orogenesis driven by horizontally directed compressional forces with interspersed periods of relatively coaxial gravitational collapse, rather than through early nappe development followed by folding or diapiric granite emplacement, or crustal extension and upwards bowing of a necked portion of the crust. In spite of numerous subsequent deformations, the domes are very old structures that have been little modified at the level of current crustal exposure. The dominant process during each deformation was reactivation of the compositional layering or gneissosity on at least one limb of the dome. This destroyed earlier developed crenulation cleavages that lay oblique to the compositional layering and commonly prevented new ones from developing. Consequently, a schistosity parallel to bedding in the overlying rocks, and the gneissosity below, formed and was intensified by reactivation on at least one limb of the dome during all subsequent deformations. Nappe development, which has commonly been proposed as the origin of foliation parallel to bedding in the rocks overlying gneiss domes, is not necessary and there is no evidence for such a deformation history preserved within either the bedding or matrix foliations that have been folded around the Chester and Athens domes of SE Vermont. Sub-horizontally dipping foliations that formed during collapse stages of orogenesis have mainly been the product of relatively coaxial deformation rather than the highly non-coaxial deformation that accompanies nappe development. The fold to the west of the Chester and Athens domes, which has classically been regarded as the nose of the major nappe, formed with an upright rather than shallowly dipping axial plane