Nutrition and colony investment in Solenopsis invicta workers

Dissertação de Mestrado em Biologia Celular e Molecular, apresentada ao Departamento de Ciências da Vida Da Faculdade de Ciências e Tecnologia da Universidade de Coimbra.A proteína Tau é responsável pela ligação e estabilização dos microtúbulos (MT) no citoesqueleto, sendo fundamental na função neuronal. A atividade desta proteína pode ser regulada por modificações pós-translacionais, como a fosforilação, que promovem a separação dos microtúbulos. A alteração na conformação da Tau provocada por uma deficiente regulação, como a híper-fosforilação, causa destabilização dos MT e agregação da mesma em filamentos helicoidais emparelhados e tranças neurofibrilares. Estas estruturas são uma das principais características na doença de Alzheimer (AD), e o seu processo de formação pode representar um dos principais motivos que leva a morte celular nas Tauopatias, inclusivamente AD e outras patologias neurodegenerativas. Nos últimos anos, recursos têm sido empregues na descoberta de novas estratégias que permitam diminuir a formação ou diminuam a quantidade de agregados da Tau dentro das células. Estudos recentes identificaram a indução da autofagia através da rapamicina como um dos potenciais alvos no aumento da remoção de agregados proteicos associados a doenças neurodegenerativas, melhorando também a esperança de vida em ratos e outros modelos. Recentemente, o nosso laboratório desenvolveu um modelo celular baseado no trabalho de Guo e Lee (2011) que mimetiza a agregação intracelular da Tau depois de induzida a expressão de uma forma mutada desta proteína seguido do seeding com fibrilas K18:P301L pré-agregadas. Neste estudo, foi possível demonstrar como a utilização destes modelos permite identificar novos compostos com atividade nas vias de redução da Tau. Curiosamente estas moléculas foram responsáveis pelo desenvolvimento de um fenótipo vesicular que identificámos como sendo lisossomas, derivados de um possível estímulo na via endócitica. As alterações na morfologia sub-celular foram acompanhadas por modificações em marcadores de autofagia, sem aumento no fluxo autofágico. Estes dados sugerem que o aumento na degradação de proteínas e estruturas por autofagia poderão ter origem em efeitos colaterais de outras vias em detrimento do estímulo direto. Para além disso, testamos uma série de moléculas com atividade reconhecida e validadas para induzir autofagia ou bloquear a degradação no lisossoma. Foi demonstrado que no nosso modelo, a ativação da autofagia não é responsável pela remoção de agregados. Por outro lado, provámos que os lisossomas são extremamente importantes da degradação de agregados da Tau. Por fim, usámos o fator de transcrição EB (TFEB) para aumentar a biogénese de lisossomas e a autofagia. Células transfectadas com este fator apresentaram menos agregados de Tau e um aumento na viabilidade celular. Quando considerados em conjunto, estes resultados demonstram que a biogénese de lisossomas seguida por estímulos na autofagia podem ser mais importantes do que a ativação da autofagia por si só. Concluindo, com este projeto foi não só possível identificar os mecanismos dos compostos responsáveis pela degradação dos agregados de Tau, como também foi possível validar o TFEB como um potencial novo alvo na descoberta de novos fármacos.Tau protein is responsible for binding and stabilizing microtubules (MT) in the cytoskeleton, thus supporting neuronal function. This protein activity can be regulated by post-translation modifications, such as phosphorylation, which promotes MT detachment. Tau misfolding provoked by abnormal regulation, like hyperphosphorilation, causes MT destabilization and Tau aggregation into paired helical filaments (PHF) and neurofibrillary tangles (NFTs). These structures are one of the main hallmarks in Alzheimer’s disease (AD), and its formation process may represent the principal motive for cell death in many Tauopathies, including AD and other neurodegenerative disorders. Over the last years, great efforts have been placed to find new strategies to either diminish the build-up or decrease the amount of aggregated Tau inside cells. Recent studies have identified induction of autophagy through rapamycin as a potential target in increasing the clearance of aggregated proteins associated with neurodegenerative diseases, as well as ameliorating life expectancy in rats and other animal models. Recently, our lab developed a cellular model based on the work by Guo and Lee (2011) that mimics the intracellular aggregation of Tau after overexpression of a mutated form of this protein and seeding with pre-aggregated K18:P301L fibrils. In this study, we have taken advantage of the developed model to discover new compounds active in Tau reduction pathways. Interestingly these molecules were responsible for the development of a vesicular phenotype that we identified as lysosomes due to a possible stimulation of the endocytic pathway. The change of the sub cellular morphology was followed by changes in autophagy markers, with no increase in the autophagic flux. This suggests an increment in the degradation of proteins and structures by autophagy as a collateral result from the activation of other pathways rather than a direct stimulus. Furthermore, we have tested a series of molecules with known and validated activity to induce autophagy or disable degradation via the lysosome. We showed that at least in our model, autophagy activation is not responsible for the clearance of aggregates. On the other hand, we have proven that lysosomes play a critical role in Tau aggregates degradation. Finally, we have used the transcription factor EB (TFEB) to intensify lysosomal biogenesis and autophagy. Cells transfected with this transcription factor had less Tau aggregates and cell viability was slightly increased. When considered together, these results show that lysosomal biogenesis followed by autophagy stimulation may be more important for clearance of Tau aggregates than autophagy by itself. In conclusion, we have not only determined the mechanisms targeted by the compounds responsible for the degradation of Tau aggregates, but also validated TFEB as a potential new target for drug discovery

