Lamellarin D bioconjugates I: synthesis and cellular internalization of PEG-derivatives

Herein is reported the design and synthesis of poly(ethylene glycol) derivatives of Lamellarin D with the aim of modulating their physicochemical properties, and improving the biological activity. Mono-, di- and tri-PEG conjugates with improved solubility were obtained in 18-57% overall yields from the corresponding partially protected phenolic derivatives of Lamellarin D. Conjugates 1-9 were tested in a panel of three human tumor cell lines (MDA-MB-231 breast, A-549 lung and HT-29 colon) to evaluate their cytotoxicity. Several compounds exhibited enhanced cellular internalization, and more than 85% of the derivatives showed a lower GI50 than Lam-D. Furthermore, cell cycle arrest at G2 phase, and apoptotic cell-death pathways were determined for Lamellarin D and these derivatives.

Mobile Subscription Acquisition and Retention Costs - An Actvity-Based Model

The objective of this master’s thesis was to develop a model for mobile subscription acquisition cost, SAC, and mobile subscription retention cost, SRC, by applying activity-based cost accounting principles. The thesis was conducted as a case study for a telecommunication company operating on the Finnish telecommunication market. In addition to activity-based cost accounting there were other theories studied and applied in order to establish a theory framework for this thesis. The concepts of acquisition and retention were explored in a broader context with the concepts of customer satisfaction, loyalty and profitability and eventually customer relationship management to understand the background and meaning of the theme of this thesis. The utilization of SAC and SRC information is discussed through the theories of decision making and activity-based management. Also, the present state and future needs of SAC and SRC information usage at the case company as well as the functions of the company were examined by interviewing some members of the company personnel. With the help of these theories and methods it was aimed at finding out both the theory-based and practical factors which affect the structure of the model. During the thesis study it was confirmed that the existing SAC and SRC model of the case company should be used as the basis in developing the activity-based model. As a result the indirect costs of the old model were transformed into activities and the direct costs were continued to be allocated directly to acquisition of new subscriptions and retention of old subscriptions. The refined model will enable managing the subscription acquisition, retention and the related costs better through the activity information. During the interviews it was found out that the SAC and SRC information is also used in performance measurement and operational and strategic planning. SAC and SRC are not fully absorbed costs and it was concluded that the model serves best as a source of indicative cost information. This thesis does not include calculating costs. Instead, the refined model together with both the theory-based and interview findings concerning the utilization of the information produced by the model will serve as a framework for the possible future development aiming at completing the model.

Conservation Laws in Cellular Automata

Conservation laws in physics are numerical invariants of the dynamics of a system. In cellular automata (CA), a similar concept has already been defined and studied. To each local pattern of cell states a real value is associated, interpreted as the “energy” (or “mass”, or . . . ) of that pattern.The overall “energy” of a configuration is simply the sum of the energy of the local patterns appearing on different positions in the configuration. We have a conservation law for that energy, if the total energy of each configuration remains constant during the evolution of the CA. For a given conservation law, it is desirable to find microscopic explanations for the dynamics of the conserved energy in terms of flows of energy from one region toward another. Often, it happens that the energy values are from non-negative integers, and are interpreted as the number of “particles” distributed on a configuration. In such cases, it is conjectured that one can always provide a microscopic explanation for the conservation laws by prescribing rules for the local movement of the particles. The onedimensional case has already been solved by Fuk´s and Pivato. We extend this to two-dimensional cellular automata with radius-0,5 neighborhood on the square lattice. We then consider conservation laws in which the energy values are chosen from a commutative group or semigroup. In this case, the class of all conservation laws for a CA form a partially ordered hierarchy. We study the structure of this hierarchy and prove some basic facts about it. Although the local properties of this hierarchy (at least in the group-valued case) are tractable, its global properties turn out to be algorithmically inaccessible. In particular, we prove that it is undecidable whether this hierarchy is trivial (i.e., if the CA has any non-trivial conservation law at all) or unbounded. We point out some interconnections between the structure of this hierarchy and the dynamical properties of the CA. We show that positively expansive CA do not have non-trivial conservation laws. We also investigate a curious relationship between conservation laws and invariant Gibbs measures in reversible and surjective CA. Gibbs measures are known to coincide with the equilibrium states of a lattice system defined in terms of a Hamiltonian. For reversible cellular automata, each conserved quantity may play the role of a Hamiltonian, and provides a Gibbs measure (or a set of Gibbs measures, in case of phase multiplicity) that is invariant. Conversely, every invariant Gibbs measure provides a conservation law for the CA. For surjective CA, the former statement also follows (in a slightly different form) from the variational characterization of the Gibbs measures. For one-dimensional surjective CA, we show that each invariant Gibbs measure provides a conservation law. We also prove that surjective CA almost surely preserve the average information content per cell with respect to any probability measure.

