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In Toxoplasma gondii, cis-acting elements present in promoter sequences of genes that are stage-specifically regulated have been described. However, the nuclear factors that bind to these cis-acting elements and regulate promoter activities have not been identified. In the present study, we performed affinity purification, followed by proteomic analysis, to identify nuclear factors that bind to a stage-specific promoter in T. gondii. This led to the identification of several nuclear factors in T. gondii including a novel factor, designated herein as TgNF3. The N-terminal domain of TgNF3 shares similarities with the N-terminus of yeast nuclear FK506-binding protein (FKBP), known as a histone chaperone regulating gene silencing. Using anti-TgNF3 antibodies, HA-FLAG and YFP-tagged TgNF3, we show that TgNF3 is predominantly a parasite nucleolar, chromatin-associated protein that binds specifically to T. gondii gene promoters in vivo. Genome-wide analysis using chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) identified promoter occupancies by TgNF3. In addition, TgNF3 has a direct role in transcriptional control of genes involved in parasite metabolism, transcription and translation. The ectopic expression of TgNF3 in the tachyzoites revealed dynamic changes in the size of the nucleolus, leading to a severe attenuation of virulence in vivo. We demonstrate that TgNF3 physically interacts with H3, H4 and H2A/H2B assembled into bona fide core and nucleosome-associated histones. Furthermore, TgNF3 interacts specifically to histones in the context of stage-specific gene silencing of a promoter that lacks active epigenetic acetylated histone marks. In contrast to virulent tachyzoites, which express the majority of TgNF3 in the nucleolus, the protein is exclusively located in the cytoplasm of the avirulent bradyzoites. We propose a model where TgNF3 acts essentially to coordinate nucleolus and nuclear functions by modulating nucleosome activities during the intracellular proliferation of the virulent tachyzoites of T. gondii., Author Summary Apicomplexa including Toxoplasma gondii are responsible for a variety of deadly infections. These intracellular parasites have complex life cycles within different hosts and their infectivity relies on their capacity to regulate gene expression in response to different environments. However, to date, little is known about nuclear factors that regulate their gene expression. Here, we have characterized parasite nuclear factors that bind to a stage-specific promoter. We identified several nuclear factors including a novel factor, designated herein as TgNF3. The N-terminal domain of TgNF3 shares similarities with the N-terminus of yeast nuclear FK506-binding protein (FKBP), known as a histone chaperone regulating gene silencing. We show that TgNF3 is predominantly a nucleolar, chromatin-associated protein that specifically binds to T. gondii nucleosome-associated histones and promoters. Genome-wide analysis identified promoter occupancies by TgNF3 and we demonstrated a direct role for this factor in transcriptional control of genes involved in parasite metabolism, transcription and translation. Ectopic expression of TgNF3 induces dynamic changes in the size of the nucleolus, and a severe attenuation of parasite virulence in vivo. In avirulent bradyzoites, TgNF3 is found exclusively in the cytoplasm, suggesting a potential role in regulating nucleolar and nuclear functions in the virulent tachyzoites of T. gondii.

We have identified and characterized a Macrophage Migration Inhibitory Factor (MIF) family member in the Lophotrochozoan invertebrate, Biomphalaria glabrata, the snail intermediate host of the human blood fluke Schistosoma mansoni. In mammals, MIF is a widely expressed pleiotropic cytokine with potent pro-inflammatory properties that controls cell functions such as gene expression, proliferation or apoptosis. Here we show that the MIF protein from B. glabrata (BgMIF) is expressed in circulating immune defense cells (hemocytes) of the snail as well as in the B. glabrata embryonic (Bge) cell line that has hemocyte-like features. Recombinant BgMIF (rBgMIF) induced cell proliferation and inhibited NO-dependent p53-mediated apoptosis in Bge cells. Moreover, knock-down of BgMIF expression in Bge cells interfered with the in vitro encapsulation of S. mansoni sporocysts. Furthermore, the in vivo knock-down of BgMIF prevented the changes in circulating hemocyte populations that occur in response to an infection by S. mansoni miracidia and led to a significant increase in the parasite burden of the snails. These results provide the first functional evidence that a MIF ortholog is involved in an invertebrate immune response towards a parasitic infection and highlight the importance of cytokines in invertebrate-parasite interactions., Author Summary Schistosoma mansoni, a parasitic blood fluke that causes intestinal schistosomiasis in humans, requires an intermediate host, a freshwater snail of the genus Biomphalaria for its transmission. Infection of the snail triggers marked cellular and humoral immune responses, but the molecular mechanisms of these responses are not well known. We have identified and characterized the involvement of a snail homologue of the cytokine MIF (Macrophage Migration Inhibitory Factor) in the snail immune responses to infection by the parasite. By using biochemical and molecular approaches in combination with in vitro culture and in vivo gene knock down, we have demonstrated the role of snail MIF in the regulation of the snail innate immune system. In particular, MIF regulates the proliferation and activation of the hemocytes, the macrophage-like snail defense cells, and the encapsulation response. This shows for the first time that MIF has a conserved cytokine function in an invertebrate and underlines the interest of the schistosome-snail model in the study of innate immunity.

