The effect of the nitrification inhibitor dicyandiamide (DCD) on herbage production when applied at different times and rates in the autumn and winter

The high rate of urine excreted during animal grazing in late autumn provides a source of nitrogen (N) to the growing sward and also provides the potential for losses of N over the winter months. This study was established to evaluate the potential of applying a nitrification inhibitor, dicyandiamide (DCD), to urine patches to increase N use efficiency in grassland. Four simulated grazing plot experiments were undertaken across two experimental sites, one a free-draining acid brown earth (Experiments 1 and 3) and the other a moderate to heavy brown earth soil (Experiments 2 and 4). Experiments 1 and 2 received no fertiliser N application, and Experiments 3 and 4 received a split application of 350 kg N fertiliser ha−1 year−1. The effect of applying the nitrification inhibitor dicyandiamide (DCD) at 5 or 10 kg DCD ha−1 in autumn and winter to plots receiving synthetic urine or zero urine on spring and annual herbage production was examined in all experiments. The application of DCD did not increase spring herbage production in any of the experiments. Over the two years, the application of 5 or 10 kg DCD ha−1 increased annual herbage production in Experiment 1 when applied to October and November deposited urine patches. Urine application increased herbage production in spring and annually in Experiments 1 and 2, and increased herbage crude protein content and herbage N uptake in all experiments. The application of urine increased soil ammonium and TON content in the 0–100 mm horizon at both sites. The application of 10 kg DCD ha−1 reduced surplus N in Experiment 1 when applied to October and November deposited urine. Overall the effects of DCD on herbage production, surplus N and other parameters in this study were not consistent

KIF1D is a fast non-processive kinesin that demonstrates novel K-loop-dependent mechanochemistry

The KIF1 subfamily members are monomeric and contain a number of amino acid inserts in surface loops. A particularly striking insertion of several lysine/arginine residues occurs in L12 and is called the K-loop. Two recent studies have employed both kinetic and single-molecule methods to investigate KIF1 motor properties and have produced very different conclusions about how these motors generate motility. Here we show that a hitherto unstudied member of this group, KIF1D, is not chemically processive and drives fast motility despite demonstrating a slow ATPase. The K-loop of KIF1D was analysed by deletion and insertion mutagenesis coupled with characterization by steady state and transient kinetics. Together, the results indicate that the K-loop not only increases the affinity of the motor for the MT, but crucially also inhibits its subsequent isomerization from weak to strong binding, with coupled ADP release. By stabilizing the weak binding, the K-loop establishes a pool of motors primed to undergo their power stroke

Oligodendrocyte development and differentiation in the rumpshaker mutation

The jimpy rumpshaker (jprsh) mutation is an amino acid substitution in exon 4 (Ile186[RIGHTWARDS ARROW]Thr) of the proteolipid protein (PLP) gene on the X chromosome. Affected mice show moderate hypomyelination of the central nervous system (CNS) with increased numbers of oligodendrocytes in the white matter of the spinal cord, a feature distinguishing them from other PLP mutations such as jp, in which premature cell death occurs with reduced numbers of oligodendrocytes. Myelin sheaths of jprsh immunostain for myelin basic protein (MBP) and DM-20, but very few contain PLP. This study examines the differentiation of oligodendrocytes cultured from the spinal cords of young mutant and wild type mice using various surface and cytoplasmic antigenic markers to define the stage of development. The majority of oligodendrocytes from mutant mice progress normally to express MBP; approximately 30%, relative to wild type, contain DM-20 at the in vivo age of 16 days, but very few immunostain for PLP or the O10 and O11 markers. The morphology of mutant cells in respect to membrane sheets and processes appears similar to normal. The jprsh oligodendrocyte is, therefore, characterized by a failure to express the markers indicative of the most mature cell; however, it is probably able to achieve a normal period of survival. These data, taken in conjunction with previous results, suggest that the PLP gene has at least two functions; one, probably involving PLP, is concerned with a structural role in normal myelin compaction; the other, perhaps related to DM-20 (or another lower molecular weight proteolipid), is essential for cell survival. The mutation in jprsh at residue 186 suggests that this region, which is common to PLP and DM-20, is not critical for this latter function

Uncoupling of neuroinflammation from axonal degeneration in mice lacking the myelin protein tetraspanin-2

Deficiency of the major constituent of central nervous system (CNS) myelin, proteolipid protein (PLP), causes axonal pathology in spastic paraplegia type-2 patients and in Plp1null-mice but is compatible with almost normal myelination. These observations led us to speculate that PLP's role in myelination may be partly compensated for by other tetraspan proteins. Here, we demonstrate that the abundance of the structurally related tetraspanin-2 (TSPAN2) is highly increased in CNS myelin of Plp1null-mice. Unexpectedly, Tspan2null-mutant mice generated by homologous recombination in embryonic stem cells displayed low-grade activation of astrocytes and microglia in white matter tracts while they were fully myelinated and showed no signs of axonal degeneration. To determine overlapping functions of TSPAN2 and PLP, Tspan2null*Plp1null double-mutant mice were generated. Strikingly, the activation of astrocytes and microglia was strongly enhanced in Tspan2null*Plp1null double-mutants compared with either single-mutant, but the levels of dysmyelination and axonal degeneration were not increased. In this model, glial activation is thus unlikely to be caused by axonal pathology, and vice versa does not potentiate axonal degeneration. Our results support the concept that multiple myelin proteins have distinct roles in the long-term preservation of a healthy CNS, rather than in myelination per se

Rapid disruption of axon-glial integrity in response to mild cerebral hypoperfusion

Myelinated axons have a distinct protein architecture essential for action potential propagation, neuronal communication, and maintaining cognitive function. Damage to myelinated axons, associated with cerebral hypoperfusion, contributes to age-related cognitive decline. We sought to determine early alterations in the protein architecture of myelinated axons and potential mechanisms after hypoperfusion. Using a mouse model of hypoperfusion, we assessed changes in proteins critical to the maintenance of paranodes, nodes of Ranvier, axon–glial integrity, axons, and myelin by confocal laser scanning microscopy. As early as 3 d after hypoperfusion, the paranodal septate-like junctions were damaged. This was marked by a progressive reduction of paranodal Neurofascin signal and a loss of septate-like junctions. Concurrent with paranodal disruption, there was a significant increase in nodal length, identified by Nav1.6 staining, with hypoperfusion. Disruption of axon–glial integrity was also determined after hypoperfusion by changes in the spatial distribution of myelin-associated glycoprotein staining. These nodal/paranodal changes were more pronounced after 1 month of hypoperfusion. In contrast, the nodal anchoring proteins AnkyrinG and Neurofascin 186 were unchanged and there were no overt changes in axonal and myelin integrity with hypoperfusion. A microarray analysis of white matter samples indicated that there were significant alterations in 129 genes. Subsequent analysis indicated alterations in biological pathways, including inflammatory responses, cytokine-cytokine receptor interactions, blood vessel development, and cell proliferation processes. Our results demonstrate that hypoperfusion leads to a rapid disruption of key proteins critical to the stability of the axon–glial connection that is mediated by a diversity of molecular events