Fabrice de Chaumont

Icy: an open bioimage informatics platform for extended reproducible research

Current research in biology uses evermore complex computational and imaging tools. Here we describe Icy, a collaborative bioimage informatics platform that combines a community website for contributing and sharing tools and material, and software with a high-end visual programming framework for seamless development of sophisticated imaging workflows. Icy extends the reproducible research principles, by encouraging and facilitating the reusability, modularity, standardization and management of algorithms and protocols. Icy is free, open-source and available at http://icy.bioimageanalysis.org/.

Prions hijack tunnelling nanotubes for intercellular spread

In variant Creutzfeldt–Jakob disease, prions (PrPSc) enter the body with contaminated foodstuffs and can spread from the intestinal entry site to the central nervous system (CNS) by intercellular transfer from the lymphoid system to the peripheral nervous system (PNS). Although several means and different cell types have been proposed to have a role, the mechanism of cell-to-cell spreading remains elusive. Tunnelling nanotubes (TNTs) have been identified between cells, both in vitro and in vivo, and may represent a conserved means of cell-to-cell communication. Here we show that TNTs allow transfer of exogenous and endogenous PrPSc between infected and naive neuronal CAD cells. Significantly, transfer of endogenous PrPSc aggregates was detected exclusively when cells chronically infected with the 139A mouse prion strain were connected to mouse CAD cells by means of TNTs, identifying TNTs as an efficient route for PrPSc spreading in neuronal cells. In addition, we detected the transfer of labelled PrPSc from bone marrow-derived dendritic cells to primary neurons connected through TNTs. Because dendritic cells can interact with peripheral neurons in lymphoid organs, TNT-mediated intercellular transfer would allow neurons to transport prions retrogradely to the CNS. We therefore propose that TNTs are involved in the spreading of PrPSc within neurons in the CNS and from the peripheral site of entry to the PNS by neuroimmune interactions with dendritic cells.

Objective comparison of particle tracking methods

Particle tracking is of key importance for quantitative analysis of intracellular dynamic processes from time-lapse microscopy image data. Because manually detecting and following large numbers of individual particles is not feasible, automated computational methods have been developed for these tasks by many groups. Aiming to perform an objective comparison of methods, we gathered the community and organized an open competition in which participating teams applied their own methods independently to a commonly defined data set including diverse scenarios. Performance was assessed using commonly defined measures. Although no single method performed best across all scenarios, the results revealed clear differences between the various approaches, leading to notable practical conclusions for users and developers.

Learning and Survival of Newly Generated Neurons: When Time Matters

New interneurons are continually added to the olfactory bulb (OB), the first central relay for processing olfactory information, throughout life. It remains unknown how these adult-generated interneurons integrate into preexisting networks or die. We used immunohistochemical approaches to quantify adult neurogenesis in mice subjected to olfactory training. We identified a critical period in the life of an adult-generated OB interneuron, during which learning triggers distinct consequences. Using a discrimination learning task performed at various times after the birth of new interneurons, we found that olfactory training could increase, decrease, or have no effect on the number of surviving newly generated neurons. Cell survival and elimination depend on both the age of the cell and its location within the granule cell layer. This study provides new insight into the contribution of the newly generated interneurons to OB function. It demonstrates that neuronal elimination is an active process, rather than a simple consequence of nonuse.

Cellular and behavioral effects of cranial irradiation of the subventricular zone in adult mice.

Background In mammals, new neurons are added to the olfactory bulb (OB) throughout life. Most of these new neurons, granule and periglomerular cells originate from the subventricular zone (SVZ) lining the lateral ventricles and migrate via the rostral migratory stream toward the OB. Thousands of new neurons appear each day, but the function of this ongoing neurogenesis remains unclear. Methodology/Principal Findings In this study, we irradiated adult mice to impair constitutive OB neurogenesis, and explored the functional impacts of this irradiation on the sense of smell. We found that focal irradiation of the SVZ greatly decreased the rate of production of new OB neurons, leaving other brain areas intact. This effect persisted for up to seven months after exposure to 15 Gray. Despite this robust impairment, the thresholds for detecting pure odorant molecules and short-term olfactory memory were not affected by irradiation. Similarly, the ability to distinguish between odorant molecules and the odorant-guided social behavior of irradiated mice were not affected by the decrease in the number of new neurons. Only long-term olfactory memory was found to be sensitive to SVZ irradiation. Conclusion/Significance These findings suggest that the continuous production of adult-generated neurons is involved in consolidating or restituting long-lasting olfactory traces.

Ezrin tunes T-cell activation by controlling Dlg1 and microtubule positioning at the immunological synapse

T‐cell receptor (TCR) signalling is triggered and tuned at immunological synapses by the generation of signalling complexes that associate into dynamic microclusters. Microcluster movement is necessary to tune TCR signalling, but the molecular mechanism involved remains poorly known. We show here that the membrane‐microfilament linker ezrin has an important function in microcluster dynamics and in TCR signalling through its ability to set the microtubule network organization at the immunological synapse. Importantly, ezrin and microtubules are important to down‐regulate signalling events leading to Erk1/2 activation. In addition, ezrin is required for appropriate NF‐AT activation through p38 MAP kinase. Our data strongly support the notion that ezrin regulates immune synapse architecture and T‐cell activation through its interaction with the scaffold protein Dlg1. These results uncover a crucial function for ezrin, Dlg1 and microtubules in the organization of the immune synapse and TCR signal down‐regulation. Moreover, they underscore the importance of ezrin and Dlg1 in the regulation of NF‐AT activation through p38.

