6,028 research outputs found
Spatial expression of Hox cluster genes in the ontogeny of a sea urchin
The Hox cluster of the sea urchin Strongylocentrous purpuratus contains ten genes in a 500 kb span of the genome. Only two of these genes are expressed during embryogenesis, while all of eight genes tested are expressed during development of the adult body plan in the larval stage. We report the spatial expression during larval development of the five 'posterior' genes of the cluster: SpHox7, SpHox8, SpHox9/10, SpHox11/13a and SpHox11/13b. The five genes exhibit a dynamic, largely mesodermal program of expression. Only SpHox7 displays extensive expression within the pentameral rudiment itself. A spatially sequential and colinear arrangement of expression domains is found in the somatocoels, the paired posterior mesodermal structures that will become the adult perivisceral coeloms. No such sequential expression pattern is observed in endodermal, epidermal or neural tissues of either the larva or the presumptive juvenile sea urchin. The spatial expression patterns of the Hox genes illuminate the evolutionary process by which the pentameral echinoderm body plan emerged from a bilateral ancestor
Hindgut specification and cell-adhesion functions of Sphox11/13b in the endoderm of the sea urchin embryo
Sphox11/13b is one of the two hox genes of Strongylocentrotus purpuratus expressed in the embryo. Its
dynamic pattern of expression begins during gastrulation, when the transcripts are transiently located in a
ring of cells at the edge of the blastopore. After gastrulation, expression is restricted to the anus–hindgut
region at the boundary between the ectoderm and the endoderm. The phenotype that results when translation
of Sphox11/13b mRNA is knocked down by treatment with morpholino antisense oligonucleotides (MASO)
suggests that this gene may be indirectly involved in cell adhesion functions as well as in the proper
differentiation of the midgut–hindgut and midgut–foregut sphincters. The MASO experiments also reveal that
Sphox11/13b negatively regulates several downstream endomesoderm genes. For some of these genes,
Sphox11/13b function is required to restrict expression to the midgut by preventing ectopic expression in the
hindgut. The evolutionary conservation of these functions indicates the general roles of posterior Hox genes
in regulating cell-adhesion, as well as in spatial control of gene regulatory network subcircuits in the
regionalizing gut
The Research Space: using the career paths of scholars to predict the evolution of the research output of individuals, institutions, and nations
In recent years scholars have built maps of science by connecting the
academic fields that cite each other, are cited together, or that cite a
similar literature. But since scholars cannot always publish in the fields they
cite, or that cite them, these science maps are only rough proxies for the
potential of a scholar, organization, or country, to enter a new academic
field. Here we use a large dataset of scholarly publications disambiguated at
the individual level to create a map of science-or research space-where links
connect pairs of fields based on the probability that an individual has
published in both of them. We find that the research space is a significantly
more accurate predictor of the fields that individuals and organizations will
enter in the future than citation based science maps. At the country level,
however, the research space and citations based science maps are equally
accurate. These findings show that data on career trajectories-the set of
fields that individuals have previously published in-provide more accurate
predictors of future research output for more focalized units-such as
individuals or organizations-than citation based science maps
Ucrania, en la encrucijada entre Occidente y Rusia: un acercamiento del soft al smart power
A partir de la noción de poder inteligente (smart power), que se utiliza para distinguir tres fenómenos de interacción estatal en el plano político: atracción, influencia y coerción, se analizan las acciones de Estados Unidos, la Unión Europea y Rusia hacia Ucrania, a raíz de la crisis en Crimea. Se narra la evolución del conflicto, cuya resolución es de pronóstico reservado.ITESO, A.C
Quantum Energy Expectation in Periodic Time-Dependent hamiltonians via Green Functions
Let be the Floquet operator of a time periodic hamiltonian .
For each positive and discrete observable (which we call a {\em probe
energy}), we derive a formula for the Laplace time average of its expectation
value up to time in terms of its eigenvalues and Green functions at the
circle of radius . Some simple applications are provided which support
its usefulness.Comment: 31 page
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