Gold nanoshells covered with sharp rods called “spiky
gold
nanoshells” are synthesized by employing a silver-assisted
seed-growth method for heterogeneous nanoparticle syntheses at polymer/water
interfaces. It is found that silver ions in the growth solution play
an important role in forming uniform gold shells as well as regulating
the surface morphology. The optical properties of spiky gold nanoshells
are investigated by single-particle scattering measurements, single-particle
surface-enhanced Raman scattering measurements, and finite-difference
time-domain modeling. The scattering intensities from isolated spiky
nanoshells are significantly enhanced compared to those of conventional
smooth shells. Moreover, due to the abundant hot spots on spiky nanoshells,
the SERS signal is readily observed from single spiky shells with
a very small intensity variation (35%), whereas there is no detectable
signal from isolated smooth shells. These results demonstrate that
our synthetic method provides a straightforward way to organize metal
nanoparticles into well-defined assemblies with enhanced scattering
properties.
Retinoic acid-induced expression of the CD38 ectoenzyme receptor in HL-60 human myeloblastic leukemia cells is regulated by RARalpha and RXR, and enhanced or prevented cell differentiation depending on the level of expression per cell. RARalpha activation caused CD38 expression, as did RXR activation but not as effectively. Inhibition of MAPK signaling through MEK inhibition diminished the induced expression by both RARs and RXRs. Expression of CD38 enhanced retinoic acid-induced myeloid differentiation and G0 cell cycle arrest, but at higher expression levels, induced differentiation was blocked and retinoic acid induced a loss of cell viability instead. In the case of 1,25-dihydroxyvitamin D3, induced monocytic differentiation was also enhanced by CD38 and not enhanced by higher expression levels, but without induced loss of viability. Expression levels of CD38 thus regulated the cellular response to retinoic acid, either propelling cell differentiation or loss of viability. The cellular effects of CD38 thus depend on its expression level.
Tight regulation of gene expression is important for the survival of , a model bacterium of extreme stress resistance. Few studies have examined the use of regulatory RNAs as a possible contributing mechanism to ionizing radiation (IR) resistance, despite their proffered efficient and dynamic gene expression regulation under IR stress. This work presents a transcriptome-based approach for the identification of stress-responsive regulatory 5' untranslated region (5'-UTR) elements in R1 that can be broadly applied to other bacteria. Using this platform and an fluorescence screen, we uncovered the presence of a radiation-responsive regulatory motif in the 5' UTR of the DNA gyrase subunit A gene. Additional screens under HO-induced oxidative stress revealed the specificity of the response of this element to IR stress. Further examination of the sequence revealed a regulatory motif of the radiation and desiccation response (RDR) in the 5' UTR that is necessary for the recovery of from high doses of IR. Furthermore, we suggest that it is the preservation of predicted RNA structure, in addition to DNA sequence consensus of the motif, that permits this important regulatory ability. is an extremely stress-resistant bacterium capable of tolerating up to 3,000 times more ionizing radiation than human cells. As an integral part of the stress response mechanism of this organism, we suspect that it maintains stringent control of gene expression. However, understanding of its regulatory pathways remains incomplete to date. Untranslated RNA elements have been demonstrated to play crucial roles in gene regulation throughout bacteria. In this work, we focus on searching for and characterizing responsive RNA elements under radiation stress and propose that multiple levels of gene regulation work simultaneously to enable this organism to efficiently recover from exposure to ionizing radiation. The model we propose serves as a generic template to investigate similar mechanisms of gene regulation under stress that have likely evolved in other bacterial species.
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