Resident cardiac macrophages mediate adaptive myocardial remodeling

Cardiac macrophages represent a heterogeneous cell population with distinct origins, dynamics, and functions. Recent studies have revealed that C-C Chemokine Receptor 2 positive (CCR2+) macrophages derived from infiltrating monocytes regulate myocardial inflammation and heart failure pathogenesis. Comparatively little is known about the functions of tissue resident (CCR2-) macrophages. Herein, we identified an essential role for CCR2- macrophages in the chronically failing heart. Depletion of CCR2- macrophages in mice with dilated cardiomyopathy accelerated mortality and impaired ventricular remodeling and coronary angiogenesis, adaptive changes necessary to maintain cardiac output in the setting of reduced cardiac contractility. Mechanistically, CCR2- macrophages interacted with neighboring cardiomyocytes via focal adhesion complexes and were activated in response to mechanical stretch through a transient receptor potential vanilloid 4 (TRPV4)-dependent pathway that controlled growth factor expression. These findings establish a role for tissue-resident macrophages in adaptive cardiac remodeling and implicate mechanical sensing in cardiac macrophage activation.

Maturation of Heterogeneity in Afferent Synapse Ultrastructure in the Mouse Cochlea

Auditory nerve fibers (ANFs) innervating the same inner hair cell (IHC) may have identical frequency tuning but different sound response properties. In cat and guinea pig, ANF response properties correlate with afferent synapse morphology and position on the IHC, suggesting a causal structure-function relationship. In mice, this relationship has not been fully characterized. Here we measured the emergence of synaptic morphological heterogeneities during maturation of the C57BL/6J mouse cochlea by comparing postnatal day 17 (p17, ∼3 days after hearing onset) with p34, when the mouse cochlea is mature. Using serial block face scanning electron microscopy and three-dimensional reconstruction we measured the size, shape, vesicle content, and position of 70 ribbon synapses from the mid-cochlea. Several features matured over late postnatal development. From p17 to p34, presynaptic densities (PDs) and post-synaptic densities (PSDs) became smaller on average (PDs: 0.75 to 0.33; PSDs: 0.58 to 0.31 μm2) and less round as their short axes shortened predominantly on the modiolar side, from 770 to 360 nm. Membrane-associated synaptic vesicles decreased in number from 53 to 30 per synapse from p17 to p34. Anatomical coupling, measured as PSD to ribbon distance, tightened predominantly on the pillar side. Ribbons became less spherical as long-axes lengthened only on the modiolar side of the IHC, from 372 to 541 nm. A decreasing gradient of synaptic ribbon size along the modiolar-pillar axis was detected only at p34 after aligning synapses of adjacent IHCs to a common reference frame (median volumes in nm3 × 106: modiolar 4.87; pillar 2.38). The number of ribbon-associated synaptic vesicles scaled with ribbon size (range 67 to 346 per synapse at p34), thus acquiring a modiolar-pillar gradient at p34, but overall medians were similar at p17 (120) and p34 (127), like ribbon surface area (0.36 vs. 0.34 μm2). PD and PSD morphologies were tightly correlated to each other at individual synapses, more so at p34 than p17, but not to ribbon morphology. These observations suggest that PDs and PSDs mature according to different cues than ribbons, and that ribbon size may be more influenced by cues from the IHC than the surrounding tissue.

Heterogeneity of meningeal B cells reveals a lymphopoietic niche at the CNS borders

The meninges contain adaptive immune cells that provide immunosurveillance of the central nervous system (CNS). These cells are thought to derive from the systemic circulation. Through single-cell analyses, confocal imaging, bone marrow chimeras, and parabiosis experiments, we show that meningeal B cells derive locally from the calvaria, which harbors a bone marrow niche for hematopoiesis. B cells reach the meninges from the calvaria through specialized vascular connections. This calvarial-meningeal path of B cell development may provide the CNS with a constant supply of B cells educated by CNS antigens. Conversely, we show that a subset of antigen-experienced B cells that populate the meninges in aging mice are blood-borne. These results identify a private source for meningeal B cells, which may help maintain immune privilege within the CNS.

