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Drosophila melanogaster come modello per lo studio delle encefalopatie spongiformi trasmissibili umane di tipo ereditario
Full text linkPrion diseases, or trasmissible spongiform encephalopathies (TSEs), are a group of fatal neurodegenerative diseases that affect humans and other mammalians. All these pathologies have long incubation periods followed by a crhonic neurological disease with fatal outcomes and have similar pathology limited to the central nervous system. TSEs are characterized hystopathologically by spongiosis and neural loss.
The infectious agent in prion diseases is believed to be represented by a single protein, named prion protein (PrPC). The “Protein Only Hypothesis” [1] suggests that TSE are caused by a disease-associated and improperly folded form of PrPC, termed PrPSc. The nature of prions and the mechanism by which they propagate still poses fascinating basic questions.
Human TSEs are biologically unique in that the disease process can be triggered by different phenomena: i) infection with prion infected tissues, such as kuru and the new variant of Creuzfeldt-Jacob disease (vCJD); ii) a sporadic event that generates PrPSc, for example in CJD, and iii) inherited mutations in the human prion protein encoding gene PRNP, which cause fatal familial insomnia (FFI), Gerstmann-Straussler-Scheinker disease (GSS) and familial CJD.
The extraordinary structural and functional conservation of genes and pathways observed in distantly related organisms, from yeast to primates, has made possible to use model organisms to further our understanding of human biology. Several studies performed using transgenic animal models have yeld a wealth of new knowledge about infectious, genetic and sporadic prion diseases.
The aim of this work is to investigate human inherited prion diseases (IPDs) thus helping to advance our knowledge of molecular mechanism responsible of these pathologies that are presently not understood, using a Drosophila melanogaster animal model.
Among invertebrate model organisms, Drosophila presents the highest degree of gene conservation to humans and, importantly, it has an high evolved nervous system. The fly brain is estimated to have more than 300,000 neurons and, similarly to mammals, is organised into areas with separated specialised functions. In addition, the fruit fly offers a number of experimental advantages, including short lifespan, well characterized development and anatomy, sequenced genome and simple transgenic analysis. Several studies indicate that not only basic cell biology but also higher-order events such as organs construction and function have been conserved between human and flies throughout the evolution. Moreover, an unparallel advantage of invertebrates is the ability to carry out large-scale genetic screens rapidly. Finally, Drosophila has an unrivalled battery of genetic tools including rapidly expanding collections of mutants, trasposon-based methods for gene manipulation, systems that allow controlled ectopic gene expression and balancer chromosomes. These attributes, along with the rapid generation time, inexpensive culture requirements and large progeny numbers produced in a single cross, make Drosophila an incisive tool for the analysis of
human diseases.
Therefore, we generated transgenic fruit flies for constructs carryng either wild type or mutated forms of human PrP (H-PrP). In particular, the mutations were: P102L, associated to GSS syndrome; D178N/129M associated to FFI; D178N/129V and E200K both associated to fCJD. With standard genetic crosses, the different human PrP forms were actively expressed in all tissues, in the entire nervous system, or in motor neurons. Flies expressing H-PrP exhibited severe age-dependent locomotor dysfunction and premature death. These flies showed a progressive loss of the ability to fly, followed by a progressive loss of the capability to walk on the tubes where they are collected: they did not fly, walked slowly, had difficulty righting themselves when they are knocked down. Moreover, they lost the control of their leg movements: leg quivered and the flies often fell on a side, like they missed the support of the legs. At the same time, they showed an altered movement of wings and antennae as they continuously groomed themselves. Locomotor activities were analyzed by specific behavioural tests and evaluating possible alteration in neuromuscolar junctions.
Moreover, in order to evaluate the presence of tissue vacuolization/spongiosis and/or PrPSc deposition, adult flies brains were examined by standard hematoxiyin/eosin stained sections at different time points. In particular, we analized brain sections when flies display severe age-dependent behavioural alterations.
Our findings indicate that Drosophila could be a powerful tool to study human familial TSEs. In particular, H-PrP expression in transgenic flies gives rise to gross behavioural phenotypes that closely remind the neurodegeneration associated with altered function of prion diseases in humans.
While knowledge of the precise ways in which evolutionary conserved processes operate in humans will only come from the investigation of human themselves, studies in Drosophila will result in a better undesrtanding of the gene networks involved, and how their perturbations in humans can lead to disease.Le malattie da prioni, dette anche encefalopatie spongiformi trasmissibili (TSE), comprendono un gruppo di malattie neurodegenerative che colpiscono l’uomo e altre specie di mammiferi. Tutte queste patologie hanno la caratteristica comune di presentare lunghi periodi di incubazione seguiti da una patologia cronica a carico del sistema nervoso che ha sempre esito fatale.
