405 research outputs found
Insulin increases the cell number of the inner cell mass and stimulates morphological development of mouse blastocysts in vitro
Previous studies showed that insulin promotes cell proliferation and morphological development of preimplantation mouse embryos. In this report, the receptor responsible for these actions and the cell populations that are affected were investigated. Insulin's 9% stimulation of blastocyst cell number was entirely due to a 23% increase in ICM cell number with an EC50 of 0.54 pM. This and the similar degrees of stimulation of immunosurgically isolated ICMs by both physiological and supraphysiological insulin concentrations suggest that insulin receptors are present on the ICM and respond to exogenous insulin transcytosed through the TE to promote expansion of the ICM cell numbers. In morphological studies, insulin increased the number of blastocysts and decreased the number of morulae by 10% after 54 h culture from 2-cell embryos with EC50s of about 0.95 pM. The equivalence of these EC50s suggests mediation of insulin's stimulation of blastocyst formation via insulin receptors which are functionally expressed around the time of compaction at the 8-cell stage. These results support our hypothesis that insulin has an important role in the regulation of growth during preimplantation development
IGF-2 receptors are first expressed at the 2-cell stage of mouse development
A specific IGF-2 receptor antiserum was used to reveal the presence of IGF-2 receptors during preimplantation development of mice. Receptors were present on 2-, 4- and 8-cell embryos, morulae, blastocysts, and on ICMs isolated prior to staining. There was no evidence for receptors on fertilized eggs. These observations confirm reports of the expression of IGF-2 receptor mRNA as early as the 2-cell stage and refine similar observations in blastocysts to confirm expression in both the TE and ICM. A potential auto/paracrine loop is thus one of the first products of activation of the embryonic genome and is expressed constitutively through preimplantation development
The Self-Dual String and Anomalies in the M5-brane
We study the anomalies of a charge self-dual string solution in the
Coulomb branch of M5-branes. Cancellation of these anomalies allows us to
determine the anomaly of the zero-modes on the self-dual string and their
scaling with and . The dimensional reduction of the five-brane
anomalous couplings then lead to certain anomalous couplings for D-branes.Comment: 13 pages, Harvmac, refs adde
Membrane solitons in eight-dimensional hyper-Kaehler backgrounds
We derive the BPS equations satisfied by lump solitons in -dimensional
sigma models with toric 8-dimensional hyper-K\"ahler () target spaces
and check they preserve 1/2 of the supersymmetry. We show how these solitons
are realised in M theory as M2-branes wrapping holomorphic 2-cycles in the
\bE^{1,2}\times {HK}_8 background. Using the -symmetry of a probe
M2-brane in this background we determine the supersymmetry they preserve, and
note that there is a discrepancy in the fraction of supersymmetry preserved by
these solitons as viewed from the low energy effective sigma model description
of the M2-brane dynamics or the full M theory. Toric manifolds are
dual to a Hanany-Witten setup of D3-branes suspended between 5-branes. In this
picture the lumps correspond to vortices of the three dimensional or theory.Comment: 12+1 pages. LaTex. v2: Typos corrected and references adde
A bound on 6D N=1 supergravities
We prove that there are only finitely many distinct semi-simple gauge groups
and matter representations possible in consistent 6D chiral (1,0) supergravity
theories with one tensor multiplet. The proof relies only on features of the
low-energy theory; the consistency conditions we impose are that anomalies
should be cancelled by the Green-Schwarz mechanism, and that the kinetic terms
for all fields should be positive in some region of moduli space. This result
does not apply to the case of the non-chiral (1,1) supergravities, which are
not constrained by anomaly cancellation.Comment: 23 pages, no figures; two paragraphs added to the proof in Appendix A
covering the SU(2) and SU(3) case, other minor correction
Attempts to identify Cassava Brown Streak Virus in western Democratic Republic of Congo
Open Access ArticleRoot necrosis similar to those of the cassava brown streak disease (CBSD) were observed on cassava in western provinces of the Democratic Republic of Congo (DR.Congo) in the early 2000âs. However molecular laboratory diagnosis were not able to detect any causative agent responsible for the attacks, hence, the disease related to these symptoms was named CBSD-like disease.
