Genome-wide assessment of differential effector gene use in embryogenesis

Six different populations of cells were isolated by FACS from disaggregated late blastula and gastrula stage sea urchin embryos according to the regulatory states expressed in these cells, as reported by recombineered BACs producing fluorochromes. Transcriptomes recovered from these embryonic cell populations revealed striking, early differential expression of large cohorts of effector genes. The six cell populations were presumptive pigment cells, presumptive neurogenic cells, presumptive skeletogenic cells, cells from the stomodeal region of the oral ectoderm, ciliated band cells, and cells from the endoderm/ectoderm boundary that will give rise both to hindgut and to border ectoderm. Transcriptome analysis revealed that each of these domains specifically expressed several hundred effector genes at significant levels. Annotation indicates the qualitative individuality of the functional nature of each cell population, even though they were isolated from embryos only 1 to 2 days old. In no case was more than a tiny fraction of the transcripts enriched in one population also enriched in any other of the six populations studied. As was particularly clear in the cases of the presumptive pigment, neurogenic, and skeletogenic cells, all three of which represent precociously differentiating cell types of this embryo, most specifically expressed genes of given cell types are not significantly expressed at all in the other cell types. Thus at the effector gene level a dramatic, cell type specific pattern of differential gene regulation is established well before any significant embryonic morphogenesis has occurred

Study of quasi-1D SnO2 nanowires

The descriptions of SnO2 nanowires growth procedures are getting more and more frequent in the current literature. However, studies on the growth mechanisms are still lacking. In particular, no investigation has been reported on the growth process when the growth mechanisms are not based, as in the case of whiskers, on vapour-liquid-solid (VLS) transitions. In this paper, a new procedure is reported by the authors for growing SnO2 nanowires, based on the presence of liquid-tin droplets on the substrate. The Sn vapour pressure developed by these droplets, which find themselves very close to the growing tip of the wire, gives rise to a sufficiently high supersaturation to enable the fast growth rate usually observed. The principal features and results of this new procedure, as well as possible growth mechanisms, are also discussed

Synthesis and crystal structure of C2/c Ca(Co, Mg)Si2O6 pyroxenes : effect of the cationic substitution on the cell volume

A series of clinopyroxenes along the CaMgSi2O6-CaCoSi2O6 join was synthesized by quenching from melt at 1500\ub0C and subsequent annealing at 1250\ub0C (at 0.0001 GPa). This protocol proved to be the most effective to obtain homogenous, impurity free and stoichiometric pyroxenes as run products. Electron microprobe analyses in energy-dispersive mode were conducted and single-crystal X-ray diffraction data were collected on the Ca(CoxMg1-x)Si2O6 pyroxenes, with x = 0.2, 0.4, 0.5, 0.6; anisotropic structure refinements were performed. The effects of the cation substitution at the M1 site are described at the atomic level. The experimental findings of this study allowed us to extend the comparative analysis of the structural features of pyroxenes with divalent cations at the M1 and M2 sites

The genome of the sea urchin Strongylocentrotus purpuratus

We report the sequence and analysis of the 814-megabase genome of the sea urchin Strongylocentrotus purpuratus, a model for developmental and systems biology. The sequencing strategy combined whole-genome shotgun and bacterial artificial chromosome (BAC) sequences. This use of BAC clones, aided by a pooling strategy, overcame difficulties associated with high heterozygosity of the genome. The genome encodes about 23,300 genes, including many previously thought to be vertebrate innovations or known only outside the deuterostomes. This echinoderm genome provides an evolutionary outgroup for the chordates and yields insights into the evolution of deuterostomes

Femtosecond Carrier Dynamics in In2O3Nanocrystals

We have studied carrier dynamics in In2O3nanocrystals grown on a quartz substrate using chemical vapor deposition. Transient differential absorption measurements have been employed to investigate the relaxation dynamics of photo-generated carriers in In2O3nanocrystals. Intensity measurements reveal that Auger recombination plays a crucial role in the carrier dynamics for the carrier densities investigated in this study. A simple differential equation model has been utilized to simulate the photo-generated carrier dynamics in the nanocrystals and to fit the fluence-dependent differential absorption measurements. The average value of the Auger coefficient obtained from fitting to the measurements was γ = 5.9 ± 0.4 × 10−31 cm6 s−1. Similarly the average relaxation rate of the carriers was determined to be approximately τ = 110 ± 10 ps. Time-resolved measurements also revealed ~25 ps delay for the carriers to reach deep traps states which have a subsequent relaxation time of approximately 300 ps

Structural effects on the emission properties of Pr 3+

International audienceSingle crystals of Ba 2 NaNb 5 O 15 doped with Pr 3+ have been grown from sodium tetraborate flux. Their emission properties have been measured as a function of the doping level under different excitation and temperature conditions. The experimental observations have been accounted for by considering the effects of the crystal structure, of the doping mechanisms and of the interactions between host lattice and doping ions. The proposed conclusions have been verified by means of single crystal X-ray diffraction measurements and the resulting site occupancies of the active ions have been discussed in the light of the synthesis procedure