exRNA Atlas Analysis Reveals Distinct Extracellular RNA Cargo Types and Their Carriers Present across Human Biofluids.

To develop a map of cell-cell communication mediated by extracellular RNA (exRNA), the NIH Extracellular RNA Communication Consortium created the exRNA Atlas resource (https://exrna-atlas.org). The Atlas version 4P1 hosts 5,309 exRNA-seq and exRNA qPCR profiles from 19 studies and a suite of analysis and visualization tools. To analyze variation between profiles, we apply computational deconvolution. The analysis leads to a model with six exRNA cargo types (CT1, CT2, CT3A, CT3B, CT3C, CT4), each detectable in multiple biofluids (serum, plasma, CSF, saliva, urine). Five of the cargo types associate with known vesicular and non-vesicular (lipoprotein and ribonucleoprotein) exRNA carriers. To validate utility of this model, we re-analyze an exercise response study by deconvolution to identify physiologically relevant response pathways that were not detected previously. To enable wide application of this model, as part of the exRNA Atlas resource, we provide tools for deconvolution and analysis of user-provided case-control studies.

Gel-on-a-chip: continuous, velocity-dependent DNA separation using nanoscale lateral displacement.

We studied the trajectories of polymers being advected while diffusing in a pressure driven flow along a periodic pillar nanostructure known as nanoscale deterministic lateral displacement (nanoDLD) array. We found that polymers follow different trajectories depending on their length, flow velocity and pillar array geometry, demonstrating that nanoDLD devices can be used as a continuous polymer fractionation tool. As a model system, we used double-stranded DNA (dsDNA) with various contour lengths and demonstrated that dsDNA in the range of 100-10 000 base pairs (bp) can be separated with a size-selective resolution of 200 bp. In contrast to spherical colloids, a polymer elongates by shear flow and the angle of polymer trajectories with respect to the mean flow direction decreases as the mean flow velocity increases. We developed a phenomenological model that explains the qualitative dependence of the polymer trajectories on the gap size and on the flow velocity. Using this model, we found the optimal separation conditions for dsDNA of different sizes and demonstrated the separation and extraction of dsDNA fragments with over 75% recovery and 3-fold concentration. Importantly, this velocity dependence provides a means of fine-tuning the separation efficiency and resolution, independent of the nanoDLD pillar geometry.

Integrated nanoscale deterministic lateral displacement arrays for separation of extracellular vesicles from clinically-relevant volumes of biological samples.

Extracellular vesicles (EVs) offer many opportunities in early-stage disease diagnosis, treatment monitoring, and precision therapy owing to their high abundance in bodily fluids, accessibility from liquid biopsy, and presence of nucleic acid and protein cargo from their cell of origin. Despite their growing promise, isolation of EVs for analysis remains a labor-intensive and time-consuming challenge given their nanoscale dimensions (30-200 nm) and low buoyant density. Here, we report a simple, size-based EV separation technology that integrates 1024 nanoscale deterministic lateral displacement (nanoDLD) arrays on a single chip capable of parallel processing sample fluids at rates of up to 900 µL h-1. Benchmarking the nanoDLD chip against commonly used EV isolation technologies, including ultracentrifugation (UC), UC plus density gradient, qEV size-exclusion chromatography (Izon Science), and the exoEasy Maxi Kit (QIAGEN), we demonstrate a superior yield of ∼50% for both serum and urine samples, representing the ability to use smaller input volumes to achieve the same number of isolated EVs, and a concentration factor enhancement of up to ∼3× for both sample types, adjustable to ∼60× for urine through judicious design. Further, RNA sequencing was carried out on nanoDLD- and UC-isolated EVs from prostate cancer (PCa) patient serum samples, resulting in a higher gene expression correlation between replicates for nanoDLD-isolated EVs with enriched miRNA, decreased rRNA, and the ability to detect previously reported RNA indicators of aggressive PCa. Taken together, these results suggest nanoDLD as a promising alternative technology for fast, reproducible, and automatable EV-isolation.

Nanoscale lateral displacement arrays for the separation of exosomes and colloids down to 20†nm.

