LvNotch signaling plays a dual role in regulating the position of the ectoderm-endoderm boundary in the sea urchin embryo

The molecular mechanisms guiding the positioning of the ectoderm-endoderm boundary along the animal-vegetal axis of the sea urchin embryo remain largely unknown. We report here a role for the sea urchin homolog of the Notch receptor, LvNotch, in mediating the position of this boundary. Overexpression of an activated form of LvNotch throughout the embryo shifts the ectoderm-endoderm boundary more animally along the animal-vegetal axis, whereas expression of a dominant negative form shifts the border vegetally. Mosaic experiments that target activated and dominant negative forms of LvNotch into individual blastomeres of the early embryo, combined with lineage analyses, further reveal that LvNotch signaling mediates the position of this boundary by distinct mechanisms within the animal versus vegetal portions of the embryo. In the animal region of the embryo, LvNotch signaling acts cell autonomously to promote endoderm formation more animally, while in the vegetal portion, LvNotch signaling also promotes the ectoderm-endoderm boundary more animally, but through a cell non-autonomous mechanism. We further demonstrate that vegetal LvNotch signaling controls the localization of nuclear β-catenin at the ectoderm-endoderm boundary. Based on these results, we propose that LvNotch signaling promotes the position of the ectoderm-endoderm boundary more animally via two mechanisms: (1) a cell-autonomous function within the animal region of the embryo, and (2) a cell non-autonomous role in the vegetal region that regulates a signal(s) mediating ectoderm-endoderm position, possibly through the control of nuclear β-catenin at the boundary

Tectonostratigraphic Evolution of the orange basin, sw Africa

The Orange Basin is a Late Jurassic to present day basin located on the volcanic-rifted passive margin of SW Africa. 2D seismic data and structural restoration techniques were used to develop a tectonostratigraphic model of the basin consisting of a syn-rift and a post-rift megasequences separated by an Early Cretaceous break-up unconformity. The post-rift megasequence is characterised by gravity tectonics where extensional faults transferred displacement downdip into a deep water fold and thrust belt (DWFTB). Gravity gliding tectonics occurred through a combination of cratonic uplift and thermal subsidence and stopped via deltaic progradation and associated differential sedimentary loading

Influence of fault geometries and mechanical anisotropies on the growth and inversion of hanging-wall synclinal basins: insights from sandbox models and natural examples

Salt is mechanically weaker than other sedimentary rocks in rift basins. It commonly acts as a strain localizer, and decouples supra- and sub-salt deformation. In the rift basins discussed in this paper, sub-salt faults commonly form wide and deep ramp synclines controlled by the thickness and strength of the overlying salt section, as well as by the shapes of the extensional faults, and the magnitudes and slip rates along the faults. Upon inversion of these rift basins, the inherited extensional architectures, and particularly the continuity of the salt section, significantly controls the later contractional deformation. This paper utilizes scaled sandbox models to analyse the interplay between sub-salt structures and supra-salt units during both extension and inversion. Series 1 experiments involved baseline models run using isotropic sand packs for simple and ramp-flat listric faults, as well as for simple planar and kinked planar faults. Series 2 experiments involved the same fault geometries but also included a pre-extension polymer layer to simulate salt in the stratigraphy. In these experiments, the polymer layer decoupled the extensional and contractional strains, and inhibited the upwards propagation of sub-polymer faults. In all Series 2 experiments, the extension produced a synclinal hanging-wall basin above the polymer layer as a result of polymer migration during the deformation. During inversion, the supra-polymer synclinal basin was uplifted, folded and detached above the polymer layer. Changes in thickness of the polymer layer during the inversion produced primary welds and these permitted the sub-polymer deformation to propagate upwards into the supra-salt layers. The experimental results are compared with examples from the Parentis Basin (Bay of Biscay), the Broad Fourteens Basin (southern North Sea), the Feda Graben (central North Sea) and the Cameros Basin (Iberian Range, Spain)

Scaled physical models of continental rifting: application to the Baikal Rift Zone

Scaled physical models constructed with dry sand layers have proven to be a useful tool for the simulation of the structural patterns that are commonly observed in natural rift systems. With this study we have tried to simulate the evolution of the Baikal Rift Zone as to get better insight in the importance of some of the processes controlling its development. For this purpose, models have been constructed with different baseplate geometries. These models allowed us to observe the possible basement controls on the present-day fault structures in the Baikal Rift Zone.Baseplates having similar shapes as the Siberian Craton caused in the models the development of the stepwise fault deflection that is characteristic for the western border fault system of Lake Baikal. During the initial evolution of the modelled faults, several relay zones were formed between isolated fault segments. Such relay zones are also common in the border fault system of Lake Baikal. In later stages of the modelling, further extension lead to the linkage between fault segments, causing the eventual disappearance of the different relay zones.The development of the models was continuously monitored using digital photographs. Animating the sequence of these photographs allowed to carefully study the kinematic evolution of the experiments. After certain amounts of extension (usually 1 or 2cm) the different basins that had formed in the models were filled with syn-kinematic sand layers. Completed models have subsequently been impregnated and sectioned either vertically or horizontally in 1cm intervals. This technique reveals the internal geometry of the formed fault structures. 3D reconstructions of the models have been produced by digitising certain reference levels on the different crosssections.Such 3D images clearly illustrate the variations in fault displacements in the different parts of the models. Moreover, 3-dimensional representations of the experiments can easily be compared with the available digital terrain models of the Baikal Rift Zone, to test the validity of the modelling results.In this study we have examined in detail the kinematic evolution and the growth of faults in different sandbox experiments, and we have compared our observations with structural interpretations that have already been made for the Baikal Rift Zone