Deciphering the Chemical Basis of Nestmate Recognition

Social insects maintain colony cohesion by recognizing and, if necessary, discriminating against conspecifics that are not part of the colony. This recognition ability is encoded by a complex mixture of cuticular hydrocarbons (CHCs), although it is largely unclear how social insects interpret such a multifaceted signal. CHC profiles often contain several series of homologous hydrocarbons, possessing the same methyl branch position but differing in chain length (e.g., 15-methyl-pentatriacontane, 15-methyl-heptatriacontane, 15-methyl-nonatriacontane). Recent studies have revealed that within species these homologs can occur in correlated concentrations. In such cases, single compounds may convey the same information as the homologs. In this study, we used behavioral bioassays to explore how social insects perceive and interpret different hydrocarbons. We tested the aggressive response of Argentine ants, Linepithema humile, toward nest-mate CHC profiles that were augmented with one of eight synthetic hydrocarbons that differed in branch position, chain length, or both. We found that Argentine ants showed similar levels of aggression toward nest-mate CHC profiles augmented with compounds that had the same branch position but differed in chain length. Conversely, Argentine ants displayed different levels of aggression toward nest-mate CHC profiles augmented with compounds that had different branch positions but the same chain length. While this was true in almost all cases, one CHC we tested elicited a greater aggressive response than its homologs. Interestingly, this was the only compound that did not occur naturally in correlated concentrations with its homologs in CHC profiles. Combined, these data suggest that CHCs of a homologous series elicit the same aggressive response because they convey the same information, rather than Argentine ants being unable to discriminate between different homologs. This study contributes to our understanding of the chemical basis of nestmate recognition by showing that, similar to spoken language, the chemical language of social insects contains “synonyms,” chemicals that differ in structure, but not meaning

Inferring introduction routes of invasive species using approximate Bayesian computation on microsatellite data

Determining the routes of introduction provides not only information about the history of an invasion process, but also information about the origin and construction of the genetic composition of the invading population. It remains difficult, however, to infer introduction routes from molecular data because of a lack of appropriate methods. We evaluate here the use of an approximate Bayesian computation (ABC) method for estimating the probabilities of introduction routes of invasive populations based on microsatellite data. We considered the crucial case of a single source population from which two invasive populations originated either serially from a single introduction event or from two independent introduction events. Using simulated datasets, we found that the method gave correct inferences and was robust to many erroneous beliefs. The method was also more efficient than traditional methods based on raw values of statistics such as assignment likelihood or pairwise F(ST). We illustrate some of the features of our ABC method, using real microsatellite datasets obtained for invasive populations of the western corn rootworm, Diabrotica virgifera virgifera. Most computations were performed with the DIYABC program (http://www1.montpellier.inra.fr/CBGP/diyabc/)