A tutt’oggi, la teoria più accreditata per spiegare le TSE è la “Protein Only Hypothesis” [1], secondo la quale l’agente responsabile di queste malattie è una proteina in grado di replicarsi autonomamente, il prione (PrPSc). Il prione rappresenterebbe un’isoforma patologica di una proteina normalmente presente nelle cellule, la proteina prionica (PrPC), e che risulta particolarmente concentrata a livello delle cellule nervose.
Nell’uomo, le malattie da prioni sono presenti in tre forme: i) infettiva, dovuta al meccanismo di conversione della proteina prionica nella sua isoforma patologica mediata dalla presenza di PrPSc, come nel caso del kuru e della variante della malattia di Creuzfeldt-Jacobs (vCJD); ii) sporadica, in seguito al cambiamento spontaneo della forma normale in PrPSc con un meccanismo non ancora noto, come, ad esempio nel caso della CJD, e infine una forma iii) ereditaria, trasmessa come carattere autosomico dominante associato a mutazioni a carico del gene PRNP codificante la proteina prionica. E’ questo il caso di malattie quali l’insonnia familiare fatale (IFF), la malattia di Gerstmann-Straussler-Scheinker (GSS) e la forma familiare della CJD (fCJD).
La straordinaria conservazione strutturale e funzionale dei geni in organismi diversi ha permesso di utilizzare modelli animali, dal lievito ai primati, per accrescere la nostra conoscenza della biologia dell’uomo.
Per poter contribuire al chiarimento della biologia dei prioni, del meccanismo patogenetico e del ruolo svolto dalle diverse mutazioni, abbiamo analizzato la possibilità di impiegare come organismo modello Drosophila melanogaster, già ampiamente utilizzata con successo per lo studio di altre malattie neurodegenerative umane. Gli invertebrati, a differenza dei mammiferi, risultano particolarmente utili nello studio di geni la cui funzione è sconosciuta in quanto permettono di applicare l’analisi genetica in modo sistematico. La scelta del modello Drosophila si basa sul fatto che questo organismo presenta, tra gli invertebrati, la massima omologia con il genoma umano, un sistema nervoso particolarmente evoluto e un tempo di generazione breve. Inoltre, data l’ampia varietà di tecniche molecolari applicabili, permette un’analisi sistematica offrendo la possiblità di chiarire la funzione di geni in modo relativamente rapido ed efficiente rispetto ad altri modelli animali.
Ci siamo quindi proposti da un lato di creare un modello animale per lo studio della funzione della PrP umana normale e mutata che permetta di approfondire i processi neurodegenerativi alla base delle TSE, e dall’altro di utilizzare il moscerino della frutta per effettuare un rapido screening genetico di alcune tra le mutazioni note, in modo da poter determinare quelle che svolgono un ruolo importante nella patogenesi di queste malattie. Tra tutte le mutazioni finora identificate ne sono state scelte tre perchè rappresentative delle tre forme di TSE ereditarie nell’uomo: P102L, associata alla GSS, D178N/129M, associata alla IFF, D178N/129V e E200K associate alla fCJD.
Mediante microiniezione degli embrioni di Drosophila, sono state ottenute diverse linee di moscerini transgenici per costrutti codificanti la proteina prionica umana (H-PrP) wild type oppure recante le mutazioni indicate. Avvalendosi del sistema di espressione binario UAS/GAL4, sono stati allestiti gli incroci per promuovere l’espressione tessuto-specifica dei diversi transgeni, in particolare a livello ubiquitario, dell’intero sistema nervoso e nei motoneuroni.
E’ stato così possibile osservare che l’espressione delle diverse forme di H-PrP non interferisce con le fasi dello sviluppo del moscerino mentre nell’adulto causa un’alterazione del fenotipo comportamentale che si aggrava progressivamente in relazione all’età degli individui. Con il trascorrere dei giorni, i moscerini esprimenti H-PrP manifestano una progressiva perdita del controllo dei movimenti delle zampe, tremori e perdita dell’equilibrio, ai quali si accompagna una sempre più evidente lentezza dei movimenti, fino alla pressoché totale immobilità e alla morte precoce. I fenotipi motori sono stati analizzati utilizzando specifici test comportamentali. Inoltre, per valutare se i fenotipi patologici osservati fossero imputabili, a livello cerebrale, alla comparsa di vacuolizzazione/spongiosi e/o all’accumulo di PrPSc, sono state osservate le sezioni istologiche ottenute dall’inclusione delle sole teste di moscerini, collezionate a tempi di invecchiamento diversi, in modo da monitorare l’eventuale comparsa di fenomeni degenerativi in dipendenza dell’età degli individui.