Repeated exposure to chlorpyrifos is associated with a dose-dependent chronic neurobehavioral deficit in adult rats

Organophosphate (OP) chemicals include commonly used pesticides and chemical warfare agents, and mechanistically they are potent inhibitors of the cholinesterase (ChE) enzyme. Epidemiological studies report long-term neuropsychiatric issues, including depression and cognitive impairments in OP-exposed individuals. Chlorpyrifos (CPF) is one of the most widely used pesticides worldwide. Multiple laboratory studies have reported on either the long-term behavioral effect of an acute high-dose CPF (30-250 mg/kg) or studied sub-chronic behavioral effects, particularly the motor and cognitive effects of repeated low-dose CPF. However, studies are lacking on chronic mood and depression-related morbidities following repeated CPF doses that would mimic occupationally relevant OP exposures. In this study, adult male rats were injected with CPF (1, 3, 5, or 10 mg/kg/d, s.c.) for 21 consecutive days. Dependent on the CPF dose, ChE activity was inhibited approximately 60-80% in the blood and about 20-50% in the hippocampus at 2-days after the end of CPF exposures. Following a 12-week washout period, a complete recovery of ChE activity was noted. However, CPF-treated rats exhibited a dose-dependent increase in signs related to anhedonia (sucrose preference test), anxiety (open-field and elevated plus-maze), and despair (forced swim test) at this stage. To the best of our knowledge, this could be the first laboratory study that demonstrates a cause-effect relationship between occupational-like CPF exposures in adult rats and the development of long-term depression-related outcomes and could provide an experimental system to study molecular mechanisms underlying environmental OP exposures and the elevated risk for chronic behavioral deficits

Weld kinematics of synrift salt during basement-involved extension and subsequent inversion: Results from analog models

Scaled analog models based on extensional basins with synrift salt show how basement topography exerts a control factor on weld kinematics during the extension and inversion phases. In the case of basement-involved extension, syn-rift salt thickness differences may lead to variable degrees of extensional decoupling between basement topography and overburden, which in turn have a strong impact on the development of salt structures. With ongoing extension and after welding, the basin kinematics evolves toward a coupled deformation style. The basin architecture of our experimental results record the halokinetic activity related to growing diapirs and the timing of weld formation during extension. Moreover, the structures that result from any subsequent inversion of these basins strongly depends on the inherited welds and salt structures. While those basins are uplifted, the main contractional deformation during inversion is absorbed by the pre-existing salt structures, whose are squeezed developing secondary welds that often evolve into thrust welds. The analysis of our analog models shows that shortening of diapirs is favored by: 1) basement topography changes that induce reactivation of primary welds as thrust welds; 2) reactivation of the salt unit as a contractional detachment; and 3) synkinematic sedimentation during basin inversion. Finally in this article we also compare two natural examples from the southern North Sea that highlight deformation patterns very similar to those observed in our analog models

Repression of mesodermal fate by foxa, a key endoderm regulator of the sea urchin embryo

The foxa gene is an integral component of the endoderm specification subcircuit of the endomesoderm gene regulatory network in the Strongylocentrotus purpuratus embryo. Its transcripts become confined to veg2, then veg1 endodermal territories, and, following gastrulation, throughout the gut. It is also expressed in the stomodeal ectoderm. gatae and otx genes provide input into the pregastrular regulatory system of foxa, and Foxa represses its own transcription, resulting in an oscillatory temporal expression profile. Here, we report three separate essential functions of the foxa gene: it represses mesodermal fate in the veg2 endomesoderm; it is required in postgastrular development for the expression of gut-specific genes; and it is necessary for stomodaeum formation. If its expression is reduced by a morpholino, more endomesoderm cells become pigment and other mesenchymal cell types, less gut is specified, and the larva has no mouth. Experiments in which blastomere transplantation is combined with foxa MASO treatment demonstrate that, in the normal endoderm, a crucial role of Foxa is to repress gcm expression in response to a Notch signal, and hence to repress mesodermal fate. Chimeric recombination experiments in which veg2, veg1 or ectoderm cells contained foxa MASO show which region of foxa expression controls each of the three functions. These experiments show that the foxa gene is a component of three distinct embryonic gene regulatory networks