Deterministic lateral displacement (DLD) pillar arrays are an efficient technology to sort, separate and enrich micrometre-scale particles, which include parasites, bacteria, blood cells and circulating tumour cells in blood. However, this technology has not been translated to the true nanoscale, where it could function on biocolloids, such as exosomes. Exosomes, a key target of 'liquid biopsies', are secreted by cells and contain nucleic acid and protein information about their originating tissue. One challenge in the study of exosome biology is to sort exosomes by size and surface markers. We use manufacturable silicon processes to produce nanoscale DLD (nano-DLD) arrays of uniform gap sizes ranging from 25 to 235 nm. We show that at low Péclet (Pe) numbers, at which diffusion and deterministic displacement compete, nano-DLD arrays separate particles between 20 to 110 nm based on size with sharp resolution. Further, we demonstrate the size-based displacement of exosomes, and so open up the potential for on-chip sorting and quantification of these important biocolloids.

Enzyme function is regulated by its localization.

To better understand how enzyme localization affects enzyme activity we studied the cellular localization of the glycosyltransferase MurG, an enzyme necessary for cell wall synthesis at the spore during sporulation in the bacterium Bacillus subtilis. During sporulation MurG was gradually enriched to the membrane at the forespore and point mutations in a MurG helical domain disrupting its localization to the membrane caused severe sporulation defects, but did not affect localization nor caused detectable defects during exponential growth. We found that this localization is dependent on the phospholipid cardiolipin, as in strains where the cardiolipin-synthesizing genes were deleted, MurG levels were diminished at the forespore. Furthermore, in this cardiolipin-less strain, MurG localization during sporulation was rescued by external addition of purified cardiolipin. These results support localization as a critical factor in the regulation of proper enzyme function and catalysis.

Abl2/Abl-related gene stabilizes actin filaments, stimulates actin branching by actin-related protein 2/3 complex, and promotes actin filament severing by cofilin.

Both Arp2/3 complex and the Abl2/Arg nonreceptor tyrosine kinase are essential to form and maintain diverse actin-based structures in cells, including cell edge protrusions in fibroblasts and cancer cells and dendritic spines in neurons. The ability of Arg to promote cell edge protrusions in fibroblasts does not absolutely require kinase activity, raising the question of how Arg might modulate actin assembly and turnover in the absence of kinase function. Arg has two distinct actin-binding domains and interacts physically and functionally with cortactin, an activator of the Arp2/3 complex. However, it was not known whether and how Arg influences actin filament stability, actin branch formation, or cofilin-mediated actin severing or how cortactin influences these reactions of Arg with actin. Arg or cortactin bound to actin filaments stabilizes them from depolymerization. Low concentrations of Arg and cortactin cooperate to stabilize filaments by slowing depolymerization. Arg stimulates formation of actin filament branches by Arp2/3 complex and cortactin. An Arg mutant lacking the C-terminal calponin homology actin-binding domain stimulates actin branch formation by the Arp2/3 complex, indicative of autoinhibition. ArgΔCH can stimulate the Arp2/3 complex even in the absence of cortactin. Arg greatly potentiates cofilin severing of actin filaments, and cortactin attenuates this enhanced severing. The ability of Arg to stabilize filaments, promote branching, and increase severing requires the internal (I/L)WEQ actin-binding domain. These activities likely underlie important roles that Arg plays in the formation, dynamics, and stability of actin-based cellular structures.

Two amino acid residues confer different binding affinities of Abelson family kinase SRC homology 2 domains for phosphorylated cortactin.

The closely related Abl family kinases, Arg and Abl, play important non-redundant roles in the regulation of cell morphogenesis and motility. Despite similar N-terminal sequences, Arg and Abl interact with different substrates and binding partners with varying affinities. This selectivity may be due to slight differences in amino acid sequence leading to differential interactions with target proteins. We report that the Arg Src homology (SH) 2 domain binds two specific phosphotyrosines on cortactin, a known Abl/Arg substrate, with over 10-fold higher affinity than the Abl SH2 domain. We show that this significant affinity difference is due to the substitution of arginine 161 and serine 187 in Abl to leucine 207 and threonine 233 in Arg, respectively. We constructed Abl SH2 domains with R161L and S187T mutations alone and in combination and find that these substitutions are sufficient to convert the low affinity Abl SH2 domain to a higher affinity "Arg-like" SH2 domain in binding to a phospho-cortactin peptide. We crystallized the Arg SH2 domain for structural comparison to existing crystal structures of the Abl SH2 domain. We show that these two residues are important determinants of Arg and Abl SH2 domain binding specificity. Finally, we expressed Arg containing an "Abl-like" low affinity mutant Arg SH2 domain (L207R/T233S) and find that this mutant, although properly localized to the cell periphery, does not support wild type levels of cell edge protrusion. Together, these observations indicate that these two amino acid positions confer different binding affinities and cellular functions on the distinct Abl family kinases.