Nitrated α-Synuclein Induces the Loss of Dopaminergic Neurons in the Substantia Nigra of Rats

BACKGROUND: The pathology of Parkinson's disease (PD) is characterized by the degeneration of the nigrostriatal dopaminergic pathway, as well as the formation of intraneuronal inclusions known as Lewy bodies and Lewy neurites in the substantia nigra. Accumulations of nitrated alpha-synuclein are demonstrated in the signature inclusions of Parkinson's disease. However, whether the nitration of alpha-synuclein is relevant to the pathogenesis of PD is unknown. METHODOLOGY/PRINCIPAL FINDINGS: In this study, effect of nitrated alpha-synuclein to dopaminergic (DA) neurons was determined by delivering nitrated recombinant TAT-alpha-synuclein intracellular. We provide evidence to show that the nitrated alpha-synuclein was toxic to cultured dopaminergic SHSY-5Y neurons and primary mesencephalic DA neurons to a much greater degree than unnitrated alpha-synuclein. Moreover, we show that administration of nitrated alpha-synuclein to the substantia nigra pars compacta of rats caused severe reductions in the number of DA neurons therein, and led to the down-regulation of D(2)R in the striatum in vivo. Furthermore, when administered to the substantia nigra of rats, nitrated alpha-synuclein caused PD-like motor dysfunctions, such as reduced locomotion and motor asymmetry, however unmodified alpha-synuclein had significantly less severe behavioral effects. CONCLUSIONS/SIGNIFICANCE: Our results provide evidence that alpha-synuclein, principally in its nitrated form, induce DA neuron death and may be a major factor in the etiology of PD

Symbiont dynamics during the blood meal of Ixodes ricinus nymphs differ according to their sex

Ticks harbour rich and diverse microbiota and, among the microorganisms associated with them, endosymbionts are the subject of a growing interest due to their crucial role in the biology of their arthropod host. Midichloria mitochondrii is the main endosymbiont of the European tick Ixodes ricinus and is found in abundance in all I. ricinus females, while at a much lower density in males, where it is even absent in 56 % of the individuals. This endosymbiont is also known to increase in numbers after the blood meal of larvae, nymphs or females. Because of this difference in the prevalence of M. mitochondrii between the two sexes, surveying the density of these bacteria in nymphs that will become either females or males could help to understand the behaviour of Midichloria in its arthropod host. To this aim, we have set up an experimental design by building 3 groups of unfed nymphs based on their scutum and hypostome lengths. After engorgement, weighing and moulting of a subset of the nymphs, a significant difference in sex-ratio among the 3 groups was observed. In parallel, Midichloria load in individual nymphs was quantified by qPCR both before and after engorgement. No difference in either body mass or Midichloria load was observed at the unfed stage, but following engorgement, both features were significantly different between each size group. Our results demonstrate that symbiont dynamics during nymphal engorgement is different between the two sexes, resulting in a significantly higher Midichloria load in nymphs that will become females. The consequences of those findings on our understanding of the interplay between the endosymbiont and its arthropod host are discussed

Sequence diversity and evolution of a group of iflaviruses associated with ticks

We studied a group of tick-associated viruses with characteristics of members of the family Iflaviridae, a family of viruses frequently found in arthropods. Our aim was to gain insight into the evolutionary dynamics of this group of viruses, which may be linked to the biology of ticks. We explored assembled RNA-Seq data sets for different species of ticks. We identified members of five different iflavirus species, four of them novel, and discovered nine new genome sequences, including variants. Five variants represented a virus species associated with Ixodes ricinus. Unexpectedly, a sequence found in the Ixodes scapularis cell line ISE6 was nearly identical to the sequences of I. ricinus variants, suggesting a contamination of this cell line by I. ricinus material. Analysing patterns of substitutions between these variants, we detected a strong excess of synonymous mutations, suggesting evolution under strong positive selection. The phylogenies of the viruses and of their tick hosts were not congruent, suggesting recurrent host changes across tick genera during their evolution. Overall, our work constitutes a step in the understanding of the interactions between this family of viruses and ticks

Digging deep into intramitochondrial symbiosis: dual transcriptomics of the hard tick Ixodes ricinus and its bacterial symbiont Midichloria mitochondrii

INTRODUCTION. Ixodes ricinus is a hard tick, widespread in Europe and in the Mediterranean basin, that can act as vector of multiple diseases of human and veterinary importance. Midichloria mitochondrii is a bacterial symbiont of this tick, capable of living in the intermembrane space of mitochondria (Beninati et al., 2004, Appl. Environ. Microbiol., 70:2596\u20132602). The bacterium was found to be present in most tick individuals (Lo et al., 2006, Environ. Microbiol., 8:1280-1287) and to be vertically transmitted to the progeny (Sassera et al., 2008, Appl. Environ. Microbiol., 74:6138-6140). To investigate the relationship between host and symbiont we designed an ad-hoc protocol of dual RNA-Seq to sequence the transcriptomes of both organisms in different phases of tick engorgement. MATERIALS AND METHODS. Ticks were collected on roe deer, cut in half and stored in RNALater on site, in order to freeze the transcription patterns in each stage. Ticks were dissected in RNALater and total RNA was extracted from ovaries and salivary glands. A custom library construction kit was designed and used in order to preserve transcripts from both organisms and to limit the prevalence of rRNA sequences in the sample (normally over 85%). The kit protocol included the use of custom designed probes for rRNA depletion. Libraries were sequenced on Illumina machines and the resulting reads were assembled to obtain a reference transcriptome to be used for downstream analyses. RESULTS AND CONCLUSIONS. Ticks were subjected to a custom protocol for RNA sequencing which allowed to obtain an average of 40 million reads per sample and over 50% of the reads were transcripts of host or symbiont. After assembly, over 18,000 tick transcripts and over 1,200 bacterial transcripts were obtained. Differential expression analysis will be performed in the upcoming months; so far, the main result of this work is the development of a sound protocol for dual RNA-seq in this system

