22 research outputs found
Strongly Anisotropic Spin and Orbital Rashba Effect at a Tellurium - Noble Metal Interface
We study the interplay of lattice, spin and orbital degrees of freedom in a
two-dimensional model system: a flat square lattice of Te atoms on a Au(100)
surface. The atomic structure of the Te monolayer is determined by scanning
tunneling microscopy (STM) and quantitative low-energy electron diffraction
(LEED-IV). Using spin- and angle-resolved photoelectron spectroscopy (ARPES)
and density functional theory (DFT), we observe a Te-Au interface state with
highly anisotropic Rashba-type spin-orbit splitting at the X point of the
Brillouin zone. Based on a profound symmetry and tight-binding analysis, we
show how in-plane square lattice symmetry and broken inversion symmetry at the
Te-Au interface together enforce a remarkably anisotropic orbital Rashba effect
which strongly modulates the spin splitting.Comment: 7 pages, 5 figure
Editing the genome of chicken primordial germ cells to introduce alleles and study gene function
With continuing advances in genome sequencing technology, the chicken genome
assembly is now better annotated with improved accuracy to the level of single
nucleotide polymorphisms. Additionally, the genomes of other birds such as the duck,
turkey and zebra finch have now been sequenced. A great opportunity exists in avian
biology to use genome editing technology to introduce small and defined sequence
changes to create specific haplotypes in chicken to investigate gene regulatory
function, and also perform rapid and seamless transfer of specific alleles between
chicken breeds. The methods for performing such precise genome editing are well
established for mammalian species but are not readily applicable in birds due to
evolutionary differences in reproductive biology.
A significant leap forward to address this challenge in avian biology was the
development of long-term culture methods for chicken primordial germ cells (PGCs).
PGCs present a cell line in which to perform targeted genetic manipulations that will
be heritable. Chicken PGCs have been successfully targeted to generate genetically
modified chickens. However, genome editing to introduce small and defined sequence
changes has not been demonstrated in any avian species. To address this deficit, the
application of CRISPR/Cas9 and short oligonucleotide donors in chicken PGCs for
performing small and defined sequence changes was investigated in this thesis.
Specifically, homology-directed DNA repair (HDR) using oligonucleotide donors
along with wild-type CRISPR/Cas9 (SpCas9-WT) or high fidelity CRISPR/Cas9
(SpCas9-HF1) was investigated in cultured chicken PGCs. The results obtained
showed that small sequences changes ranging from a single to a few nucleotides could
be precisely edited in many loci in chicken PGCs. In comparison to SpCas9-WT,
SpCas9-HF1 increased the frequency of biallelic and single allele editing to generate
specific homozygous and heterozygous genotypes. This finding demonstrates the
utility of high fidelity CRISPR/Cas9 variants for performing sequence editing with
high efficiency in PGCs.
Since PGCs can be converted into pluripotent stem cells that can potentially
differentiate into many cell types from the three germ layers, genome editing of PGCs
can, therefore, be used to generate PGC-derived avian cell types with defined genetic
alterations to investigate the host-pathogen interactions of infectious avian diseases.
To investigate this possibility, the chicken ANP32A gene was investigated as a target
for genetic resistance to avian influenza virus in PGC-derived chicken cell lines.
Targeted modification of ANP32A was performed to generate clonal lines of genome-edited
PGCs. Avian influenza minigenome replication assays were subsequently
performed in the ANP32A-mutant PGC-derived cell lines. The results verified that
ANP32A function is crucial for the function of both avian virus polymerase and
human-adapted virus polymerase in chicken cells. Importantly, an asparagine to
isoleucine mutation at position 129 (N129I) in chicken ANP32A failed to support
avian influenza polymerase function. This genetic change can be introduced into
chickens and validated in virological studies. Importantly, the results of my
investigation demonstrate the potential to use genome editing of PGCs as an approach
to generate many types of unique cell models for the study of avian biology.
Genome editing of PGCs may also be applied to unravel the genes that control the
development of the avian germ cell lineage. In the mouse, gene targeting has been
extensively applied to generate loss-of-function mouse models to use the reverse
genetics approach to identify key genes that regulate the migration of specified PGCs
to the genital ridges. Avian PGCs express similar cytokine receptors as their
mammalian counterparts. However, the factors guiding the migration of avian PGCs
are largely unknown. To address this, CRISPR/Cas9 was used in this thesis to generate
clonal lines of chicken PGCs with loss-of-function deletions in the CXCR4 and c-Kit
genes which have been implicated in controlling mouse PGC migration. The results
showed that CXCR4-deficient PGCs are absent from the gonads whereas c-Kit-deficient
PGCs colonise the developing gonads in reduced numbers and are
significantly reduced or absent from older stages. This finding shows a conserved role
for CXCR4 and c-Kit signalling in chicken PGC development. Importantly, other
genes suspected to be involved in controlling the development of avian germ cells can
be investigated using this approach to increase our understanding of avian reproductive
biology.
