MATHEMATICAL MODELING OF THE HYDRAULIC DRIVE OF THE SECTIONS OF A WIDE-COLLECTING CULTIVATOR WITH SEQUENTIAL ACTIVATION OF HYDRAULIC CYLINDERS

The publication discusses the issues of mathematical modeling of dynamic processes occurring in a complex hydromechanical system of the hydraulic drive of the wide-cut cultivator sections with consistent wear of the hydraulic cylinders. The analysis of known designs of wide-cutting tools and agricultural units is carried out. It is noted that one of the tendencies in the development of domestic agricultural engineering is an increase in the width of coverage of tillage machines. In this regard, hydraulic drives for decomposition and assembly of sections of these machines are widely used. The use of this type of drive is due to its compactness, speed and power. The basic schematic diagrams of hydraulic drives for decomposition of wide-cut tillage machines are considered. On the basis of the analysis, a schematic diagram of the hydraulic drive for assembling (decomposing) sections of a wide-grip cultivator with sequential actuation of hydraulic cylinders is proposed and the principle of its operation is described. A mathematical model has been developed for the hydraulic drive of the wide-grip cultivator sections in the working and transport position. The mathematical model consists of the equations of the continuity of the flows of the working fluid, which describe the processes occurring in the hydraulic drive, and the equations of moments and forces, from which it is possible to determine the force factors acting on the elements of the system. It is difficult to obtain an analytical solution to the resulting system of equations, therefore, to find solutions, numerous methods were applied, namely the Runge-Kutta-Feldberg method with an automatic change in the integration step. On the basis of the obtained dependencies, an analysis of the operation of the hydraulic drive with sequential wear of the hydraulic cylinders was carried out and recommendations were proposed on the design device and directions for improving the hydraulic drive of the tillage unit sections.

REST/NRSF drives homeostatic plasticity of inhibitory synapses in a target-dependent fashion

The repressor-element 1-silencing transcription/neuron-restrictive silencer factor (REST/NRSF) controls hundreds of neuron-specific genes. We showed that REST/NRSF downregulates glutamatergic transmission in response to hyperactivity, thus contributing to neuronal homeostasis. However, whether GABAergic transmission is also implicated in the homeostatic action of REST/NRSF is unknown. Here, we show that hyperactivity-induced REST/NRSF activation, triggers a homeostatic rearrangement of GABAergic inhibition, with increased frequency of miniature inhibitory postsynaptic currents (IPSCs) and amplitude of evoked IPSCs in mouse cultured hippocampal neurons. Notably, this effect is limited to inhibitory-onto-excitatory neuron synapses, whose density increases at somatic level and decreases in dendritic regions, demonstrating a complex target- and area-selectivity. The upscaling of perisomatic inhibition was occluded by TrkB receptor inhibition and resulted from a coordinated and sequential activation of the Npas4 and Bdnf gene programs. On the opposite, the downscaling of dendritic inhibition was REST-dependent, but BDNF-independent. The findings highlight the central role of REST/NRSF in the complex transcriptional responses aimed at rescuing physiological levels of network activity in front of the ever-changing environment.

Spatiotemporal cytokinin response imaging and ISOPENTENYLTRANSFERASE 3 function in Medicago nodule development

Most legumes can establish a symbiotic association with soil rhizobia that trigger the development of root nodules. These nodules host the rhizobia and allow them to fix nitrogen efficiently. The perception of bacterial lipo-chitooligosaccharides (LCOs) in the epidermis initiates a signaling cascade that allows rhizobial intracellular infection in the root and de-differentiation and activation of cell division that gives rise to the nodule. Thus, nodule organogenesis and rhizobial infection need to be coupled in space and time for successful nodulation. The plant hormone cytokinin (CK) contributes to the coordination of this process, acting as an essential positive regulator of nodule organogenesis. However, the temporal regulation of tissue-specific CK signaling and biosynthesis in response to LCOs or Sinorhizobium meliloti inoculation in Medicago truncatula remains poorly understood. In this study, using a fluorescence-based CK sensor (pTCSn::nls:tGFP), we performed a high-resolution tissue-specific temporal characterization of the sequential activation of CK response during root infection and nodule development in M. truncatula after inoculation with S. meliloti. Loss-of-function mutants of the CK-biosynthetic gene ISOPENTENYLTRANSFERASE 3 (IPT3) showed impairment of nodulation, suggesting that IPT3 is required for nodule development in M. truncatula. Simultaneous live imaging of pIPT3::nls:tdTOMATO and the CK sensor showed that IPT3 induction in the pericycle at the base of nodule primordium contributes to CK biosynthesis, which in turn promotes expression of positive regulators of nodule organogenesis in M. truncatula.

Glutathione peroxidase-1 regulates ASK1-dependent apoptosis via interaction with TRAF2 in RIPK3-negative cancer cells

Glutathione peroxidase (GPx) is a selenocysteine-containing peroxidase enzyme that defends mammalian cells against oxidative stress, but the role of GPx signaling is poorly characterized. Here, we show that GPx type 1 (GPx1) plays a key regulatory role in the apoptosis signaling pathway. The absence of GPx1 augmented TNF-α-induced apoptosis in various RIPK3-negative cancer cells by markedly elevating the level of cytosolic H2O2, which is derived from mitochondria. At the molecular level, the absence of GPx1 led to the strengthened sequential activation of sustained JNK and caspase-8 expression. Two signaling mechanisms are involved in the GPx1-dependent regulation of the apoptosis pathway: (1) GPx1 regulates the level of cytosolic H2O2 that oxidizes the redox protein thioredoxin 1, blocking ASK1 activation, and (2) GPx1 interacts with TRAF2 and interferes with the formation of the active ASK1 complex. Inducible knockdown of GPx1 expression impaired the tumorigenic growth of MDA-MB-231 cells (>70% reduction, P = 0.0034) implanted in mice by promoting apoptosis in vivo. Overall, this study reveals the apoptosis-related signaling function of a GPx family enzyme highly conserved in aerobic organisms.

REST/NRSF drives homeostatic plasticity of inhibitory synapses in a target-dependent fashion

ABSTRACTThe repressor-element 1-silencing transcription/neuron-restrictive silencer factor (REST/NRSF) controls hundreds of neuron specific genes. We showed that REST/NRSF downregulates glutamatergic transmission in response to hyperactivity, thus contributing to neuronal homeostasis. However, whether GABAergic transmission is also implicated in the homeostatic action of REST/NRSF is unknown. Here, we show that hyperactivity-induced REST/NRSF activation triggers a homeostatic enhancement of GABAergic inhibition, with increased frequency of miniature inhibitory postsynaptic currents (IPSCs) and amplitude of evoked IPSCs. Notably, this effect was only observed at inhibitory-onto-excitatory neuron synapses, whose density increased at perisomatic sites, demonstrating a strict target-selectivity. These effects were occluded by TrkB receptor inhibition and resulted from a coordinated and sequential activation of the Npas4 and BDNF gene programs. The findings highlight the central role of REST/NRSF in the complex transcriptional responses aimed at preserving physiological levels of neuronal activity in front of the ever-changing environment.Impact StatementThis work elucidates the mechanisms by which the transcriptional regulator REST/NRSF selectively upregulates GABAergic transmission onto excitatory neurons in response to hyperactivity to rescue neuronal homeostasis.