Cryo-EM structures of human coagulation factors V and Va

Coagulation factor V (fV) is the precursor of fVa, which, together with fXa, Ca2+, and phospholipids, defines the prothrombinase complex and activates prothrombin in the penultimate step of the coagulation cascade. We solved the cryogenic electron microscopy (cryo-EM) structures of human fV and fVa at atomic (3.3 Å) and near-atomic (4.4 Å) resolution, respectively. The structure of fV reveals the entire A1-A2-B-A3-C1-C2 assembly, but with a surprisingly disordered B domain. The C1 and C2 domains provide a platform for interaction with phospholipid membranes and support the A1 and A3 domains, with the A2 domain sitting on top of them. The B domain is highly dynamic and visible only for short segments connecting to the A2 and A3 domains. The A2 domain reveals all sites of proteolytic processing by thrombin and activated protein C, a partially buried epitope for binding fXa, and fully exposed epitopes for binding activated protein C and prothrombin. Removal of the B domain and activation to fVa exposes the sites of cleavage by activated protein C at R306 and R506 and produces increased disorder in the A1-A2-A3-C1-C2 assembly, especially in the C-terminal acidic portion of the A2 domain that is responsible for prothrombin binding. Ordering of this region and full exposure of the fXa epitope emerge as necessary steps in the assembly of the prothrombin-prothrombinase complex. These structures offer molecular context for the function of fV and fVa and pioneer the analysis of coagulation factors by cryo-EM.

Targeted Therapy to β3 Integrin Reduces Chemoresistance in Breast Cancer Bone Metastases

Breast cancer bone metastases are common and incurable. Tumoral integrin β3 (β3) expression is induced through interaction with the bone microenvironment. Although β3 is known to promote bone colonization, its functional role during therapy of established bone metastases is not known. We found increased numbers of β3+ tumor cells in murine bone metastases after docetaxel chemotherapy. β3+ tumor cells were present in 97% of post-neoadjuvant chemotherapy triple-negative breast cancer patient samples (n = 38). High tumoral β3 expression was associated with worse outcomes in both pre- and postchemotherapy triple-negative breast cancer groups. Genetic deletion of tumoral β3 had minimal effect in vitro, but significantly enhanced in vivo docetaxel activity, particularly in the bone. Rescue experiments confirmed that this effect required intact β3 signaling. Ultrastructural, transcriptomic, and functional analyses revealed an alternative metabolic response to chemotherapy in β3-expressing cells characterized by enhanced oxygen consumption, reactive oxygen species generation, and protein production. We identified mTORC1 as a candidate for therapeutic targeting of this β3-mediated, chemotherapy-induced metabolic response. mTORC1 inhibition in combination with docetaxel synergistically attenuated murine bone metastases. Furthermore, micelle nanoparticle delivery of mTORC1 inhibitor to cells expressing activated αvβ3 integrins enhanced docetaxel efficacy in bone metastases. Taken together, we show that β3 integrin induction by the bone microenvironment promotes resistance to chemotherapy through an altered metabolic response that can be defused by combination with αvβ3-targeted mTORC1 inhibitor nanotherapy. Our work demonstrates the importance of the metastatic microenvironment when designing treatments and presents new, bone-specific strategies for enhancing chemotherapeutic efficacy.

Cryo-EM structure of the Rous sarcoma virus octameric cleaved synaptic complex intasome

Despite conserved catalytic integration mechanisms, retroviral intasomes composed of integrase (IN) and viral DNA possess diverse structures with variable numbers of IN subunits. To investigate intasome assembly mechanisms, we employed the Rous sarcoma virus (RSV) IN dimer that assembles a precursor tetrameric structure in transit to the mature octameric intasome. We determined the structure of RSV octameric intasome stabilized by a HIV-1 IN strand transfer inhibitor using single particle cryo-electron microscopy. The structure revealed significant flexibility of the two non-catalytic distal IN dimers along with previously unrecognized movement of the conserved intasome core, suggesting ordered conformational transitions between intermediates that may be important to capture the target DNA. Single amino acid substitutions within the IN C-terminal domain affected intasome assembly and function in vitro and infectivity of pseudotyped RSV virions. Unexpectedly, 17 C-terminal amino acids of IN were dispensable for virus infection despite regulating the transition of the tetrameric intasome to the octameric form in vitro. We speculate that this region may regulate the binding of highly flexible distal IN dimers to the intasome core to form the octameric complex. Our studies reveal key steps in the assembly of RSV intasomes.

