Previous work has shown that introduction of hexafluoroacetylacetone (Facac) units as nonstructural ligands for the zirconia-like nodes of the eight-connected metal–organic framework (MOF), NU-1000, ...greatly alters the selectivity of node-supported oxy-nickel clusters for ethylene dimerization vs oligomerization. Here we explore a related concept: tuning of support/catalyst interactions, and therefore, catalyst activity, via parallel installation of organic modifiers on the support itself. As modifiers we focused on para-substituted benzoates (R-BA–; R = −NH2, −OCH3, −CH3, −H, −F, and −NO2) where the substituents were chosen to present similar steric demand, but varying electron-donating or electron-withdrawing properties. R-benzoate-engendered shifts in the node-based aqua O–H stretching frequency for NU-1000, as measured by DRIFTS (diffuse-reflectance infrared Fourier-transform spectroscopy), together with systematic shifts in Ni 2p peak energies, as measured by X-ray photoelectron spectroscopy, show that the electronic properties of the support can be modulated. The vibrational and electronic peak shifts correlate with the putative electron-withdrawing vs electron-donating strength of the para-substituted benzoate modifiers. Subsequent installation of node-supported, oxy-Ni(II) clusters for ethylene hydrogenation yield a compelling correlation between log (catalyst turnover frequency) and the electron donating or withdrawing character of the substituent of the benzoate units. Single crystal X-ray diffraction measurements reveal that each organic modifier makes use of only one of two available carboxylate oxygens to accomplish grafting. The remaining oxygen atom is, in principle, well positioned to coordinate directly to an installed Ni(II) ion. We postulate that the unanticipated direct coordination of the catalyst by the node-modifier (rather than indirect modifier-based tuning of support(node)/catalyst electronic interactions) is the primary source of the observed systematic tuning of hydrogenation activity. We suggest, however, that regardless of mechanism for communication with active-sites of MOF-supported catalysts, intentional elaboration of nodes via grafted, nonstructural organic species could prove to be a valuable general strategy for fine-tuning supported-catalyst activity and/or selectivity.
High-strength magnetic fields were used to align collagen gel formed into 4-mm-diameter rods during the self-assembly of type I collagen monomers into fibrils. We developed an in vitro assay to study ...neurite elongation into the magnetically aligned collagen gel rods from dorsal root ganglia (DRG) explants placed onto one end of the rods. The depth of neurite elongation from chick embryo DRG neurons into these rods was found to be substantially greater than that observed in controls and increased with an increase in magnetic field strength, as did the collagen gel rod birefringence, indicative of collagen fibril alignment along the rod axis. Moreover, the axial bias of neurite elongation became more pronounced with an increase in magnetic field strength, presumably due to a contact guidance response of growth cones at the neurite tips. Coinvasion of Schwann cells from neonatal rat DRG was also studied in these assays using double immunolabeling. In the absence of serum, Schwann cells were highly associated with, and often trailed, elongating neurites. In the presence of serum, Schwann cells showed significantly higher rates of invasion and formed axially aligned chords reminiscent of bands of Büngner. These results may translate into an improved method of entubulation repair of transected peripheral nerves by directing and stimulating axonal growth through a tube filled with magnetically aligned collagen gel.
Neurite outgrowth from chick dorsal root ganglia entrapped in isotropic and magnetically aligned fibrin gels was studied, and the dependence on the diameter of the fibrin fibrils was characterized. ...The fibrin fibril diameter was varied, as inferred from turbidity measurements, by using different Ca
2+ concentrations in the fibrin-forming solution, but this variation was accomplished without affecting the degree of magnetic-induced alignment, as directly visualized in fluorescently spiked gels. Magnetically aligned fibrin gels possessing different fibril diameters but similar alignment resulted in drastic changes in the contact guidance response of neurites, with no response in gels formed in 1.2
m
m Ca
2+ (having smaller fibril diameter, ca. 150
nm), but a strong response in gels formed in 12 and 30
m
m Ca
2+ (having larger fibril diameter, ca. 510
nm) with an attendant two-fold increase in neurite length. These changes are attributed to variation of the mechano-structural properties of the network of aligned fibrils as the fibril diameter is varied.
Receptors of the integrin family are expressed by every cell type and are the primary means by which cells interact with the extracellular matrix. The control of integrin expression affects a wide ...range of developmental and cellular processes, including the regulation of gene expression, cell adhesion, cell morphogenesis and cell migration. Here we show that the concentration of substratum-bound ligand (laminin) post-translationally regulates the amount of receptor (α6β1 integrin) expressed on the surface of sensory neurons. When ligand availability is low, surface amounts of receptor increase, whereas integrin RNA and total integrin protein decrease. Ligand concentration determines surface levels of integrin by altering the rate at which receptor is removed from the cell surface. Furthermore, increased expression of integrin at the cell surface is associated with increased neuronal cell adhesion and neurite outgrowth. These results indicate that integrin regulation maintains neuronal growth-cone motility over a broad range of ligand concentrations, allowing axons to invade different tissues during development and regeneration.
