Phosphoinositide-bis-phosphate is required for Saccharomyces cerevisiae invasive growth.

International audiencePhosphoinositide phosphates are important regulators of processes such as the cytoskeleton organization, membrane traffic and gene transcription, which are all critical for polarized cell growth. In particular PI(4,5)P2 plays essential roles in polarized growth as well as in cellular responses to stress. In the yeast Saccharomyces cerevisiae a sole PI(4)P-5-kinase, Mss4p is essential for generating plasma membrane PI(4,5)P2. Here we show that Mss4p is required for yeast invasive growth in low nutrient conditions. Specific mss4 mutants were isolated which are defective in cell elongation, induction of the Flo11p flocculin, adhesion and cell wall integrity. We show that mss4-f12 cells have reduced plasma membrane PI(4,5)P2 levels as well as a defect in the polarized distribution of this phospholipid, yet Mss4-f12p is catalytically active in vitro. In addition, the Mss4-f12 protein was defective in localizing to the plasma membrane. Furthermore, addition of cAMP, but not an activated MAPKKK allele, partially restored the invasive growth defect of mss4-f12 cells. Together our results indicate that plasma membrane PI(4,5)P2 is critical for yeast invasive growth and suggest that this phospholipid functions upstream of the cAMP-dependent protein kinase A signaling pathway

Machine-learning assisted phenotyping: From fungal morphology to mode of action hypothesis

International audienceBeyond growth inhibition, fungicides can also trigger specific morphological modifications visualized under transmitted light microscopy. These morphological changes result from the activity of a given compound via the inhibition of a molecular target, commonly named as its mode of action (MoA). We are hence able to classify different molecules into their respective MoA by observing their phenotypic signature, and even to detect new MoA with unknown phenotypic effect for further deconvolution. The aim of the presented work is to develop a robust method for automated recognition and classification of these phenotypic signatures in order to lead to a Mode of Action hypothesis. We compare two machine-learning methods (Random forest and Convolutional Neural Network) for direct processing of images generated on the grey mold Botrytis cinerea subjected to different antifungal molecules. © Bayer | Abteilung | Verfasser | Datu

How to define a rejection class based on model learning?

International audienceIn supervised classification, the learning process typically trains a classifier to optimize the accuracy of classifying data into the classes that appear in the learning set, and only them. While this framework fits many use cases, there are situations where the learning process is knowingly performed using a learning set that only represents the data that have been observed so far among a virtually unconstrained variety of possible samples. It is then crucial to define a classifier which has the ability to reject a sample, i.e., to classify it into a rejection class that has not been yet defined. Although obvious solutions can add this ability a posteriori to a classifier that has been learned classically, a better approach seems to directly account for this requirement in the classifier design. In this paper, we propose an innovative learning strategy for supervised classification that is able, by design, to reject a sample as not belonging to any of the known classes. For that, we rely on modeling each class as the combination of a probability density function (PDF) and a threshold that is computed with respect to the other classes. Several alternatives are proposed and compared in this framework. A comparison with straightforward approaches is also provided

A transgenic mouse expressing CHMP2B intron5 mutant in neurons develops histological and behavioural features of amyotrophic lateral sclerosis and frontotemporal dementia

International audienceMutations in the charged multivesicular body protein 2B (CHMP2B) are associated with frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and with a mixed ALS-FTD syndrome. To model this syndrome, we generated a transgenic mouse line expressing the human CHMP2Bintron5 mutant in a neuron-specific manner. These mice developed a dose-dependent disease phenotype. A longitudinal study revealed progressive gait abnormalities, reduced muscle strength and decreased motor coordination. CHMP2Bintron5 mice died due to generalized paralysis. When paralyzed, signs of denervation were present as attested by altered electromyographic profiles, by decreased number of fully innervated neuromuscular junctions, by reduction in size of motor endplates and by a decrease of sciatic nerve axons area. However, spinal motor neurons cell bodies were preserved until death. In addition to the motor dysfunctions, CHMP2Bintron5 mice progressively developed FTD-relevant behavioural modifications such as disinhibition, stereotypies, decrease in social interactions, compulsivity and change in dietary preferences. Furthermore, neurons in the affected spinal cord and brain regions showed accumulation of p62-positive cytoplasmic inclusions associated or not with ubiquitin and CHMP2Bintron5 As observed in FTD3 patients, these inclusions were negative for TDP-43 and FUS. Moreover, astrogliosis and microgliosis developed with age. Altogether, these data indicate that the neuronal expression of human CHMP2Bintron5 in areas involved in motor and cognitive functions induces progressive motor alterations associated with dementia symptoms and with histopathological hallmarks reminiscent of both ALS and FTD

CKIP-1 regulates mammalian and zebrafish myoblast fusion

Multinucleated muscle fibres arise by fusion of precursor cells called myoblasts. We previously showed that CKIP-1 ectopic expression in C2C12 myoblasts increased cell fusion. In this work, we report that CKIP-1 depletion drastically impairs C2C12 myoblast fusion in vitro and in vivo during zebrafish muscle development. Within developing fast-twich myotome, Ckip-1 localises at the periphery of fast precursor cells, closed to the plasma membrane. Unlike wild-type myoblasts that form spatially arrayed multinucleated fast myofibres, Ckip-1-deficient myoblasts show a drastic reduction in fusion capacity. A search for CKIP-1 binding partners identified the ARPC1 subunit of Arp2/3 actin nucleation complex essential for myoblast fusion. We demonstrate that CKIP-1, through binding to plasma membrane phosphoinositides via its PH domain, regulates cell morphology and lamellipodia formation by recruiting the Arp2/3 complex at the plasma membrane. These results establish CKIP-1 as a regulator of cortical actin that recruits the Arp2/3 complex at the plasma membrane essential for muscle precursor elongation and fusion