Generalized skin sensitization is a main drawback of photodynamic therapy with systemic administration of photosensitizers. We have evaluated the potential use of an intratumoral injection of a liposomal formulation of mTHPC (Foslip) in a mouse model of local recurrence of breast cancer.Mice were directly injected into the tumor (IT) with 25 microl of a Foslip suspension (0.15 mg/ml) and illumination (652 nm, 20 J/cm(2)) was performed at different time points with pathological assessment after 48 hours. In a parallel mice series plasma samples were obtained at different endpoints after IT Foslip injection for HPLC analysis and the tumors were subjected in toto to macrofluorescence imaging. Fluorescence polarization measurements were conducted in vitro to estimate the rate of sensitizer redistribution from liposomes.Optimal, albeit partial, cure rates were obtained at 24 hours post-sensitizer and uninistration. Inhomogeneous and weak fluorescence was observed at early time points and became maximal at 24 hours. Plasma levels of mTHPC increased until 15 hours. Fluorescence polarization measurements showed a slow sensitizer transfer from liposomes to model membranes.The weak intratumoral fluorescence at early time points could be explained by concentration quenching within the liposomes as evidenced from fluorescence polarization studies. Progressive mTHPC redistribution from liposomes and its further incorporation into tumor tissue resulted in fluorescence build-up over time with a maximum at 24 hours post-injection. This correlates perfectly with the best therapeutic effect at this time point. The absence of total cure can be attributed to inhomogeneous photosensitizer distribution. mTHPC is reabsorbed into the blood stream but the total administered amount is much reduced as opposed to systemic administration so that repeated PDT sessions might be favorable in terms of side effects and tumor response.

As a comparatively non-destructive imaging technique into living specimens, fluorescence microscopy has a number of strong advantages over alternative imaging modalities (X-ray, MRI, CT-scan, arthro-scan, etc..). The limited analysis in thick tissue has given rise to the development of other techniques, multiphoton excitation microscopy in particular. A need for increased sensitivity and resolution has been driving the development of new sophisticated fluorescence techniques based on microscopies to study: the tissue microstructure in situ (CLSM, SHG) on deeper thick sections of tissue (multiphoton), molecular diffusion (FRAP, FCS) with fluorescent protein variants and molecular interaction (spectral, FRET, FLIM). In this paper, we have considered developments based on near infrared (NIR) femtosecond excitation in the imaging of articular tissue and discussed the technical limitations and perspectives.

International audience; In articular hyaline cartilage, chondrocytes are surrounded by an extracellular matrix which is mainly composed by collagen and proteoglycanes. Pathological specimens show a partial or complete degradation of this matrix. Therefore, it could be interesting to know how mechanical or biochemical constraints applied to cartilage specimens induce modifications of the cartilage network. Multiphoton technology combined to Second Harmonic Generation (SHG) enables to image cartilage specimens in a non-invasive mode with high resolution at deep penetration. By placing a band pass filter in front of the transmitted light detector, SHG signal with frequency doubled can be isolated for a new contrast imaging. SHG (second harmonic generation) is a diffusion process generated from organized structures and does not need any fluorescent staining. Due to their non-centrosymetric structure, collagen fibrilles present a high second-order non-linear susceptibility and thus give rise to a strong SHG signal when exposed to high enough electric fields produced by a focal point of a femtosecond pulsed laser (multiphoton microscopy). As the extracellular matrix of cartilage is in part constituted by collagen fibers, it can be imaged with this contrast tool. The intensity of SHG signals strongly depends on the organization of collagen fibers. Thus a modification of the extracellular matrix in terms of 3D-organization of collagen induced by mechanical stress can be shown with this contrast tool.