Pandey, Bera, Shi et al. report the cryo-electron microscopy structure of the Rous sarcoma virus octameric intasome complex stabilized by a HIV-1 integrase strand transfer inhibitor. This new structure highlights the intrinsic flexibility of the distal integrase subunits and suggests that ordered conformational transitions occur within the conserved intasome core during the assembly process.

Pancreatic β-Cell-Specific Deletion of VPS41 Causes Diabetes Due to Defects in Insulin Secretion

Insulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determine this molecular composition, remain poorly understood. VPS41, a component of the endolysosomal tethering homotypic fusion and vacuole protein sorting (HOPS) complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic β-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule-regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

Cryo-EM structure of a proton-activated chloride channel TMEM206

TMEM206 has been recently identified as an evolutionarily conserved chloride channel that underlies ubiquitously expressed, proton-activated, outwardly rectifying anion currents. Here, we report the cryo-electron microscopy structure of pufferfish TMEM206, which forms a trimeric channel, with each subunit comprising two transmembrane segments and a large extracellular domain. An ample vestibule in the extracellular region is accessible laterally from the three side portals. The central pore contains multiple constrictions. A conserved lysine residue near the cytoplasmic end of the inner helix forms the presumed chloride ion selectivity filter. Unprecedentedly, the core structure and assembly closely resemble those of the epithelial sodium channel/degenerin family of sodium channels that are unrelated in amino acid sequence and conduct cations instead of anions. Together with electrophysiology, this work provides insights into ion conduction and gating for a new class of chloride channels that is architecturally distinct from previously characterized chloride channel families.

Assaying three-dimensional cellular architecture using X-ray tomographic and correlated imaging approaches

Much of our understanding of the spatial organization of and interactions between cellular organelles and macromolecular complexes has been the result of imaging studies utilizing either light- or electron-based microscopic analyses. These classical approaches, while insightful, are nonetheless limited either by restrictions in resolution or by the sheer complexity of generating multidimensional data. Recent advances in the use and application of X-rays to acquire micro- and nanotomographic data sets offer an alternative methodology to visualize cellular architecture at the nanoscale. These new approaches allow for the subcellular analyses of unstained vitrified cells and three-dimensional localization of specific protein targets and have served as an essential tool in bridging light and electron correlative microscopy experiments. Here, we review the theory, instrumentation details, acquisition principles, and applications of both soft X-ray tomography and X-ray microscopy and how the use of these techniques offers a succinct means of analyzing three-dimensional cellular architecture. We discuss some of the recent work that has taken advantage of these approaches and detail how they have become integral in correlative microscopy workflows.

Structural mechanism for gating of a eukaryotic mechanosensitive channel of small conductance

Mechanosensitive ion channels transduce physical force into electrochemical signaling that underlies an array of fundamental physiological processes, including hearing, touch, proprioception, osmoregulation, and morphogenesis. The mechanosensitive channels of small conductance (MscS) constitute a remarkably diverse superfamily of channels critical for management of osmotic pressure. Here, we present cryo-electron microscopy structures of a MscS homolog from Arabidopsis thaliana, MSL1, presumably in both the closed and open states. The heptameric MSL1 channel contains an unusual bowl-shaped transmembrane region, which is reminiscent of the evolutionarily and architecturally unrelated mechanosensitive Piezo channels. Upon channel opening, the curved transmembrane domain of MSL1 flattens and expands. Our structures, in combination with functional analyses, delineate a structural mechanism by which mechanosensitive channels open under increased membrane tension. Further, the shared structural feature between unrelated channels suggests the possibility of a unified mechanical gating mechanism stemming from membrane deformation induced by a non-planar transmembrane domain.