•Precision feeding allows pigs to be fed with diets tailored daily to requirements.•Pigs fed with daily tailored diets retain 9% more N than conventionally fed pigs.•Actual nutritional models might ...overestimate requirements of heavy pigs.•Adjusts in dietary protein and AA may decrease environmental burden.•Precision feeding application requires better understating of metabolic responses.
Optimal amino acid ratios for pigs have been established for conventional phase feeding systems, but these ratios may differ for precision feeding systems. Our objective was to assess the impact of different dietary Thr inclusion levels (70, 85, 100, 115, or 130% of the estimated ideal 0.65 Thr:Lys ratio) on growth performance, plasma biochemical parameters, and splanchnic and muscle AA composition in pigs raised in a conventional group phase feeding (GPF) system and in an individual precision feeding (IPF) system. A total of 110 finishing pigs (110 ± 7.02 kg initial body weight; 11 pigs per treatment) were housed in the same room for 21 d. Pigs were randomly assigned to a 2 × 5 factorial arrangement and fed using automatic feeders. Individual pigs were considered the experimental units. Five pigs per treatment were slaughtered at the end of the trial. The gain:feed ratio was not affected by feeding system, but there was a quadratic effect of Thr inclusion rate (P < 0.05). Lysine intake was 16% greater and Thr intake was 15% greater for the GPF pigs than for the IPF pigs (P < 0.05). Protein deposition (g/d) was not affected by any treatment. Protein deposition in daily gain was affected by the interaction between Thr inclusion rate and feeding system, with a quadratic (P < 0.05) effect for the GPF pigs and a cubic (P < 0.10) effect for the IPF pigs. The pigs in IPF consumed 14% less (P < 0.05) crude protein and excreted 17% less (P < 0.05) N than the GPF pigs did. The pigs in IPF retained 9% more (P < 0.05) N than the GPF pigs. Plasma urea values were 9% higher (P < 0.05) in GPF than those in IPF. The gamma-glutamyl transferase enzyme decreased (P < 0.05) in a quadratic manner within IPF but increased (P < 0.05) in a quadratic manner within GPF. In the IPF systems, the average concentration of albumin and C-reactive protein tended (P < 0.10) to be 2 and 22% lower, respectively, than in GPF. Changes in amino acid concentrations occurred mainly in the liver of the IPF pigs. The pigs in IPF had higher (P < 0.05) concentrations of collagen in the longissimus dorsi than the pigs in GPF. Lastly, IPF allowed standardized ileal digestible Lys and Thr intakes to decrease by 16 and 15%, respectively, without differences in average daily gain and gain:feed ratio in comparison with GPF.
The mechanisms by which neurotrophins regulate growth cone motility are unclear. We investigated the role of the p75 neurotrophin receptor (p75NTR) in mediating neurotrophin-induced increases in ...filopodial length. Our data demonstrate that neurotrophin binding to p75NTR is necessary and sufficient to regulate filopodial dynamics. Furthermore, retinal and dorsal root ganglion growth cones from p75 mutant mice are insensitive to neurotrophins but display enhanced filopodial lengths comparable with neurotrophin-treated wild-type growth cones. This suggests unoccupied p75NTR negatively regulates filopodia length. Furthermore, p75NTR regulates RhoA activity to mediate filopodial dynamics. Constitutively active RhoA blocks neurotrophin-induced increases in filopodial length, whereas inhibition of RhoA enhances filopodial lengths, similar to neurotrophin treatment. BDNF treatment of retinal neurons results in reduced RhoA activity. Furthermore, p75 mutant neurons display reduced levels of activated RhoA compared with wild-type counterparts, consistent with the enhanced filopodial lengths observed on mutant growth cones. These observations suggest that neurotrophins regulate filopodial dynamics by depressing the activation of RhoA that occurs through p75NTR signaling.
Neurotrophins and semaphorin 3A are present along pathways and in targets of developing axons of dorsal root ganglion (DRG) sensory neurons. Growth cones of sensory axons are probably regulated by ...interaction of cytoplasmic signaling triggered coincidentally by both types of guidance molecules. We investigated the in vitro interactions of neurotrophins and semaphorin 3A (Sema3A) in modulating growth cone behaviors of axons extended from DRGs of embryonic day 7 chick embryos. Growth cones of DRGs raised in media containing 10(-9) m NGF or BDNF were more resistant to Sema3A-induced growth cone collapse than when DRGs were raised in 10(-11) m NGF. After overnight culture in 10(-11) m NGF, a 1 hr treatment with 10(-9) m NGF or BDNF was sufficient to increase growth cone resistance to Sema3A-induced collapse. This neurotrophin-mediated decrease in the collapse response of DRG growth cones was not associated with reduced expression on growth cones of the Sema3A-binding protein neuropilin-1. A series of pharmacological studies followed. Phosphatidylinositol 3 kinase activity is not required for these effects of NGF. The effects of inhibitors and activators of protein kinase A (PKA) indicate that PKA activity is involved in NGF modulation of Sema3A-induced growth cone collapse. The effects of inhibitors and activators of PKG indicate that PKG activity is involved in Sema3A-induced growth cone collapse. The effects of inhibitors also indicate that Rho-kinase activity is involved in Sema3A-induced growth cone collapse. These results are consistent with the idea that growth cone responses to an individual guidance cue depend on coincident signaling by other guidance cues and by other regulatory pathways.
