Complementary Roles of the Hippocampus and the Dorsomedial Striatum during Spatial and Sequence-Based Navigation Behavior

We investigated the neural bases of navigation based on spatial or sequential egocentric representation during the completion of the starmaze, a complex goal-directed navigation task. In this maze, mice had to swim along a path composed of three choice points to find a hidden platform. As reported previously, this task can be solved by using two hippocampal-dependent strategies encoded in parallel i) the allocentric strategy requiring encoding of the contextual information, and ii) the sequential egocentric strategy requiring temporal encoding of a sequence of successive body movements associated to specific choice points. Mice were trained during one day and tested the following day in a single probe trial to reveal which of the two strategies was spontaneously preferred by each animal. Imaging of the activity-dependent gene c-fos revealed that both strategies are supported by an overlapping network involving the dorsal hippocampus, the dorsomedial striatum (DMS) and the medial prefrontal cortex. A significant higher activation of the ventral CA1 subregion was observed when mice used the sequential egocentric strategy. To investigate the potential different roles of the dorsal hippocampus and the DMS in both types of navigation, we performed region-specific excitotoxic lesions of each of these two structures. Dorsal hippocampus lesioned mice were unable to optimally learn the sequence but improved their performances by developing a serial strategy instead. DMS lesioned mice were severely impaired, failing to learn the task. Our data support the view that the hippocampus organizes information into a spatio-temporal representation, which can then be used by the DMS to perform goal-directed navigation.     

Deep-sea squat lobster biogeography (Munidopsidae: Leiogalathea) unveils Tethyan vicariance and evolutionary patterns shared by shallow-water relatives

The ecology, abundance and diversity of galatheoid squat lobsters make them an ideal group to study deep-sea diversification processes. Here, we reconstructed the evolutionary and biogeographic history of Leiogalathea, a genus of circum-tropical deep-sea squat lobsters, in order to compare patterns and processes that have affected shallow-water and deep-sea squat lobster species. We first built a multilocus phylogeny and a calibrated species tree with a relaxed clock using StarBEAST2 to reconstruct evolutionary relationships and divergence times among Leiogalathea species. We used BioGeoBEARS and a DEC model, implemented in RevBayes, to reconstruct ancestral distribution ranges and the biogeographic history of the genus. Our results showed that Leiogalathea is monophyletic and comprises four main lineages; morphological homogeneity is common within and between clades, except in one; the reconstructed ancestral range of the genus is in the Atlantic and Indian oceans (Tethys). They also revealed the divergence of the Atlantic species around 25 million years ago (Ma), intense cladogenesis 15–25 Ma and low levels of speciation over the last 5 million years (Myr). The four Leiogalathea lineages showed similar patterns of speciation: allopatric speciation followed by range expansion and subsequent stasis. Leiogalathea started diversifying during the Oligocene, likely in the Tethyan. The Atlantic lineage then split from its Indo-Pacific sister group due to vicariance driven by closure of the Tethys Seaway. The Atlantic lineage is less speciose compared with the Indo-Pacific lineages, with the Tropical Southwestern Pacific being the current centre of diversity. Leiogalathea diversification coincided with cladogenetic peaks in shallow-water genera, indicating that historical biogeographic events similarly shaped the diversification and distribution of both deep-sea and shallow-water squat lobsters.     

Increased membrane immunoglobulin capping of B cells from C57Bl/6 lpr/lpr and C57Bl/6 nu/nu mice

When the capping of membrane immunoglobulin on spleen B cells from normal C57Bl/6 mice (B6) is taken as reference, a faster capping rate is found for cells of age-matched B6 mice which are congenic at the lymphoproliferation (lpr) or nude (nu) loci. Though both congenic strains can be characterized by an abnormal T-lineage cell content, the nature of the abnormality itself is very different since B6 nudes lack thymus-processed/influenced lymphocytes whereas B6 mice with the lpr phenotype suffer from an invasion of all lymphoid organs with cells of a particular T-cell subset. Moreover, the more "normal" capping rate of B cells from the double congenic B6 mice (nu/nu, lpr/lpr) is intriguing. Since other mice homozygous at the lpr locus (MRL-1) or at the nu locus (BALB/c nude) also cap faster than their congenic controls (MRL-n and BALB/c, respectively), the observed effects do not appear to depend on a peculiarity of the B6 genetic background. If the faster capping of B cells of nu congenic and of lpr congenic mice had a common origin, it might be that T cells would control in some way the mobility of B-cell membrane immunoglobulins: both congenic mice have in their spleen a very low proportion of mature T cells together with a very high proportion of prethymic/thymic immature T-cell types, either of which might affect B-cell behavioral responses to membrane immunoglobulin clustering.     