One of the major limitations when imaging biological tissues results in their thickness and opacity. To overcome these limitations and to visualize some structures of interest and to precise the relationship between the structure and the biological function [6], new imaging methods have been developed. Confocal Laser Scanning Microscopy (CLSM) is the reference technique for biological imaging. But CLSM induces some problems of photo toxicity for tissue which are observed in hard conditions. To overcome this gap, linear optical microscopy also called multiphoton microscopy continues to prove its useful for imaging live tissues in particular with reduced toxicity [9,10]. Multiphoton imaging is noninvasive, by keeping the cells alive and enables to be close to physiological conditions and allows a deeper penetration into samples [3,11] than more usual UV-visible techniques [7]. MP-excitation needs a quasi simultaneous absorption of two (or 3) photons, that means a spatio-temporal confinement of photons. A way to satisfy it and to bring a molecule into its excited state consists in using short impulsions at very high frequency. To come back to its fundamental state, many desexcitation ways among which fluorescence emission are possible. The emitted signal is specific to a molecule and its physicochemical environment and can be resolved as well spatially as temporally or spectrally. Some new tools have been developed to obtain complementary information. FLIM (Fluorescence Lifetime Imaging Microscopy) provides a discrimination of molecules on their different lifetimes (contrast image) whereas their emission spectra overlap. Importantly, the lifetime value measured for by FLIM is a property of individual fluorescent molecules and is therefore largely independent of fluorophore concentration and photobleaching [5]. In addition, the emission of specific fluorophores can be contrasted against a strong auto-fluorescence background as encountered in many biological tissues.

Apicomplexan parasites including Toxoplasma gondii have complex life cycles within different hosts and their infectivity relies on their capacity to regulate gene expression. However, little is known about the nuclear factors that regulate gene expression in these pathogens. Here, we report that T. gondii enolase TgENO2 is targeted to the nucleus of actively replicating parasites, where it specifically binds to nuclear chromatin in vivo. Using a ChIP-Seq technique, we provide evidence for TgENO2 enrichment at the 5′ untranslated gene regions containing the putative promoters of 241 nuclear genes. Ectopic expression of HA-tagged TgENO1 or TgENO2 led to changes in transcript levels of numerous gene targets. Targeted disruption of TgENO1 gene results in a decrease in brain cyst burden of chronically infected mice and in changes in transcript levels of several nuclear genes. Complementation of this knockout mutant with ectopic TgENO1-HA fully restored normal transcript levels. Our findings reveal that enolase functions extend beyond glycolytic activity and include a direct role in coordinating gene regulation in T. gondii.

Toxoplasma gondii motility, which is essential for host cell entry, migration through host tissues, and invasion, is a unique form of actin-dependent gliding. It is powered by a motor complex mainly composed of myosin heavy chain A, myosin light chain 1, gliding associated proteins GAP45, and GAP50, the only integral membrane anchor so far described. In the present study, we have combined glycomic and proteomic approaches to demonstrate that all three potential N-glycosylated sites of GAP50 are occupied by unusual N-glycan structures that are rarely found on mature mammalian glycoproteins. Using site-directed mutagenesis, we show that N-glycosylation is a prerequisite for GAP50 transport from the endoplasmic reticulum to the Golgi apparatus and for its subsequent delivery into the inner complex membrane. Assembly of key partners into the gliding complex, and parasite motility are severely impaired in the unglycosylated GAP50 mutants. Furthermore, comparative affinity purification using N-glycosylated and unglycosylated GAP50 as bait identified three novel hypothetical proteins including the recently described gliding associated protein GAP40, and we demonstrate that N-glycans are required for efficient binding to gliding partners. Collectively, these results provide the first detailed analyses of T. gondii N-glycosylation functions that are vital for parasite motility and host cell entry.

In tissue, cells are obliged to confine and adapt to a specific geometric shape due to the surrounding environmental constraints. Under healthy conditions, fibroblasts present an elongated shape; however, changes in biochemical and physical properties of the extracellular matrix could distort the cell shape, inducing a pathological state. We have studied fibroblasts’ mechanical behavior under circular geometrical constraints. Circular micropatterns force fibroblasts to acquire a different shape from that of a healthy tissue, inducing a possible pathological condition. In total, three different fibroblast types from Dupuytren’s disorder, all obtained from the same patient, were confined in circular-shaped micropatterns of three different diameters (25, 35, and 45 µm), and mechanical properties were evaluated using an atomic force microscope (AFM). We found that control fibroblast mechanics (apparent Young’s modulus) increases with the increasing pattern diameter and comes together with a decrease in cell height and in loss tangent, translated into a more solid-like behavior. We hypothesize that these results resemble the transition toward the myofibroblast phenotype, ameliorating cytoskeleton formation and organization and enhancing cell contraction. Scar and Dupuytren fibroblasts did not display major changes in cell mechanics and cell height when changing the pattern diameter, suggesting that they are less affected by physical changes in the environment as they can adapt their shape to the geometrical dimensions. Therefore, our findings demonstrate that combining micropatterning and AFM measurements provides a powerful tool to study cell mechanics inducing constraints onto the cell, thus mimicking certain aspects of the tissue environment in both healthy and pathological states.