•Small ruminants may suffer from marine lipid-induced milk fat depression (MFD).•The involvement of the ruminal t10-shift in this MFD remained uncertain.•This study summarized the relationship ...between the t10-shift and MFD in dairy ewes.•Inverse relationships between milk fat traits and t10-shift were found.•The t10-shift would not be a major explanation of marine lipid-induced MFD in sheep.
The causative relationship between ruminal biohydrogenation alterations known as the trans-10 shift and marine lipid-induced milk fat depression (MFD) has been questioned in dairy ewes, but the large intra- and inter-experiment differences in the levels of trans-10 shift indicators precludes firm conclusions. This meta-analysis was conducted to quantify the relationship between trans-10 shift milk indicators i.e., trans-10,cis-12 conjugated linoleic acid (CLA), trans-10 18:1 or trans-10:trans-11 18:1 ratio and lactation performance, mainly milk fat traits, in Assaf dairy ewes. A database comprising of 17 experiments including 50 dietary treatments was compiled. The diets were grouped into 2 dietary conditions: (1) non-MFD condition, which included 14 diets supplemented with plant oils and tannins that modified the milk fatty acid profile without lowering milk fat concentration and yield, and 12 respective control diets, and (2) MFD condition, which included 15 diets supplemented with marine lipids that induced the low fat-milk syndrome, and 9 respective control diets. The overall levels of milk trans-10 shift indicators did not differ between dietary conditions, but significant increments were found in the supplemented diets relative to their respective controls. A similar linear and negative (slope: −7.28 ± 2.816) relationship between milk fat concentration and trans-10,cis-12 CLA was found in both dietary conditions. However, the quadratic negative response of milk fat content to trans-10 18:1 concentration was greater in MFD than in non-MFD conditions. In the two dietary conditions, the relationship between milk trans-10,cis-12 CLA or trans-10 18:1 and de novo fatty acid concentration in milk was negative, whereas the relationship with preformed fatty acid proportion was positive. The magnitude of changes in both milk fatty acid groups in response to changes in these trans-10 shift indicators were greater in non-MFD compared with MFD conditions. Milk fat yield and trans-10 shift indicators were only negatively related in ewes that were fed marine lipid supplements, because reductions in de novo fatty acid yield with increased shift indicator levels were not counteracted by concomitant increments in preformed fatty acid secretion. The best-fit (lower root mean squared error, higher R2 and no prediction biases) equations of milk fat or major milk fatty acid groups, as concentration or yield, were based on milk trans-10 18:1 concentration. In conclusion, different responses between the two conditions to similar shift indicator levels support that the trans-10 shift would not be a major factor explaining the diet-induced low-fat milk syndrome in dairy ewes.
1. This study assessed the effect of limestone particle size and microbial phytase incorporation on the fate of phosphorus (P) and calcium (Ca) along the gastrointestinal tract in 72 laying hens.2. ...Four experimental diets were formulated according to a 2 × 2 factorial arrangement to evaluate the effect of two coarse limestone (CL) inclusion. This included a mix (MIX) of 75% CL (2 - 4 mm) and 25% fine particles (FL, <0.5 mm) or 100% FL, in two different basal diets formulated without (MIX0 and FL0) or with 300 FTU of microbial phytase/kg (MIX300 and FL300).3. Contents of the crop, gizzard, duodenum, jejunum and ileum were collected to determine the mean retention time (MRT) of dry matter (DM), the recovery rate of Ca and P in each segment of the gastrointestinal tract and the apparent fractional digestibility coefficient (AD) of Ca and P in each intestinal segment.4. In hens fed FL, microbial phytase decreased the MRT of DM along the intestine (
< 0.05). In the crop and the gizzard, Ca recovery increased with MIX incorporation to a greater extent in hens fed without microbial phytase (
< 0.05). The mixed particle size incorporation decreased absorption kinetics of Ca in hens fed microbial phytase. The AD of P and the absorption kinetics of P were significantly decreased in hens receiving FL300, probably due to complex formation between Ca and phytic acid.5. This study showed that coarse limestone particles incorporation improved mineral utilisation along the digestive tract.
The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the ...appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 micro(m) through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead-axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead-axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca2+ fluctuations. These findings implicate neurotrophins as local cues that directly stimulate the formation of collateral axon branches.
PDF