A fluorescent hydrophobic probe used for monitoring the kinetics of exocytosis phenomena

A fluorescence method is presented for quantitatively analyzing exocytosis phenomena and monitoring their kinetics. The method is based on the particular properties of a hydrophobic fluorescent probe, 1-[4-(trimethylammonio)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH) [Prendergast, F.G., Haugland, R.P., & Callahan, P.J. (1981) Biochemistry 20, 7333-7338; Kuhry, J.G., Fonteneau, P., Duportail, G., Maechling, C., & Laustriat, G. (1983) Cell Biophys. 5, 129-140; Kuhry, J.G., Duportail, G., Bronner, C., & Laustriat, G. (1985) Biochim. Biophys. Acta 845, 60-67]. When this probe is interacted with intact resting cells in aqueous suspensions, it labels solely the membranes that are in contact with the external medium and is incorporated into them according to a partition equilibrium; i.e., the amount of the probe incorporated is proportional to the available membrane surface. TMA-DPH is highly fluorescent in membranes and not at all in water. Thus, a measurement of the TMA-DPH fluorescence intensity provides a signal proportional to the membrane surface. In secretory cells, the membrane surface available for the probe is increased upon fusion of the membrane of the secretory granules with the cell plasma membranes, directly or via intergranule fusion. Thus, when these cells are stimulated, more TMA-DPH is incorporated than in resting cells since the probe is allowed to also interact with the granule membranes now connected with the external medium by pores. This process results in a proportional increase in the TMA-DPH fluorescence intensity. The response was found to be very rapid and able to follow accurately the exocytosis kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

Bioguided Fractionation and Isolation of an Antiplasmodial Saponin from the Roots of Nauclea xanthoxylon (A.Chev.) Aubrév. (Rubiaceae)

The root extract of Nauclea xanthoxylon (A.Chev.) Aubrév. displayed significant 50 % inhibition concentration (IC₅₀s) of 0.57 and 1.26 μg/mL against chloroquine resistant and sensitive Plasmodium falciparum (Pf) Dd2 and 3D7 strains, respectively. Bio-guided fractionation led to an ethyl acetate fraction with IC₅₀s of 2.68 and 1.85 μg/mL and subsequently, to the new quinovic acid saponin named xanthoxyloside ( 1 ) with IC₅₀s of 0.33 and 1.30 μM, respectively against the tested strains. Further compounds obtained from ethyl acetate and hexane fractions were the known clethric acid ( 2 ), ursolic acid ( 3 ), quafrinoic acid ( 4 ), quinovic acid ( 5 ), quinovic acid 3-O-β-D-fucopyranoside ( 6 ), oleanolic acid ( 7 ), oleanolic acid 3-acetate ( 8 ), friedelin ( 9 ), β-sitosterol ( 10a ), stigmasterol ( 10b ) and stigmasterol 3-O-β-D-glucopyranoside ( 11 ). Their structures were characterised with the aid of comprehensive spectroscopic methods (1 and 2D NMR, Mass). Bio-assays were performed using nucleic acid gel stain (SYBR green I)-based fluorescence assay with chloroquine as reference. Extracts and compounds exhibited good selectivity indices (SIs) of >10. Significant antiplasmodial activities measured for the crude extract, the ethyl acetate fraction and xanthoxyloside ( 1 ) from that fraction can justify the use of the root of N. xanthoxylon in ethnomedicine to treat malaria.     

Production of acetylcholine receptors from TE671 cells grown on microcarriers

Summary When grown in DMEM supplemented with 10 % fetal calf serum and using Cytodex 3® as microcarriers, TE671 cells entering the stationary phase optimally expressed acetylcholine receptors. These, receptors could be conveniently extracted from cell-saturated, microbeads or monodispersed cells obtained by trypsinization of microbeads. Typically, a 500 ml-batch gave 6–7 pmol of receptors which could be used as antigen to assay anti-acetylcholine receptor antibodies in the sera of myasthenic patients.     

