228 research outputs found
P02.165. A comparative effectiveness trial of high-quality vitamin D3 nutritional supplements to replete serum vitamin D
Microarray analysis of E9.5 reduced folate carrier (RFC1; Slc19a1) knockout embryos reveals altered expression of genes in the cubilin-megalin multiligand endocytic receptor complex
<p>Abstract</p> <p>Background</p> <p>The reduced folate carrier (<it>RFC1</it>) is an integral membrane protein and facilitative anion exchanger that mediates delivery of 5-methyltetrahydrofolate into mammalian cells. Adequate maternal-fetal transport of folate is necessary for normal embryogenesis. Targeted inactivation of the murine <it>RFC1 </it>gene results in post-implantation embryolethality, but daily folic acid supplementation of pregnant dams prolongs survival of homozygous embryos until mid-gestation. At E10.5 <it>RFC1</it><sup>-/- </sup>embryos are developmentally delayed relative to wildtype littermates, have multiple malformations, including neural tube defects, and die due to failure of chorioallantoic fusion. The mesoderm is sparse and disorganized, and there is a marked absence of erythrocytes in yolk sac blood islands. The identification of alterations in gene expression and signaling pathways involved in the observed dysmorphology following inactivation of RFC1-mediated folate transport are the focus of this investigation.</p> <p>Results</p> <p>Affymetrix microarray analysis of the relative gene expression profiles in whole E9.5 <it>RFC1</it><sup>-/- </sup>vs. <it>RFC1</it><sup>+/+ </sup>embryos identified 200 known genes that were differentially expressed. Major ontology groups included transcription factors (13.04%), and genes involved in transport functions (ion, lipid, carbohydrate) (11.37%). Genes that code for receptors, ligands and interacting proteins in the cubilin-megalin multiligand endocytic receptor complex accounted for 9.36% of the total, followed closely by several genes involved in hematopoiesis (8.03%). The most highly significant gene network identified by Ingenuity™ Pathway analysis included 12 genes in the cubilin-megalin multiligand endocytic receptor complex. Altered expression of these genes was validated by quantitative RT-PCR, and immunohistochemical analysis demonstrated that megalin protein expression disappeared from the visceral yolk sac of <it>RFC1</it><sup>-/- </sup>embryos, while cubilin protein was widely misexpressed.</p> <p>Conclusion</p> <p>Inactivation of <it>RFC1 </it>impacts the expression of several ligands and interacting proteins in the cubilin-amnionless-megalin complex that are involved in the maternal-fetal transport of folate and other nutrients, lipids and morphogens such as sonic hedgehog (Shh) and retinoids that play critical roles in normal embryogenesis.</p
On the next-to-leading-order correction to the effective action in N=2 gauge theories
I attempt to analyse the next-to-leading-order non-holomorphic contribution
to the Wilsonian low-energy effective action in the four-dimensional N=2 gauge
theories with matter, from the manifestly N=2 supersymmeric point of view, by
using the harmonic superspace. The perturbative one-loop correction is found to
be in agreement with the N=1 superfield calculations of de Wit, Grisaru and
Rocek. The previously unknown coefficient in front of this non-holomorphic
correction is calculated. A special attention is devoted to the N=2
superconformal gauge theories, whose one-loop non-holomorphic contribution is
likely to be exact, even non-perturbatively. This leading (one-loop)
non-holomorphic contribution to the LEEA of the N=2 superconformally invariant
gauge field theories is calculated, and it does not vanish, similarly to the
case of the N=4 super-Yang-Mills theory.Comment: 15 pages, LaTeX; changes in the abstract and in sect.
