Specification of cell fate in the sea urchin embryo: summary and some proposed mechanisms

An early set of blastomere specifications occurs during cleavage in the sea urchin embryo, the result of both conditional and autonomous processes, as proposed in the model for this embryo set forth in 1989. Recant experimental results have greatly illuminated the mechanisms of specification in some early embryonic territories, though others remain obscure. We review the progressive process of specification within given lineage elements, and with reference to the early axial organization of the embryo. Evidence for the conditional specification of the veg(2) lineage subelement of the endoderm and other potential interblastomere signaling interactions in the cleavage-stage embryo are summarized. Definitive boundaries between mesoderm and endoderm territories of complex. the vegetal plate, and between endoderm and overlying ectoderm, are not established until later in development. These processes have been clarified by numerous observations on spatial expression of various genes, and by elegant lineage labeling studies. The early specification events depend on regional mobilization of regulatory factors resulting at once in the zygotic expression of genes encoding transcription factors, as well as downstream genes encoding proteins characteristic of the cell types that will much later arise from the progeny of the specified blastomeres. This embryo displays a maximal form of indirect development. The gene regulatory network underlying the embryonic development reflects the relative simplicity of the completed larva and of the processes required for its formation. The requirements for postembryonic adult body plan formation in the larval rudiment include engagement of a new level of genetic regulatory apparatus, exemplified by the Hox gene complex

Unmanned Aircraft Systems: Factors That Affect The Acceptance Of Unmanned Aircraft Usage Within The United States National Airspace System

Unmanned aircraft have been around since before the Wright brothers took flight in 1903. Even though unmanned aircraft have had a history that well exceeds the century of manned aviation, they were primarily used by the military, and were mostly outside the public\u27s purview. In recent years unmanned aircraft have made a giant leap from military use to commercial use within the United States and around the world. While pilots and operators flying these aircraft may have accepted the technology and its future potential; the public might have a different point of view on utilization over their home, town, state, or country. Numerous articles suggest that the public of the United States has a long history of determining which technologies will be readily accepted, slowly adopted, or fail before becoming commonplace. This thesis examines important issues regarding public perception of Unmanned Aircraft Systems (UAS), their use in the United States, where they fly, and, specifically, their use in a law enforcement setting. The study found that the public has a lower acceptance rate for unmanned aircraft than manned aircraft. Public perception of unmanned aircraft may create obstacles for the usage of this technology for law enforcement purposes

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

Eclipse Ice Core Accumulation and Stable Isotope Variability as an Indicator of North Pacific Climate

The high accumulation rate and negligible amount of melt at Eclipse Icefield (3017 m) in the Saint Elias Range of Yukon, Canada, allows for the preservation of a high-resolution isotopic and glaciochemical records valuable for reconstruction of climatic variables. Each of the three Eclipse ice cores have a well-constrained depth–age scale with dozens of reference horizons over the twentieth century that permits an exceptional level of confi- dence in the results of the current calibration exercise. Stacked time series of accumulation and stable isotopes were divided into cold and warm seasons and seasons of extreme high and extreme low accumulation and stable isotope values (eight groups). For each group, season-averaged composites of 500-hPa geopotential height grids, and the individual seasons that constitute them, were analyzed to elucidate common anomalous flow patterns. This analysis shows that the most fractionated isotopes and lowest accumulation cold seasons reflect a more zonal height pattern in the North Pacific associated with negative Pacific–North American (PNA) and Pacific decadal oscillation (PDO) indices. Conversely, the least fractionated isotopes and highest accumulation cold seasons are associated with a positive PNA pattern. Although only a maximum of approximately 20% of the total number of accumulation and stable isotope seasons exhibit a relatively consistent relationship with 500-hPa geopotential height patterns, these results support the hypothesis that the most extreme accumulation and extreme isotope cold-season values in the Saint Elias Mountains are related to consistent atmospheric circulation and oceanic sea surface temperature patterns

Comparative Analysis of Airborne Chemical Exposure to Air Force Small Arms Range Instructors

This study examines airborne chemical exposure to Air Force small arms range instructors during M16 firing of lead and lead-free bullets. Historical range information collected from 63 active duty Air Force bases identified that two thirds of the Air Force military ranges within the Continental United States are currently firing lead-free ammunition. Average 8-hr TWA exposures for lead during M16 firing of leaded ammunition were 17% of the Occupational Exposure Limit (OEL). Task exposures, representing worst case conditions, were found to be 1.2 time the OEL. Two indoor and four outdoor firing ranges currently firing frangible lead-free ammunition were evaluated through a collaborative effort with the Air Force Institute for Operational Health (AFIOH) to assess instructor exposure and current range conditions. Transition to lead-free ammunition showed a 70% reduction in lead at indoor ranges and a 41% reduction in lead at outdoor ranges. Airborne exposures generated from metals and combustion by-products associated with nylon and plastics during M16 firing of frangible lead-free ammunition were found to be well below their respective OELs. This research suggests that the average exposure levels associated with lead-free ammunition does not pose a significant threat to Air Force instructors at indoor and outdoor ranges