Ixodes frontalis, une espèce de tique fréquente et facile à collecter au drap ou au drapeau quand on sait où la chercher!

Parmi la quarantaine d\u2019esp\ue8ces de tiques pr\ue9sente en France ou la soixantaine dans l\u2019ouest pal\ue9artique, la distribution d\u2019Ixodes frontalis demeure mal connue bien qu\u2019elle semble largement r\ue9pandue. L\u2019immense majorit\ue9 des donn\ue9es disponibles dans la litt\ue9rature pour cette esp\ue8ce est issue de collectes sur oiseaux (notamment des passereaux). Dans le cadre de 2 programmes de recherche cons\ue9cutifs (CC-EID puis CLIMATICK, m\ue9taprogramme INRA \uabACCAF \ubb), l\u2019un des 8 sites du r\ue9seau o\uf9 la dynamique des populations d\u2019Ixodes ricinus est \ue9tudi\ue9e a montr\ue9 une forte abondance de larves d\u2019Ixodes frontalis collect\ue9es sur la liti\ue8re par la m\ue9thode du drap (Agoulon et al. 2019). Comme cette esp\ue8ce \ue9tait fortement concentr\ue9e au niveau des quelques transects entour\ue9s de bambous, nous avons cherch\ue9 \ue0 savoir si cette situation \ue9tait g\ue9n\ue9ralisable \ue0 d\u2019autres localit\ue9s. Une recherche syst\ue9matique dans les parcs de la ville de Nantes o\uf9 des bambous sont pr\ue9sents nous a permis de trouver l\u2019esp\ue8ce dans X cas sur Y. Nous avons ensuite \ue9tendu cette recherche dans X autres villes en France et en Italie o\uf9 elle a \ue9t\ue9 trouv\ue9e dans Y cas sur Z. Cette esp\ue8ce m\ue9connue est donc finalement relativement facile \ue0 trouver par la m\ue9thode du drap ou du drapeau si on la cherche sous des bambous. Nous faisons l\u2019hypoth\ue8se que les bosquets de cette gramin\ue9e introduite constituent des sites privil\ue9gi\ue9s pour constituer des dortoirs nocturnes pour les passereaux. Cette esp\ue8ce \ue9tant connue comme h\ue9bergeant des pathog\ue8nes zoonotiques, les cons\ue9quences de cette d\ue9couverte pour l\u2019\ue9pid\ue9miologie des maladies \ue0 tiques seront discut\ue9es

Correction: Transcriptome of the synganglion in the tick Ixodes ricinus and evolution of the cys-loop ligand-gated ion channel family in ticks

International audienc

Transcriptome of the synganglion in the tick Ixodes ricinus and evolution of the cys-loop ligand-gated ion channel family in ticks

International audienceBackground: Ticks represent a major health issue for humans and domesticated animals. Exploring the expression landscape of the tick’s central nervous system (CNS), known as the synganglion, would be an important step in understanding tick physiology and in managing tick-borne diseases, but studies on that topic are still relatively scarce. Neuron-specific genes like the cys-loop ligand-gated ion channels (cys-loop LGICs, or cysLGICs) are important pharmacological targets of acaricides. To date their sequence have not been well catalogued for ticks, and their phylogeny has not been fully studied. Results: We carried out the sequencing of transcriptomes of the I. ricinus synganglion, for adult ticks in different conditions (unfed males, unfed females, and partially-fed females). The de novo assembly of these transcriptomes allowed us to obtain a large collection of cys-loop LGICs sequences. A reference meta-transcriptome based on synganglion and whole body transcriptomes was then produced, showing high completeness and allowing differential expression analyses between synganglion and whole body. Many of the genes upregulated in the synganglion were associated with neurotransmission and/or localized in neurons or the synaptic membrane. As the first step of a functional study of cysLGICs, we cloned the predicted sequence of the resistance to dieldrin (RDL) subunit homolog, and functionally reconstituted the first GABA-gated receptor of Ixodes ricinus . A phylogenetic study was performed for the nicotinic acetylcholine receptors (nAChRs) and other cys-loop LGICs respectively, revealing tick-specific expansions of some types of receptors (especially for Histamine-like subunits and GluCls). Conclusions: We established a large catalogue of genes preferentially expressed in the tick CNS, including the cysLGICs. We discovered tick-specific gene family expansion of some types of cysLGIC receptors, and a case of intragenic duplication, suggesting a complex pattern of gene expression among different copies or different alternative transcripts of tick neuro-receptors