Tunneling nanotubes spread fibrillar α‐synuclein by intercellular trafficking of lysosomes

Synucleinopathies such as Parkinsons disease are characterized by the pathological deposition of misfolded α‐synuclein aggregates into inclusions throughout the central and peripheral nervous system. Mounting evidence suggests that intercellular propagation of α‐synuclein aggregates may contribute to the neuropathology; however, the mechanism by which spread occurs is not fully understood. By using quantitative fluorescence microscopy with co‐cultured neurons, here we show that α‐synuclein fibrils efficiently transfer from donor to acceptor cells through tunneling nanotubes (TNTs) inside lysosomal vesicles. Following transfer through TNTs, α‐synuclein fibrils are able to seed soluble α‐synuclein aggregation in the cytosol of acceptor cells. We propose that donor cells overloaded with α‐synuclein aggregates in lysosomes dispose of this material by hijacking TNT‐mediated intercellular trafficking. Our findings thus reveal a possible novel role of TNTs and lysosomes in the progression of synucleinopathies.

Disruption of Adult Neurogenesis in the Olfactory Bulb Affects Social Interaction but not Maternal Behavior

Adult-born neurons arrive to the olfactory bulb (OB) and integrate into the existing circuit throughout life. Despite the prevalence of this phenomenon, its functional impact is still poorly understood. Recent studies point to the importance of newly generated neurons to olfactory learning and memory. Adult neurogenesis is regulated by a variety of factors, notably by instances related to reproductive behavior, such as exposure to mating partners, pregnancy and lactation, and exposure to offspring. To study the contribution of olfactory neurogenesis to maternal behavior and social recognition, here we selectively disrupted OB neurogenesis using focal irradiation of the subventricular zone in adult female mice. We show that reduction of olfactory neurogenesis results in an abnormal social interaction pattern with male, but not female, conspecifics; we suggest that this effect could result from the inability to detect or discriminate male odors and could therefore have implications for the recognition of potential mating partners. Disruption of OB neurogenesis, however, neither impaired maternal-related behaviors, nor did it affect the ability of mothers to discriminate their own progeny from others.

Prefrontal nicotinic receptors control novel social interaction between mice

Social behavior is a defining mammalian feature that integrates emotional and motivational processes with external rewarding stimuli. It is thus an appropriate readout for complex behaviors, yet its neuronal and molecular bases remain poorly understood. In this study, we investigated the role of the mouse prefrontal area, particularly the involvement of β2‐subunit nicotinic receptors (β2∗‐nAChRs) in a paradigm of social behavior with concurrent motivations. We previously observed that mice lacking β2∗‐nAChRs (β2‐/‐) display increased time in social contact and exaggerated approach movements toward the novel conspecific. Here, combining behavioral analysis, localized brain lesions, and lentiviral gene rescue, we found that c‐Fos expression is specifically activated in the prelimbic (PrL) area of the prefrontal cortex (PFC) of mice exposed to a novel conspecific; lesions of the PrL area in wild‐type mice produce the same social pattern as in β2‐/‐ mice; and virally mediated reexpression of the β2‐subunit in the PrL area of β2‐/‐ mice rescues behavioral components in the social interaction task up to normal levels. Together, these data reveal that social interactions particularly mobilize the PrL area of the mouse PFC and that the presence of functional PrL β2∗‐nAChRs is necessary for this integrated behavior to emerge.—Avale, M. E., Chabout, J., Pons, S., Serreau, P., De Chauont, F., Olivo‐Marin, J‐C., Bourgeois, J‐P., Maskos, U., Changeux, J‐P., Granon, S. Prefrontal nicotinic receptors control novel social interaction between mice. FASEB J. 25, 2145‐2155 (2011). www.fasebj.org

Trisomy for Synaptojanin1 in Down syndrome is functionally linked to the enlargement of early endosomes

Enlarged early endosomes have been observed in neurons and fibroblasts in Down syndrome (DS). These endosome abnormalities have been implicated in the early development of Alzheimers disease (AD) pathology in these subjects. Here, we show the presence of enlarged endosomes in blood mononuclear cells and lymphoblastoid cell lines (LCLs) from individuals with DS using immunofluorescence and confocal microscopy. Genotype-phenotype correlations in LCLs carrying partial trisomies 21 revealed that triplication of a 2.56 Mb locus in 21q22.11 is associated with the endosomal abnormalities. This locus contains the gene encoding the phosphoinositide phosphatase synaptojanin 1 (SYNJ1), a key regulator of the signalling phospholipid phosphatidylinositol-4,5-biphosphate that has been shown to regulate clathrin-mediated endocytosis. We found that SYNJ1 transcripts are increased in LCLs from individuals with DS and that overexpression of SYNJ1 in a neuroblastoma cell line as well as in transgenic mice leads to enlarged endosomes. Moreover, the proportion of enlarged endosomes in fibroblasts from an individual with DS was reduced after silencing SYNJ1 expression with RNA interference. In LCLs carrying amyloid precursor protein (APP) microduplications causing autosomal dominant early-onset AD, enlarged endosomes were absent, suggesting that APP overexpression alone is not involved in the modification of early endosomes in this cell type. These findings provide new insights into the contribution of SYNJ1 overexpression to the endosomal changes observed in DS and suggest an attractive new target for rescuing endocytic dysfunction and lipid metabolism in DS and in AD.