Mechanosensitive channels transduce physical force into electrochemical signaling in processes such as hearing, touch, proprioception, osmoregulation, and morphogenesis. Here, authors use cryo-electron microscopy to provide structural insights into the mechanical gating mechanism.

Cryo-EM structure of a neuronal functional amyloid implicated in memory persistence in Drosophila

How long-lived memories withstand molecular turnover is a fundamental question. Aggregates of a prion-like RNA-binding protein, cytoplasmic polyadenylation element-binding (CPEB) protein, is a putative substrate of long-lasting memories. We isolated aggregated Drosophila CPEB, Orb2, from adult heads and determined its activity and atomic structure, at 2.6-angstrom resolution, using cryo-electron microscopy. Orb2 formed ~75-nanometer-long threefold-symmetric amyloid filaments. Filament formation transformed Orb2 from a translation repressor to an activator and "seed" for further translationally active aggregation. The 31-amino acid protofilament core adopted a cross-β unit with a single hydrophilic hairpin stabilized through interdigitated glutamine packing. Unlike the hydrophobic core of pathogenic amyloids, the hydrophilic core of Orb2 filaments suggests how some neuronal amyloids could be a stable yet regulatable substrate of memory.

Combined Experimental Approach and Finite Element Modeling of Small Molecule Transport Through Joint Synovium to Measure Effective Diffusivity

Trans-synovial solute transport plays a critical role in the clearance of intra-articularly (IA) delivered drugs. In this study, we present a computational finite element model (FEM) of solute transport through the synovium validated by experiments on synovial explants. Unsteady diffusion of urea, a small uncharged molecule, was measured through devitalized porcine and human synovium using custom-built diffusion chambers. A multiphasic computational model was constructed and optimized with the experimental data to extract effective diffusivity for urea within the synovium. A monotonic decrease in urea concentration was observed in the donor bath over time, with an effective diffusivity found to be an order of magnitude lower in synovium versus that measured in free solution. Parametric studies incorporating an intimal cell layer with varying thickness and varying effective diffusivities were performed, revealing a dependence of drug clearance kinetics on both parameters. The findings of this study indicate that the synovial matrix impedes urea solute transport out of the joint with little retention of the solute in the matrix.

Cryo-EM structures of the ATP release channel pannexin 1

The plasma membrane adenosine triphosphate (ATP) release channel pannexin 1 (PANX1) has been implicated in many physiological and pathophysiological processes associated with purinergic signaling, including cancer progression, apoptotic cell clearance, inflammation, blood pressure regulation, oocyte development, epilepsy and neuropathic pain. Here we present near-atomic-resolution structures of human and frog PANX1 determined by cryo-electron microscopy that revealed a heptameric channel architecture. Compatible with ATP permeation, the transmembrane pore and cytoplasmic vestibule were exceptionally wide. An extracellular tryptophan ring located at the outer pore created a constriction site, potentially functioning as a molecular sieve that restricts the size of permeable substrates. The amino and carboxyl termini, not resolved in the density map, appeared to be structurally dynamic and might contribute to narrowing of the pore during channel gating. In combination with functional characterization, this work elucidates the previously unknown architecture of pannexin channels and establishes a foundation for understanding their unique channel properties.

Tmem178 negatively regulates store-operated calcium entry in myeloid cells via association with STIM1

Store-operated calcium entry (SOCE) modulates cytosolic calcium in multiple cells. Endoplasmic reticulum (ER)-localized STIM1 and plasma membrane (PM)-localized ORAI1 are two main components of SOCE. STIM1:ORAI1 association requires STIM1 oligomerization, its re-distribution to ER-PM junctions, and puncta formation. However, little is known about the negative regulation of these steps to prevent calcium overload. Here, we identified Tmem178 as a negative modulator of STIM1 puncta formation in myeloid cells. Using site-directed mutagenesis, co-immunoprecipitation assays and FRET imaging, we determined that Tmem178:STIM1 association occurs via their transmembrane motifs. Mutants that increase Tmem178:STIM1 association reduce STIM1 puncta formation, SOCE activation, impair inflammatory cytokine production in macrophages and osteoclastogenesis. Mutants that reduce Tmem178:STIM1 association reverse these effects. Furthermore, exposure to plasma from arthritic patients decreases Tmem178 expression, enhances SOCE activation and cytoplasmic calcium. In conclusion, Tmem178 modulates the rate-limiting step of STIM1 puncta formation and therefore controls SOCE in inflammatory conditions.

