Spatiotemporal NF-κB dynamics encodes the position, amplitude, and duration of local immune inputs

Infected cells communicate through secreted signaling molecules like cytokines, which carry information about pathogens. How differences in cytokine secretion affect inflammatory signaling over space and how responding cells decode information from propagating cytokines are not understood. By computationally and experimentally studying NF-κB dynamics in cocultures of signal-sending cells (macrophages) and signal-receiving cells (fibroblasts), we find that cytokine signals are transmitted by wave-like propagation of NF-κB activity and create well-defined activation zones in responding cells. NF-κB dynamics in responding cells can simultaneously encode information about cytokine dose, duration, and distance to the cytokine source. Spatially resolved transcriptional analysis reveals that responding cells transmit local cytokine information to distance-specific proinflammatory gene expression patterns, creating "gene expression zones."Despite single-cell variability, the size and duration of the signaling zone are tightly controlled by the macrophage secretion profile. Our results highlight how macrophages tune cytokine secretion to control signal transmission distance and how inflammatory signaling interprets these signals in space and time

Planar photonic crystals infiltrated with nanoparticle/polymer composites

© 2007 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.2817964DOI: 10.1063/1.2817964Infiltration of planar two-dimensional silicon photonic crystals with nanocomposites using a simple yet effective melt processing technique is presented. The nanocomposites that were developed by evenly dispersing functionalized TiO₂ nanoparticles into a photoconducting polymer were completely filled into photonic crystals with hole sizes ranging from 90 to 500 nm. The infiltrated devices show tuning of the photonic band gap that is controllable by the adjustment of the nanoparticle loading level. These results may be useful in the development of tunable photonic crystal based devices and hybrid light emitting diodes and solar cells

High-performance photorefractive polymer operating at 1550 nm with near-video-rate response time

© 2005 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.2117610DOI: 10.1063/1.2117610The development of a high-performance photorefractive polymer composite operating at 1550 nm is reported. We show 40% internal diffraction efficiency with response time of 35 ms and a net gain of 20 cm ⁻¹ in four-wave mixing and two-beam coupling experiments, respectively. This is more than an order of magnitude improvement in the diffraction efficiency and net two beam coupling gain and two orders of magnitude in the response time than the previously reported photorefractive polymer operating at this technologically important wavelength. The improvement in photorefractive characteristics is accomplished by an enhanced orientation of the nonlinear optical chromophore in the present composit

Microfluidic cell culture

Microfluidic techniques allow precise control of fluids and particles at the nanoliter scale and facilitate simultaneous manipulation and analysis of cultured cells, starting from a single cell to larger populations and to intact tissues. The use of integrated microfluidic devices has considerably advanced the fields of quantitative and systems biology. In this review, we survey the recent developments in microfluidic cell culture, and discuss not only the advantages but also limitations of using such systems, and give an outlook on potential future developments

Computer vision reveals hidden variables underlying NF-ΚB activation in single cells

Individual cells are heterogeneous when responding to environmental cues. Under an external signal, certain cells activate gene regulatory pathways, while others completely ignore that signal. Mechanisms underlying cellular heterogeneity are often inaccessible because experiments needed to study molecular states destroy the very states that we need to examine. Here, we developed an image-based support vector machine learning model to uncover variables controlling activation of the immune pathway nuclear factor ΚB (NF-ΚB). Computer vision analysis predicts the identity of cells that will respond to cytokine stimulation and shows that activation is predetermined by minute amounts of “leaky” NF-ΚB (p65:p50) localization to the nucleus. Mechanistic modeling revealed that the ratio of NF-ΚB to inhibitor of NF-ΚB predetermines leakiness and activation probability of cells. While cells transition between molecular states, they maintain their overall probabilities for NF-ΚB activation. Our results demonstrate how computer vision can find mechanisms behind heterogeneous single-cell activation under proinflammatory stimuli

Photorefractive polymer composite operating at the optical communication wavelength of 1550 nm

© 2004 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1826224DOI: 10.1063/1.1826224A photorefractive polymer composite sensitized at 1550 nm through direct two-photon absorption has been developed. We show an external diffraction efficiency of 3% in four-wave-mixing experiments and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer composite. Amongst other potential applications, the demonstration of accurate, dynamic aberration correction through holography in this all-organic photorefractive device presents an alternative to complex adaptive optics systems currently employed in through-air optical communication links

Digital signaling decouples activation probability and population heterogeneity

Digital signaling enhances robustness of cellular decisions in noisy environments, but it is unclear how digital systems transmit temporal information about a stimulus. To understand how temporal input information is encoded and decoded by the NF-κB system, we studied transcription factor dynamics and gene regulation under dose- and duration-modulated inflammatory inputs. Mathematical modeling predicted and microfluidic single-cell experiments confirmed that integral of the stimulus (or area, concentration × duration) controls the fraction of cells that activate NF-κB in the population. However, stimulus temporal profile determined NF-κB dynamics, cell-to-cell variability, and gene expression phenotype. A sustained, weak stimulation lead to heterogeneous activation and delayed timing that is transmitted to gene expression. In contrast, a transient, strong stimulus with the same area caused rapid and uniform dynamics. These results show that digital NF-κB signaling enables multidimensional control of cellular phenotype via input profile, allowing parallel and independent control of single-cell activation probability and population heterogeneity

High-performance photorefractive polymer operating at 975 nm

© 2004 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.1780591DOI: 10.1063/1.1780591A family of photorefractive polymer composites has been developed that enable high-performance device operation at a wavelength of 975 nm. This constitutes a major extension into the near-infrared spectral region for the operation of all-organic photorefractive devices. Utilizing our photorefractive materials, we demonstrate large net two-beam coupling gain of more than 100 cm ⁻¹ 60% diffraction efficiency in four-wave mixing experiments, and a fast response time of 33 ms, at an irradiance of 1 W/cm²