Meiosis in mammalian oocytes is paused until luteinizing hormone (LH) activates receptors in the mural granulosa cells of the ovarian follicle. Prior work has established the central role of cyclic GMP (cGMP) from the granulosa cells in maintaining meiotic arrest, but it is not clear how binding of LH to receptors that are located up to 10 cell layers away from the oocyte lowers oocyte cGMP and restarts meiosis. Here, by visualizing intercellular trafficking of cGMP in real-time in live follicles from mice expressing a FRET sensor, we show that diffusion of cGMP through gap junctions is responsible not only for maintaining meiotic arrest, but also for rapid transmission of the signal that reinitiates meiosis from the follicle surface to the oocyte. Before LH exposure, the cGMP concentration throughout the follicle is at a uniformly high level of ∼2-4 μM. Then, within 1 min of LH application, cGMP begins to decrease in the peripheral granulosa cells. As a consequence, cGMP from the oocyte diffuses into the sink provided by the large granulosa cell volume, such that by 20 min the cGMP concentration in the follicle is uniformly low, ∼100 nM. The decrease in cGMP in the oocyte relieves the inhibition of the meiotic cell cycle. This direct demonstration that a physiological signal initiated by a stimulus in one region of an intact tissue can travel across many layers of cells via cyclic nucleotide diffusion through gap junctions could provide a general mechanism for diverse cellular processes.cyclic GMP | gap junctions | ovarian follicle | oocyte meiosis | luteinizing hormone M eiosis in mammalian oocytes begins during embryonic development and then arrests in late prophase, for up to 50 y in women and for many months in mice. At the time of ovulation, luteinizing hormone (LH) acts on the granulosa cells of the follicle surrounding the oocyte to release the arrest and restart meiosis in preparation for fertilization (1-3). In the mouse preovulatory follicle, inhibition of meiotic progression is dependent upon the cyclic nucleotide cyclic GMP (cGMP), which diffuses from the granulosa cells into the oocyte through gap junctions that connect all cells of the follicle (4-6). The cGMP is produced by the transmembrane guanylyl cyclase natriuretic peptide receptor 2 (NPR2, also known as guanylyl cyclase B), which is present in all of the granulosa cells, but not in the oocyte (7-11). In the oocyte, cGMP inhibits the degradation of another cyclic nucleotide, cAMP, which depends primarily on the phosphodiesterase PDE3A, an enzyme whose activity is antagonized by cGMP (4, 5). The resulting high level of cAMP, through a series of intermediate steps, inhibits meiotic progression (2, 3, 12).LH signaling is initiated in the outer (mural) layers of granulosa cells; receptors for LH are absent in the oocyte and in the granulosa cells that directly surround it (the cumulus cells) (13-15). Ensuing events cause meiosis to resume by reducing cGMP in the oocyte (4, 5), but how LH receptor activation up to 10 cell layers away lowers oocyt...

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Rationale Cyclic GMP (cGMP) is an important intracellular signaling molecule in the cardiovascular system, but its spatiotemporal dynamics in vivo is largely unknown. Objective To generate and characterize transgenic mice expressing the fluorescence resonance energy transfer–based ratiometric cGMP sensor, cGMP indicator with an EC50 of 500 nmol/L (cGi500), in cardiovascular tissues. Methods and Results Mouse lines with smooth muscle–specific or ubiquitous expression of cGi500 were generated by random transgenesis using an SM22α promoter fragment or by targeted integration of a Cre recombinase–activatable expression cassette driven by the cytomegalovirus early enhancer/chicken β-actin/β-globin promoter into the Rosa26 locus, respectively. Primary smooth muscle cells isolated from aorta, bladder, and colon of cGi500 mice showed strong sensor fluorescence. Basal cGMP concentrations were <100 nmol/L, whereas stimulation with cGMP-elevating agents such as 2-(N,N-diethylamino)-diazenolate-2-oxide diethylammonium salt (DEA/NO) or the natriuretic peptides, atrial natriuretic peptide, and C-type natriuretic peptide evoked fluorescence resonance energy transfer changes corresponding to cGMP peak concentrations of ≈3 µmol/L. However, different types of smooth muscle cells had different sensitivities of their cGMP responses to DEA/NO, atrial natriuretic peptide, and C-type natriuretic peptide. Robust nitric oxide–induced cGMP transients with peak concentrations of ≈1 to >3 µmol/L could also be monitored in blood vessels of the isolated retina and in the cremaster microcirculation of anesthetized mice. Moreover, with the use of a dorsal skinfold chamber model and multiphoton fluorescence resonance energy transfer microscopy, nitric oxide–stimulated vascular cGMP signals associated with vasodilation were detected in vivo in an acutely untouched preparation. Conclusions These cGi500 transgenic mice permit the visualization of cardiovascular cGMP signals in live cells, tissues, and mice under normal and pathological conditions or during pharmacotherapy with cGMP-elevating drugs.