Characterization of the bone marrow adipocyte niche with three-dimensional electron microscopy

Unlike white and brown adipose tissues, the bone marrow adipocyte (BMA) exists in a microenvironment containing unique populations of hematopoietic and skeletal cells. To study this microenvironment at the sub-cellular level, we performed a three-dimensional analysis of the ultrastructure of the BMA niche with focused ion beam scanning electron microscopy (FIB-SEM). This revealed that BMAs display hallmarks of metabolically active cells including polarized lipid deposits, a dense mitochondrial network, and areas of endoplasmic reticulum. The distinct orientations of the triacylglycerol droplets suggest that fatty acids are taken up and/or released in three key areas - at the endothelial interface, into the hematopoietic milieu, and at the bone surface. Near the sinusoidal vasculature, endothelial cells send finger-like projections into the surface of the BMA which terminate near regions of lipid within the BMA cytoplasm. In some regions, perivascular cells encase the BMA with their flattened cellular projections, limiting contacts with other cells in the niche. In the hematopoietic milieu, BMAT adipocytes of the proximal tibia interact extensively with maturing cells of the myeloid/granulocyte lineage. Associations with erythroblast islands are also prominent. At the bone surface, the BMA extends organelle and lipid-rich cytoplasmic regions toward areas of active osteoblasts. This suggests that the BMA may serve to partition nutrient utilization between diverse cellular compartments, serving as an energy-rich hub of the stromal-reticular network. Lastly, though immuno-EM, we've identified a subset of bone marrow adipocytes that are innervated by the sympathetic nervous system, providing an additional mechanism for regulation of the BMA. In summary, this work reveals that the bone marrow adipocyte is a dynamic cell with substantial capacity for interactions with the diverse components of its surrounding microenvironment. These local interactions likely contribute to its unique regulation relative to peripheral adipose tissues.

Red blood cell phenotype fidelity following glycerol cryopreservation optimized for research purposes

Intact red blood cells (RBCs) are required for phenotypic analyses. In order to allow separation (time and location) between subject encounter and sample analysis, we developed a research-specific RBC cryopreservation protocol and assessed its impact on data fidelity for key biochemical and physiological assays. RBCs drawn from healthy volunteers were aliquotted for immediate analysis or following glycerol-based cryopreservation, thawing, and deglycerolization. RBC phenotype was assessed by (1) scanning electron microscopy (SEM) imaging and standard morphometric RBC indices, (2) osmotic fragility, (3) deformability, (4) endothelial adhesion, (5) oxygen (O2) affinity, (6) ability to regulate hypoxic vasodilation, (7) nitric oxide (NO) content, (8) metabolomic phenotyping (at steady state, tracing with [1,2,3-13C3]glucose ± oxidative challenge with superoxide thermal source; SOTS-1), as well as in vivo quantification (following human to mouse RBC xenotransfusion) of (9) blood oxygenation content mapping and flow dynamics (velocity and adhesion). Our revised glycerolization protocol (40% v/v final) resulted in >98.5% RBC recovery following freezing (-80°C) and thawing (37°C), with no difference compared to the standard reported method (40% w/v final). Full deglycerolization (>99.9% glycerol removal) of 40% v/v final samples resulted in total cumulative lysis of ~8%, compared to ~12-15% with the standard method. The post cryopreservation/deglycerolization RBC phenotype was indistinguishable from that for fresh RBCs with regard to physical RBC parameters (morphology, volume, and density), osmotic fragility, deformability, endothelial adhesivity, O2 affinity, vasoregulation, metabolomics, and flow dynamics. These results indicate that RBC cryopreservation/deglycerolization in 40% v/v glycerol final does not significantly impact RBC phenotype (compared to fresh cells).