In order to assess the distribution and the incidence of the CBSD-like disease, surveys were carried out in four western provinces, comprising, Kwango and Kwilu, Sud Ubangi, Kinshasa and Kongo Central. CBSD-like disease was observed in all surveyed provinces on the basis of root symptoms because foliar symptoms were different to those of the documented cases of CBSD in other parts of east Africa. CBSD-like disease incidence was high in Kongo Central and Sud Ubangi, exceeding an average of 50 %, but low in Kwango and Kwilu (32.8%) and in Kinshasa (19.1%).
During the surveys, cassava leaf samples were collected for lab identification of the causal agent. PCR diagnosis was done on these samples using primers specific for the two known CBSVs. All samples tested negative with no amplification of DNA fragments of the correct size. Thus, further analysis on the causative organism is needed using Next Generation Sequencing (NGS) approaches. NGS approaches will help also to identify the causative organism in other Central Africa countries (Angola, Congo-Brazzaville and Gabon) where such cassava root necrosis have been reported or are suspected
Spin dependent D-brane interactions and scattering amplitudes in matrix theory
Spin interactions beteween two moving Dp-branes are analyzed using the
Green-Schwarz formalism of boundary states. This approach turns out to be
extremely efficient to compute all the spin effects related by supersymmetry to
the leading v^4/r^7-p term. All these terms are shown to be scale invariant,
supporting a matrix model description of supergravity interactions. By
employing the LSZ reduction formula for matrix theory and the mentioned
supersymmetric effective potential for D0-branes, we compute the t-pole of
graviton-graviton and three form-three form scattering in matrix theory. The
results are found to be in complete agreement with tree level supergravity in
the corresponding kinematical regime and provide, moreover, an explicit map
between these degrees of freedom in both theories.Comment: 8 pages, no figures, talk presented at the conference "Quantum
aspects of gauge theories, supergravity and unification", Corfu, Greece, to
appear in the proceeding
Gravitational couplings of orientifold planes
We reanalyse the gravitational couplings of the perturbative orientifold
planes , (and D-branes). We first compute their
instantonic corrections for . Then, by using U-dualities, we obtain the
Wess-Zumino terms of orientifolds with RR flux for . The expressions
for the effective actions can be partially checked via M-theory. We point out a
previous oversimplification and we show in fact that the difficulty still
stands in the way of the full computation of 7 Brane instanton corrections.Comment: 13 pages, 1 figure, 2 tables. 3 references adde
Holographic Description of Gravitational Anomalies
The holographic duality can be extended to include quantum theories with
broken coordinate invariance leading to the appearance of the gravitational
anomalies. On the gravity side one adds the gravitational Chern-Simons term to
the bulk action which gauge invariance is only up to the boundary terms. We
analyze in detail how the gravitational anomalies originate from the modified
Einstein equations in the bulk. As a side observation we find that the
gravitational Chern-Simons functional has interesting conformal properties. It
is invariant under conformal transformations. Moreover, its metric variation
produces conformal tensor which is a generalization of the Cotton tensor to
dimension . We calculate the modification of the holographic
stress-energy tensor that is due to the Chern-Simons term and use the bulk
Einstein equations to find its divergence and thus reproduce the gravitational
anomaly. Explicit calculation of the anomaly is carried out in dimensions
and . The result of the holographic calculation is compared with that of
the descent method and agreement is found. The gravitational Chern-Simons term
originates by Kaluza-Klein mechanism from a one-loop modification of M-theory
action. This modification is discussed in the context of the gravitational
anomaly in six-dimensional theory. The agreement with earlier
conjectured anomaly is found.Comment: 24 pages, Latex; presentation re-structured, new references adde
Supersymmetric Dissipative Quantum Mechanics from Superstrings
Following the approach of Callan and Thorlacius applied to the superstring,
we derive a supersymmetric extension of the non-local dissipative action of
Caldeira and Leggett. The dissipative term turns out to be invariant under a
group of superconformal transformations. When added to the usual kinetic term,
it provides an example of supersymmetric dissipative quantum mechanics. As a
by-product of our analysis, an intriguing connection to the homeotic/hybrid
fermion model, proposed for CPT violation in neutrinos, appears.Comment: Latex, 16 page
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