Sniffing out atherosclerosis Olfactory receptors are best known for their presence in the nose and their role in detecting smells, but they are also present in other tissues and perform additional biological functions. For example, vascular macrophages involved in the pathogenesis of atherosclerosis express multiple subtypes of olfactory receptors. Orecchioni et al . focused on olfactory receptor 2, a receptor for the compound octanal, and identified its contribution to atherosclerosis pathogenesis and the formation of atherosclerotic plaques (see the Perspective by Rayner and Rasheed). The authors show that most of the octanal was not directly derived from the diet, but rather was generated as a by-product of lipid peroxidation, suggesting a potential pathway for intervention. —YN

g Varicella-zoster virus (VZV) is the causative agent of chickenpox and herpes zoster (shingles). After the primary infection, the virus remains latent in sensory ganglia and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine is highly attenuated in the skin and yet retains its neurovirulence and may reactivate and damage sensory neurons. The factors involved in neuronal invasion and establishment of latency are still elusive. Previously, we constructed a library of whole-gene deletion mutants carrying a bacterial artificial chromosome sequence and a luciferase marker in order to perform a comprehensive VZV genome functional analysis. Here, screening of dispensable gene deletion mutants in differentiated neuronal cells led to the identification of ORF7 as the first known, likely a main, VZV neurotropic factor. ORF7 is a virion component localized to the Golgi compartment in infected cells, whose deletion causes loss of polykaryon formation in epithelial cell culture. Interestingly, ORF7 deletion completely abolishes viral spread in human nervous tissue ex vivo and in an in vivo mouse model. This finding adds to our previous report that ORF7 is also a skin-tropic factor. The results of our investigation will not only lead to a better understanding of VZV neurotropism but could also contribute to the development of a neuroattenuated vaccine candidate against shingles or a vector for delivery of other antigens. V aricella-zoster virus (VZV), upon encountering a naïve host, causes a primary infection commonly known as chickenpox (varicella) (1, 4, 5). The disease is generally considered mild and self-resolving even in the absence of treatment (2), although occasionally it has severe and lethal consequences (9, 23). The virus reaches sensory nerve ganglia, where it remains latent for life, unless temporary or permanent immunosuppressive conditions within the host facilitate its reactivation as shingles or herpes zoster (HZ) affecting thoracic, cranial, or lumbosacral dermatomes. Many patients report excruciating and relentless pain during HZ episodes (16,34,36,44). The reactivation is sometimes associated with postherpetic neuralgia (PHN), a severe pain along the affected sensory nerves that can linger for years even after the herpetic rash resolves (4). The drug treatments available to date against VZV-elicited diseases are useful only in alleviating some of the symptoms and in shortening the disease duration but cannot clear the virus or prevent establishment of latency (27,30). PHN is difficult to manage, especially in the elderly, who frequently suffer from other age-related conditions, and the use of the standard PHN treatment, including tricyclic antidepressants, anticonvulsants, and opioids, can be hazardous (16,36).Chickenpox was a ubiquitous childhood disease before the anti-VZV vaccination was mandated in 1995 in the United States. Since then, the numbers of hospitalizati...

Mechanisms that limit thrombosis are poorly defined. One of the few known endogenous platelet inhibitors is nitric oxide (NO). NO activates NO sensitive guanylyl cyclase (NO-GC) in platelets, resulting in an increase of cyclic guanosine monophosphate (cGMP). Here we show, using cGMP sensor mice to study spatiotemporal dynamics of platelet cGMP, that NO-induced cGMP production in pre-activated platelets is strongly shear-dependent. We delineate a new mode of platelet-inhibitory mechanotransduction via shear-activated NO-GC followed by cGMP synthesis, activation of cGMP-dependent protein kinase I (cGKI), and suppression of Ca2+ signaling. Correlative profiling of cGMP dynamics and thrombus formation in vivo indicates that high cGMP concentrations in shear-exposed platelets at the thrombus periphery limit thrombosis, primarily through facilitation of thrombus dissolution. We propose that an increase in shear stress during thrombus growth activates the NO-cGMP-cGKI pathway, which acts as an auto-regulatory brake to prevent vessel occlusion, while preserving wound closure under low shear.

The tyrosine phosphatase CD45 is a major gatekeeper for restraining T cell activation. Its exclusion from the immunological synapse (IS) is crucial for T cell receptor (TCR) signal transduction. Here, we use expansion super-resolution microscopy to reveal that CD45 is mostly pre-excluded from the tips of microvilli (MV) on primary T cells prior to antigen encounter. This pre-exclusion is diminished by depleting cholesterol or by engineering the transmembrane domain of CD45 to increase its membrane integration length, but is independent of the CD45 extracellular domain. We further show that brief MV-mediated contacts can induce Ca2+ influx in mouse antigen-specific T cells engaged by antigen-pulsed antigen presenting cells (APC). We propose that the scarcity of CD45 phosphatase activity at the tips of MV enables or facilitates TCR triggering from brief T cell-APC contacts before formation of a stable IS, and that these MV-mediated contacts represent the earliest step in the initiation of a T cell adaptive immune response.

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