Compound C inhibits nonsense-mediated RNA decay independently of AMPK

The nonsense mediated RNA decay (NMD) pathway safeguards the integrity of the transcriptome by targeting mRNAs with premature translation termination codons (PTCs) for degradation. It also regulates gene expression by degrading a large number of non-mutant RNAs (including mRNAs and noncoding RNAs) that bear NMD-inducing features. Consequently, NMD has been shown to influence development, cellular response to stress, and clinical outcome of many genetic diseases. Small molecules that can modulate NMD activity provide critical tools for understanding the mechanism and physiological functions of NMD, and they also offer potential means for treating certain genetic diseases and cancer. Therefore, there is an intense interest in identifying small-molecule NMD inhibitors or enhancers. It was previously reported that both inhibition of NMD and treatment with the AMPK-selective inhibitor Compound C (CC) induce autophagy in human cells, raising the possibility that CC may be capable of inhibiting NMD. Here we show that CC indeed has a NMD-inhibitory activity. Inhibition of NMD by CC is, however, independent of AMPK activity. As a competitive ATP analog, CC does not affect the kinase activity of SMG1, an essential NMD factor and the only known kinase in the NMD pathway. However, CC treatment down-regulates the protein levels of several NMD factors. The induction of autophagy by CC treatment is independent of ATF4, a NMD target that has been shown to promote autophagy in response to NMD inhibition. Our results reveal a new activity of CC as a NMD inhibitor, which has implications for its use in basic research and drug development.

The Zinc Finger Transcription Factor PLAGL2 Enhances Stem Cell Fate and Activates Expression of ASCL2 in Intestinal Epithelial Cells

Intestinal epithelial stem cell (IESC) fate is promoted by two major transcriptional regulators, the TCF4/β-catenin complex and ASCL2, which drive expression of IESC-specific factors, including Lgr5, Ephb2, and Rnf43. Canonical Wnt signaling via TCF4/β-catenin directly transactivates Ascl2, which in turn auto-regulates its own expression. Conversely, Let-7 microRNAs antagonize the IESC lineage by repressing specific mRNA targets. Here, we identify the zinc finger transcription factor PLAGL2 as a Let-7 target that regulates IESC fate. PLAGL2 drives an IESC expression signature, activates Wnt gene expression, and enhances a TCF/LEF reporter in intestinal organoids. In parallel, via cell-autonomous mechanisms, PLAGL2 is required for lineage clonal expansion and directly enhances expression of ASCL2. PLAGL2 also supports enteroid growth and survival in the context of Wnt ligand depletion. PLAGL2 expression is strongly associated with an IESC signature in colorectal cancer and may be responsible for contributing to the aberrant activation of an immature phenotype.

Modern Laser Scanning Confocal Microscopy

Since its commercialization in the late 1980's, confocal laser scanning microscopy (CLSM) has since become one of the most prevalent fluorescence microscopy techniques for three-dimensional structural studies of biological cells and tissues. The flexibility of the approach has enabled its application in a diverse array of studies, from the fast imaging of dynamic processes in living cells, to meticulous morphological analyses of tissues, and co-localization of protein expression patterns. In this chapter, we introduce the principles of confocal microscopy and discuss how the approach has become a mainstay in the biological sciences. We describe the components of a CLSM system and assess how modern implementations of the approach have further expanded the use of the technique. Finally, we briefly outline some practical considerations to take into account when acquiring data using a CLSM system. © 2018 by John Wiley & Sons, Inc.

Reciprocal Spatiotemporally Controlled Apoptosis Regulates Wolffian Duct Cloaca Fusion

The epithelial Wolffian duct (WD) inserts into the cloaca (primitive bladder) before metanephric kidney development, thereby establishing the initial plumbing for eventual joining of the ureters and bladder. Defects in this process cause common anomalies in the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). However, developmental, cellular, and molecular mechanisms of WD-cloaca fusion are poorly understood. Through systematic analysis of early WD tip development in mice, we discovered that a novel process of spatiotemporally regulated apoptosis in WD and cloaca was necessary for WD-cloaca fusion. Aberrant RET tyrosine kinase signaling through tyrosine (Y) 1062, to which PI3K- or ERK-activating proteins dock, or Y1015, to which PLCγ docks, has been shown to cause CAKUT-like defects. Cloacal apoptosis did not occur in RetY1062F mutants, in which WDs did not reach the cloaca, or in RetY1015F mutants, in which WD tips reached the cloaca but did not fuse. Moreover, inhibition of ERK or apoptosis prevented WD-cloaca fusion in cultures, and WD-specific genetic deletion of YAP attenuated cloacal apoptosis and WD-cloacal fusion in vivo Thus, cloacal apoptosis requires direct contact and signals from the WD tip and is necessary for WD-cloacal fusion. These findings may explain the mechanisms of many CAKUT.