Internalization of the lipophilic fluorescent probe trimethylamino-diphenylhexatriene follows the endocytosis and recycling of the plasma membrane in cells

The lipophilic fluorescent probe trimethylamino-diphenylhexatriene (TMA-DPH) has been shown previously to behave as a marker of plasma membrane in living cell systems, and it has therefore been widely used in membrane fluidity studies via fluorescence anisotropy measurements. However, progressive internalization of this probe in cells could lead to unsuitable interferences, when long incubations times were required. The mechanism of this internalization had not yet been elucidated. We present here fluorescence-intensity kinetic results and fluorescence micrographic data on L929 cells and on mouse bone-marrow macrophages, which allow us to identify the mechanism as fluid-phase pinocytosis: the probe remains associated with the plasma membrane throughout its internalization-recycling flow and it is finally concentrated in lysosomes. The study was facilitated by the partition equilibrium property of TMA-DPH between plasma membranes and the external aqueous medium, which allowed to immediately distinguish the internalized fraction of the probe from the peripheral labelling, by simply washing cells. This conclusion is confirmed by the features of the influence of temperature on TMA-DPH internalization.     

Older than New Caledonia emergence? A molecular phylogenetic study of the eneopterine crickets (Orthoptera: Grylloidea)

Aim A New Caledonian insect group was studied in a world‐wide phylogenetic context to test: (1) whether local or regional island clades are older than 37 Ma, the postulated re‐emergence time of New Caledonia; (2) whether these clades show evidence for local radiations or multiple colonizations; and (3) whether there is evidence for relict taxa with long branches in phylogenetic trees that relate New Caledonian species to geographically distant taxa. Location New Caledonia, south‐west Pacific. Methods We sampled 43 cricket species representing all tribes of the subfamily Eneopterinae and 15 of the 17 described genera, focusing on taxa distributed in the South Pacific and around New Caledonia. One nuclear and three mitochondrial genes were analysed using Bayesian and parsimony methods. Phylogenetic divergence times were estimated using a relaxed clock method and several calibration criteria. Results The analyses indicate that, under the most conservative dating scenario, New Caledonian eneopterines are 5–16 million years old. The largest group in the Pacific region dates to 18–29 Ma. New Caledonia has been colonized in two phases: the first around 10.6 Ma, with the subsequent diversification of the endemic genus Agnotecous, and the second with more recent events around 1–4 Ma. The distribution of the sister group of Agnotecous and the lack of phylogenetic long branches in the genus refute an assumption of major extinction events in this clade and the hypothesis of local relicts. Main conclusions Our phylogenetic studies invalidate a simple scenario of local persistence of this group in New Caledonia since 80 Ma, either by survival on the New Caledonian island since its rift from Australia, or, if one accepts the submergence of New Caledonia, by local island‐hopping among other subaerial islands, now drowned, in the region during periods of New Caledonian submergence.     

Molecular Epidemiology of Carbapenem Non-Susceptible Acinetobacter baumannii in France

Carbapenem-resistant Acinetobacter baumannii have emerged globally. The objective of this study was to investigate the epidemiology, clonal diversity and resistance mechanisms of imipenem non-susceptible A. baumannii isolates in France. Between December 2010 and August 2011, 132 notifications were collected, including 37 outbreaks corresponding to 242 cases (2 to 55 per cluster). Multilocus sequence typing, pulsed-field gel electrophoresis (PFGE) and characterisation of carbapenemase-encoding genes were performed on 110 non-repetitive isolates. Gene bla _OXA-23 was the most frequently detected (82%), followed by bla _OXA-24 (11%) and bla _OXA-58 (7%). Eleven sequence types (ST) were distinguished, among which sequence types ST1, ST2 (64%), ST20, ST25, ST85 and ST107. Isolates from epidemiological clusters had the same ST and resistance genes, indicating probable transmission within centres. In contrast, PFGE types of isolates differed among centres, arguing against transmission among centers. This study provides the first epidemiological snapshot of the population of A. baumannii with reduced susceptibility to carbapenems from France, and further underlines the predominance of international clones.