Grand Unification with Three Generations in Free Fermionic String Models
We examine the problem of constructing three generation free fermionic string
models with grand unified gauge groups. We attempt the construction of models, where is a grand unified group realized at level 1. This
structure allows those Higgs representations to appear which are necessary to
break the symmetry down to the standard model gauge group. For , we
find only models with an even number of generations. However, for we
find a number of 3 generation models.Comment: 22 pages, latex. References added to original versio
Nonperturbative Renormalization Group Equation and Beta Function in N=2 SUSY Yang-Mills
We obtain the exact beta function for SUSY Yang-Mills theory
and prove the nonperturbative Renormalization Group Equation Comment: LaTex, 10 pg. Expanded introduction, references added, to appear in
Phys. Rev. Let
A Classification of 3-Family Grand Unification in String Theory I. The SO(10) and E_6 Models
We give a classification of 3-family SO(10) and E_6 grand unification in
string theory within the framework of conformal field theory and asymmetric
orbifolds. We argue that the construction of such models in the heterotic
string theory requires certain Z_6 asymmetric orbifolds that include a Z_3
outer-automorphism, the latter yielding a level-3 current algebra for the grand
unification gauge group SO(10) or E_6. We then classify all such Z_6 asymmetric
orbifolds that result in models with a non-abelian hidden sector. All models
classified in this paper have only one adjoint (but no other higher
representation) Higgs field in the grand unified gauge group. In addition, all
of them are completely anomaly free. There are two types of such 3-family
models. The first type consists of the unique SO(10) model with SU(2) X SU(2) X
SU(2) as its hidden sector (which is not asymptotically-free at the string
scale). This SO(10) model has 4 left-handed and 1 right-handed 16s. The second
type is described by a moduli space containing 17 models (distinguished by
their massless spectra). All these models have an SU(2) hidden sector, and 5
left-handed and 2 right-handed families in the grand unified gauge group. One
of these models is the unique E_6 model with an asymptotically-free SU(2)
hidden sector. The others are SO(10) models, 8 of them with an asymptotically
free hidden sector at the string scale.Comment: 35 pages, Revtex 3.0, one eps figure (to appear in Phys. Rev. D
N=2 SYM Action as a BRST Exact Term, Topological Yang Mills and Instantons
By constructing a nilpotent extended BRST operator \bs that involves the
N=2 global supersymmetry transformations of one chirality, we show that the
standard N=2 off-shell Super Yang Mills Action can be represented as an exact
BRST term \bs \Psi, if the gauge fermion is allowed to depend on the
inverse powers of supersymmetry ghosts. By using this nonanalytical structure
of the gauge fermion (via inverse powers of supersymmetry ghosts), we give
field redefinitions in terms of composite fields of supersymmetry ghosts and
N=2 fields and we show that Witten's topological Yang Mills theory can be
obtained from the ordinary Euclidean N=2 Super Yang Mills theory directly by
using such field redefinitions. In other words, TYM theory is obtained as a
change of variables (without twisting). As a consequence it is found that
physical and topological interpretations of N=2 SYM are intertwined together
due to the requirement of analyticity of global SUSY ghosts. Moreover, when
after an instanton inspired truncation of the model is used, we show that the
given field redefinitions yield the Baulieu-Singer formulation of Topological
Yang Mills.Comment: Latex, 1+15 pages. Published versio
Realizing Higher-Level Gauge Symmetries in String Theory: New Embeddings for String GUTs
We consider the methods by which higher-level and non-simply laced gauge
symmetries can be realized in free-field heterotic string theory. We show that
all such realizations have a common underlying feature, namely a dimensional
truncation of the charge lattice, and we identify such dimensional truncations
with certain irregular embeddings of higher-level and non-simply laced gauge
groups within level-one simply-laced gauge groups. This identification allows
us to formulate a direct mapping between a given subgroup embedding, and the
sorts of GSO constraints that are necessary in order to realize the embedding
in string theory. This also allows us to determine a number of useful
constraints that generally affect string GUT model-building. For example, most
string GUT realizations of higher-level gauge symmetries G_k employ the
so-called diagonal embeddings G_k\subset G\times G \times...\times G. We find
that there exist interesting alternative embeddings by which such groups can be
realized at higher levels, and we derive a complete list of all possibilities
for the GUT groups SU(5), SU(6), SO(10), and E_6 at levels k=2,3,4 (and in some
cases up to k=7). We find that these new embeddings are always more efficient
and require less central charge than the diagonal embeddings which have
traditionally been employed. As a byproduct, we also prove that it is
impossible to realize SO(10) at levels k>4. This implies, in particular, that
free-field heterotic string models can never give a massless 126 representation
of SO(10).Comment: 69 pages, LaTeX, 5 figures (Encapsulated PostScript). Revised to
match published versio
SU(2) Yang-Mills Theory with extended Supersymmetry in a Background Magnetic Field
The vacuum structure of N=2 (and N=4) SUSY Yang-Mills theory is analyzed in
detail by considering the effective potential for constant background scalar-
magnetic fields within different approximations. We compare the one-loop
approximation with- or without instanton improved effective coupling with the
one-loop result in the dual desription. For N=2 we find that non-perturbative
monopole degrees of freedom remove the non-trivial minima present in the
(improved) one-loop potential in the strong-coupling regime. The combination of
Yang-Mills and dual desription leads to a self-consistent effective potential
over the full range of background fields.Comment: 15 pages, Revtex, 3 figures, References added, section two shortened,
some minor remarks and corrections adde
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