Membrane association of active genes organizes the chloroplast nucleoid structure.

DNA is organized into chromatin-like structures that support the maintenance and regulation of genomes. A unique and poorly understood form of DNA organization exists in chloroplasts, which are organelles of endosymbiotic origin responsible for photosynthesis. Chloroplast genomes, together with associated proteins, form membrane-less structures known as nucleoids. The internal arrangement of the nucleoid, molecular mechanisms of DNA organization, and connections between nucleoid structure and gene expression remain mostly unknown. We show that Arabidopsis thaliana chloroplast nucleoids have a unique sequence-specific organization driven by DNA binding to the thylakoid membranes. DNA associated with the membranes has high protein occupancy, has reduced DNA accessibility, and is highly transcribed. In contrast, genes with low levels of transcription are further away from the membranes, have lower protein occupancy, and have higher DNA accessibility. Membrane association of active genes relies on the pattern of transcription and proper chloroplast development. We propose a speculative model that transcription organizes the chloroplast nucleoid into a transcriptionally active membrane-associated core and a less active periphery.

Microfluidic device for high-throughput affinity-based isolation of extracellular vesicles.

Immunoaffinity based EV isolation technologies use antibodies targeting surface markers on EVs to provide higher isolation specificity and purity compared to existing approaches. One standing challenge for researchers is how to release captured EVs from the substrate to increase downstream and biological studies. The strong binding between the antibody and antigen or the antibody and substrate is commonly unbreakable without operating at conditions outside of the critical physiological range, making the release of EVs problematic. Additionally, immuno-affinity approaches are usually low-throughput due to their low flow velocity to ensure adequate time for antibody-antigen binding. To overcome these limitations, we modified the OncoBean chip, a previously reported circulating tumor cell isolation microfluidic device. The OncoBean chip is a radial flow microfluidic device with bean-shape microposts functionalized with biotin-conjugated EPCAM antibody through biotin-avidin link chemistry. It was demonstrated that the high surface area and varying shear rate provided by the bean-shaped posts and the radial flow design in the chip, enabled efficient capture of CTCs at high flow rate. We replace the anti-EPCAM with antibodies that recognize common EV surface markers to achieve high-throughput EV isolation. Moreover, by incorporating desthiobiotin-conjugated antibodies, EVs can be released from the device after capture, which offers a significant improvement over the existing isolation. The released EVs were found to be functional by confirming their uptake by cells using flow cytometry and fluorescent microscopy. We believe the proposed technology can facilitate both the study of EVs as cell-to-cell communicators and the further identification of EV markers.