Finally, the methods developed in this thesis for editing of the chicken genome may
be applied in other avian species once culture methods for the PGCs from these species
are develope
Strongly anisotropic spin and orbital Rashba effect at a tellurium – noble metal interface
We study the interplay of lattice, spin, and orbital degrees of freedom in a two-dimensional model system: a flat square lattice of Te atoms on a Au(100) surface. The atomic structure of the Te monolayer is determined by scanning tunneling microscopy and quantitative low-energy electron diffraction. Using spin- and angle-resolved photoelectron spectroscopy and density functional theory, we observe a Te-Au interface state with highly anisotropic Rashba-type spin-orbit splitting at the X point of the Brillouin zone. Based on a profound symmetry and tight-binding analysis, we show how in-plane square lattice symmetry and broken inversion symmetry at the Te-Au interface together enforce a remarkably anisotropic orbital Rashba effect which strongly modulates the spin splitting
Hypoglycin A Content in Blood and Urine Discriminates Horses with Atypical Myopathy from Clinically Normal Horses Grazing on the Same Pasture
<div><p>Hypoglycin A (HGA) in seeds of <i>Acer spp</i>. is suspected to cause seasonal pasture myopathy in North America and equine atypical myopathy (AM) in Europe, fatal diseases in horses on pasture. In previous studies, this suspicion was substantiated by the correlation of seed HGA content with the concentrations of toxic metabolites in urine and serum (MCPA-conjugates) of affected horses. However, seed sampling was conducted after rather than during an outbreak of the disease. The aim of this study was to further confirm the causality between HGA occurrence and disease outbreak by seed sampling during an outbreak and the determination of i) HGA in seeds and of ii) HGA and MCPA-conjugates in urine and serum of diseased horses. Furthermore, cograzing healthy horses, which were present on AM affected pastures, were also investigated. AM-pastures in Germany were visited to identify seeds of <i>Acer pseudoplatanus</i> and serum (n = 8) as well as urine (n = 6) from a total of 16 diseased horses were analyzed for amino acid composition by LC-ESI-MS/MS, with a special focus on the content of HGA. Additionally, the content of its toxic metabolite was measured in its conjugated form in body fluids (UPLC-MS/MS). The seeds contained 1.7–319.8 μg HGA/g seed. The content of HGA in serum of affected horses ranged from 387.8–8493.8 μg/L (controls < 10 μg/L), and in urine from 143.8–926.4 μg/L (controls < 10 μg/L), respectively. Healthy cograzing horses on AM-pastures showed higher serum (108.8 ± 83.76 μg/L) and urine concentrations (26.9 ± 7.39 μg/L) compared to control horses, but lower concentrations compared to diseased horses. The range of MCPA-carnitine and creatinine concentrations found in diseased horses in serum and urine were 0.17–0.65 mmol/L (controls < 0.01), and 0.34–2.05 μmol/mmoL (controls < 0.001), respectively. MCPA-glycine levels in urine of cograzing horses were higher compared to controls. Thus, the causal link between HGA intoxication and disease outbreak could be further substantiated, and the early detection of HGA in cograzing horses, which are clinically normal, might be a promising step in prophylaxis.</p></div
Specific characteristics of AM-affected and cograzing horses dedicated to the individual AM-pasture.
<p>TN = total number of horses on individual pasture; <sup>1</sup> in hrs/d, *additional food stuffs (hay, concentrate); AH = affected horses, CG = cograzing horses: the denomination is made up of the letter of pasture (A-L) and the number of affected or cograzing horses on this pasture; WB = Warmblood, GRP = German Riding Pony, HF = haflinger; g = gelding, m = male, s = stallion; **survived, affect date 17<sup>th</sup> Nov 2013, ***not available.</p
Pasture B.
<p>Numerous seeds found on pasture where the closest sycamore maple tree was 50 meters away from the pasture.</p
Hypoglycin A concentration in seeds of <i>Acer pseudoplatanus</i> collected from affected pastures detected by LC-ESI-MS/MS analysis.
<p>pasture B,C,E,F sampled in 2013; pasture G,H,J,K,L sampled in 2014.</p
Sustainability as a Driver in Forestry‐Related Services
Rising environmental consciousness has shifted the focus of small-scale forestry away from productive functions towards more diversified ownership objectives. From transition management perspective, we analyze the role of private sector voluntary sustainability initiatives as a system driver in forestry, and review research on the role of sustainability in forestry-related service markets. The focus is on the view of small-scale service-oriented businesses, and by drawing experiences from the Nordic context. Based on the literature review, sustainability is gaining deeper level interest and active engagement among small scale forest owners due to, perhaps first and foremost, increasing awareness on global sustainability challenges, and the role of forests in these. A challenge remains in diffusion of the sustainability-related niche innovations. In addition, the strong environmental-economic emphasis in sustainability may lead to the undervaluing the potential of some socially driven forest ecosystem services. The effectiveness of new methods, such as framing as a tool to nudge family owners towards more sustainable forestry practices, provides avenues for future experimentation and research.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Organisation and Governanc