Nel loro complesso, i risultati ottenuti sembrano indicare che Drosophila melanogaster possa rappresentare un valido modello animale da utilizzare nello studio delle malattie da prioni ereditarie. In particolare, la progressione temporale dei sintomi e il tipo di sintomatologia osservata sembrano riprodurre l’evoluzione delle TSE nei mammiferi, supportando così la validità del modello animale qui proposto.
Mentre le conoscenze dei processi che operano nell’uomo potranno essere chiariti solamente studiando l’uomo stesso, gli studi condotti su Drosophila permettono di approfondire quali mutazioni sono coinvolte e come la loro espressione possa portare allo sviluppo della malattia
Can offshoring increase quality? A dynamic model
Full text linkWe propose a dynamic model to study the problem of relocating pro- duction to a foreign country, where production costs are lower. The idea is to investigate the impact of offshoring on the quality of the manufac- tured goods in a simple dynamic model, which is analytically treatable. What we will show is that, under the assumptions of our model, if the trading costs are sufficiently convenient, the quality increases with off- shoring
Polarization and coherence in mean field games driven by private and social utility
Full text linkWe study a mean field game in continuous time over a finite horizon, T, where
the state of each agent is binary and where players base their strategic
decisions on two, possibly competing, factors: the willingness to align with
the majority (conformism) and the aspiration of sticking with the own type
(stubbornness). We also consider a quadratic cost related to the rate at which
a change in the state happens: changing opinion may be a costly operation.
Depending on the parameters of the model, the game may have more than one Nash equilibrium, even though the corresponding N-player game does not. Moreover, it exhibits a very rich phase diagram, where polarized/unpolarized,
coherent/incoherent equilibria may coexist, except for T small, where the
equilibrium is always unique. We fully describe such phase diagram in closed
form and provide a detailed numerical analysis of the N-player counterpart of
the mean field game. In this finite dimensional setting, the equilibrium
selected by the population of players is always coherent (favoring the
subpopulation whose type is aligned with the initial condition), but it does
not necessarily minimize the cost functional. Rather, it seems that, among the
coherent ones, the equilibrium prevailing is the one that most benefits the
underdog subpopulation forced to change opinion
Are transaction taxes a cause of financial instability?
No full textWe analyze a stylized market where NN boundedly rational agents may decide to trade or not a share of a risky asset at subsequent trading dates. Agents’ payoff depends on returns, which are endogenously determined taking into account observed and forecasted demand and an exogenous transaction tax. We study the time evolutions of demand, returns and market activity. We show that the introduction of a transaction tax generally helps in reducing variability of returns and market activity. On the other hand, there are market conditions under which a low taxation may lead the market into a very unstable phase characterized by the fluctuation of the fundamentals around two different regimes; indeed, under these circumstances, heteroscedasticity of time series is detected and statistically analyzed
OPTIMAL POLICIES IN TWO-STEP BINARY GAMES UNDER SOCIAL PRESSURE AND LIMITED RESOURCES
No full textIn this paper, we propose a model where binary games with many players are implemented at two subsequent dates. An external authority sets incentives to maximize the gain deriving from the project. We show that the interplay between the optimal participation shares at the two subsequent dates makes the optimal strategy nontrivial and, to some extent, unexpected. As an application, in the context of an insurgence muting into an armed rebellion, we study the emergence of escalation effects when many actors interact taking into account social recognition
Mean-Field Modeling of Green Technology Adoption: A Competition for Incentives
No full textThis paper investigates the role of fiscal incentives in promoting the transition to a green economy using a dynamic mean-field game framework. By modeling firms as representative agents undergoing an environmentally sustainable transition, we analyze two distinct types of incentive structure: fixed incentives and incentives based on the average behavior of firms. The findings underscore the importance of balancing incentive structures to avoid economic inefficiencies and ensure a smooth ecological transition
Electron Spin Polarization Transfer and Radical - Triplet Pair Polarization in Nitroxide - C60 Derivative Systems
No full textNitroxide free radical/[60]fullerene derivative liquid solutions photoexcited by visible laser pulses are investigated by time-resolved EPR. Both radical and triplet excited fullerene spin-polarized EPR signals are observed. Their time evolution is examined in terms of CIDEP effects due to electron spin polarization transfer from the initially polarized triplet to the nitroxide and to spin polarization generated by the radical triplet pair mechanism. Radical and triplet spin relaxation times and rate constants for the processes of polarization transfer and radical triplet pair mechanism are obtained
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