HID-1 controls formation of large dense core vesicles by influencing cargo sorting and trans-Golgi network acidification

The peripheral membrane protein HID-1 localizes to the trans-Golgi network, where it contributes to the formation of large dense core vesicles of neuroendocrine cells by influencing cargo sorting and trans-Golgi network acidification.

Large dense core vesicles (LDCVs) mediate the regulated release of neuropeptides and peptide hormones. They form at the trans-Golgi network (TGN), where their soluble content aggregates to form a dense core, but the mechanisms controlling biogenesis are still not completely understood. Recent studies have implicated the peripheral membrane protein HID-1 in neuropeptide sorting and insulin secretion. Using CRISPR/Cas9, we generated HID-1 KO rat neuroendocrine cells, and we show that the absence of HID-1 results in specific defects in peptide hormone and monoamine storage and regulated secretion. Loss of HID-1 causes a reduction in the number of LDCVs and affects their morphology and biochemical properties, due to impaired cargo sorting and dense core formation. HID-1 KO cells also exhibit defects in TGN acidification together with mislocalization of the Golgi-enriched vacuolar H⁺-ATPase subunit isoform a2. We propose that HID-1 influences early steps in LDCV formation by controlling dense core formation at the TGN.

Bone-Induced Expression of Integrin β3 Enables Targeted Nanotherapy of Breast Cancer Metastases

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin β3 (β3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, β3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, β3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n = 42). Mechanistic investigations revealed that TGFβ signaling through SMAD2/SMAD3 was necessary for breast cancer induction of β3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin αvβ3 (αvβ3-MPs of ∼12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with αvβ3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemotherapeutics to breast cancer cells within the bone by exploiting their selective expression of integrin αvβ3 at that metastatic site. Cancer Res; 77(22); 6299-312. ©2017 AACR.

In vitro myelin formation using embryonic stem cells

Myelination in the central nervous system is the process by which oligodendrocytes form myelin sheaths around the axons of neurons. Myelination enables neurons to transmit information more quickly and more efficiently and allows for more complex brain functions; yet, remarkably, the underlying mechanism by which myelination occurs is still not fully understood. A reliable in vitro assay is essential to dissect oligodendrocyte and myelin biology. Hence, we developed a protocol to generate myelinating oligodendrocytes from mouse embryonic stem cells and established a myelin formation assay with embryonic stem cell-derived neurons in microfluidic devices. Myelin formation was quantified using a custom semi-automated method that is suitable for larger scale analysis. Finally, early myelination was followed in real time over several days and the results have led us to propose a new model for myelin formation.

Light Sheet Fluorescence Microscopy (LSFM)

The development of confocal microscopy techniques introduced the ability to optically section fluorescent samples in the axial dimension, perpendicular to the image plane. These approaches, via the placement of a pinhole in the conjugate image plane, provided superior resolution in the axial (z) dimension resulting in nearly isotropic optical sections. However, increased axial resolution, via pinhole optics, comes at the cost of both speed and excitation efficiency. Light sheet fluorescent microscopy (LSFM), a century-old idea made possible with modern developments in both excitation and detection optics, provides sub-cellular resolution and optical sectioning capabilities without compromising speed or excitation efficiency. Over the past decade, several variations of LSFM have been implemented each with its own benefits and deficiencies. Here we discuss LSFM fundamentals and outline the basic principles of several major light-sheet-based imaging modalities (SPIM, inverted SPIM, multi-view SPIM, Bessel beam SPIM, and stimulated emission depletion SPIM) while considering their biological relevance in terms of intrusiveness, temporal resolution, and sample requirements.