Electronic Coherence Dephasing in Excitonic Molecular Complexes: Role of Markov and Secular Approximations

We compare four different types of equations of motion for reduced density matrix of a system of molecular excitons interacting with thermodynamic bath. All four equations are of second order in the linear system-bath interaction Hamiltonian, with different approximations applied in their derivation. In particular we compare time-nonlocal equations obtained from so-called Nakajima-Zwanzig identity and the time-local equations resulting from the partial ordering prescription of the cummulant expansion. In each of these equations we alternatively apply secular approximation to decouple population and coherence dynamics from each other. We focus on the dynamics of intraband electronic coherences of the excitonic system which can be traced by coherent two-dimensional spectroscopy. We discuss the applicability of the four relaxation theories to simulations of population and coherence dynamics, and identify features of the two-dimensional coherent spectrum that allow us to distinguish time-nonlocal effects.Comment: 14 pages, 8 figure

Inselect: Automating the Digitization of Natural History Collections

Copyright: © 2015 Hudson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

A new multicompartmental reaction-diffusion modeling method links transient membrane attachment of E. coli MinE to E-ring formation

Many important cellular processes are regulated by reaction-diffusion (RD) of molecules that takes place both in the cytoplasm and on the membrane. To model and analyze such multicompartmental processes, we developed a lattice-based Monte Carlo method, Spatiocyte that supports RD in volume and surface compartments at single molecule resolution. Stochasticity in RD and the excluded volume effect brought by intracellular molecular crowding, both of which can significantly affect RD and thus, cellular processes, are also supported. We verified the method by comparing simulation results of diffusion, irreversible and reversible reactions with the predicted analytical and best available numerical solutions. Moreover, to directly compare the localization patterns of molecules in fluorescence microscopy images with simulation, we devised a visualization method that mimics the microphotography process by showing the trajectory of simulated molecules averaged according to the camera exposure time. In the rod-shaped bacterium _Escherichia coli_, the division site is suppressed at the cell poles by periodic pole-to-pole oscillations of the Min proteins (MinC, MinD and MinE) arising from carefully orchestrated RD in both cytoplasm and membrane compartments. Using Spatiocyte we could model and reproduce the _in vivo_ MinDE localization dynamics by accounting for the established properties of MinE. Our results suggest that the MinE ring, which is essential in preventing polar septation, is largely composed of MinE that is transiently attached to the membrane independently after recruited by MinD. Overall, Spatiocyte allows simulation and visualization of complex spatial and reaction-diffusion mediated cellular processes in volumes and surfaces. As we showed, it can potentially provide mechanistic insights otherwise difficult to obtain experimentally

A New (Old), Invasive Ant in the Hardwood Forests of Eastern North America and Its Potentially Widespread Impacts

Biological invasions represent a serious threat for the conservation of biodiversity in many ecosystems. While many social insect species and in particular ant species have been introduced outside their native ranges, few species have been successful at invading temperate forests. In this study, we document for the first time the relationship between the abundance of the introduced ant, Pachycondyla chinensis, in mature forests of North Carolina and the composition, abundance and diversity of native ant species using both a matched pair approach and generalized linear models. Where present, P. chinensis was more abundant than all native species combined. The diversity and abundance of native ants in general and many individual species were negatively associated with the presence and abundance of P. chinensis. These patterns held regardless of our statistical approach and across spatial scales. Interestingly, while the majority of ant species was strongly and negatively correlated with the abundance and presence of P. chinensis, a small subset of ant species larger than P. chinensis was either as abundant or even more abundant in invaded than in uninvaded sites. The large geographic range of this ant species combined with its apparent impact on native species make it likely to have cascading consequences on eastern forests in years to come, effects mediated by the specifics of its life history which is very different from those of other invasive ants. The apparent ecological impacts of P. chinensis are in addition to public health concerns associated with this species due to its sometimes, deadly sting

Widespread range expansions shape latitudinal variation in insect thermal limits

I thank the authors of previous studies on global variation in insect thermal tolerances who have generously provided open access use of their data sets.Peer reviewedPostprin