Neuropeptide Y at the cellular level – Studies on PreproNPY L7P Polymorphism and the Mitochondrial Form of NPY

Neuropeptide Y (NPY) is a widely expressed neurotransmitter in the central and peripheral nervous systems. Thymidine 1128 to cytocine substitution in the signal sequence of the preproNPY results in a single amino acid change where leucine is changed to proline. This L7P change leads to a conformational change of the signal sequence which can have an effect on the intracellular processing of NPY. The L7P polymorphism was originally associated with higher total and LDL cholesterol levels in obese subjects. It has also been associated with several other physiological and pathophysiological responses such as atherosclerosis and T2 diabetes. However, the changes on the cellular level due to the preproNPY signal sequence L7P polymorphism were not known. The aims of the current thesis were to study the effects of the [p.L7]+[p.L7] and the [p.L7]+[p.P7] genotypes in primary cultured and genotyped human umbilical vein endothelial cells (HUVEC), in neuroblastoma (SK-N-BE(2)) cells and in fibroblast (CHO-K1) cells. Also, the putative effects of the L7P polymorphism on proliferation, apoptosis and LDL and nitric oxide metabolism were investigated. In the course of the studies a fragment of NPY targeted to mitochondria was found. With the putative mitochondrial NPY fragment the aim was to study the translational preferences and the mobility of the protein. The intracellular distribution of NPY between the [p.L7]+[p.L7] and the [p.L7]+[p.P7] genotypes was found to be different. NPY immunoreactivity was prominent in the [p.L7]+[p.P7] cells while the proNPY immunoreactivity was prominent in the [p.L7]+[p.L7] genotype cells. In the proliferation experiments there was a difference in the [p.L7]+[p.L7] genotype cells between early and late passage (aged) cells; the proliferation was raised in the aged cells. NPY increased the growth of the cells with the [p.L7]+[p.P7] genotype. Apoptosis did not seem to differ between the genotypes, but in the aged cells with the [p.L7]+[p.L7] genotype, LDL uptake was found to be elevated. Furthermore, the genotype seemed to have a strong effect on the nitric oxide metabolism. The results indicated that the mobility of NPY protein inside the cells was increased within the P7 containing constructs. The existence of the mitochondria targeted NPY fragment was verified, and translational preferences were proved to be due to the origin of the cells. Cell of neuronal origin preferred the translation of mature NPY (NPY1-36) when compared to the non neuronal cells that translated both, NPY and the mitochondrial fragment of NPY. The mobility of the mitochondrial fragment was found to be minimal. The functionality of the mitochondrial NPY fragment remains to be investigated. L7P polymorphism in the preproNPY causes a series of intracellular changes. These changes may contribute to the state of cellular senescence, vascular tone and lead to endothelial dysfunction and even to increased susceptibility to diseases, like atherosclerosis and T2 diabetes.

Granulation tissue formation -The effect of hydroxyapatite coating of cellulose on cellular differentiation

Haavan jyväiskudoksen muodostuminen – Hydroksiapatiittipinnoi-tetun selluloosasienen vaikutus solujen erilaistumiseen paranemisprosessin aikana Etsittäessä uusia luun bioyhteensopivia täytemateriaaleja selluloosasieni päällystettiin luun koostumusta muistuttavalla runsaasti piitä sisältävällä hydroksiapatiittikerroksella. Vastoin odotuksia hydroksiapatiittipinnoitettu selluloosa ei parantanut luun kasvua, vaan päinvastoin ylläpiti tulehdusta ja sidekudossolujen hakeutumista vamma-alueelle. Ihon alle implantoituna sama sienimateriaali edisti merkittävästi haavan verekkään jyväiskudoksen kasvua. Tämän löydöksen perusteella hydroksiapatiittipinnoitetun selluloosasienen vaikutusta haavan soluihin paranemisprosessin aikana tutkittiin tarkemmin ja havaittiin, että tulehdussolujen lisäksi sieniin kertyi tavallista enemmän sekä hematopoieettisia että mesenkymaalisia kantasoluja. Hematopoieettiset kantasolut sijaitsevat luuytimessä lähellä luun sisäpintaa. Luun hydroksiapatiitista vapautuu kalsiumioneja luun jatkuvan fysiologisen uudismuodostuksen ja hajottamisen yhteydessä. Kantasolut etsiytyvät luuytimeen kalsiumia aistivien reseptorien välityksellä. Koska luun pintakerrosta muistuttavasta hydroksiapatiittipinnoitteesta vapautuu kalsiumia, tämän ajateltiin toimivan selityksenä sille, että hematopoieettiset kantasolut hakeutuvat runsaslukuisesti juuri hydroksiapatiittipinnoitettuihin selluloosasieniin. Tämän hypoteesin mukaisesti hydroksiapatiittipinnoitettujen selluloosapalkkien läheisyydestä löydettiin suuria määriä kalsiumreseptoreja sisältäviä soluja. Jatkotutkimuksissa todettiin lisäksi, että hematopoieettiset kantasolut pystyivät sienissä erilaistumaan hemoglobiinia tuottaviksi soluiksi. Havaittujen punasolulinjan merkkiaineiden perusteella näyttäisikin siltä, että haavan paranemiskudoksessa tapahtuu paranemisen aikana ekstramedullaarista erytropoieesia. Nämä soluja ohjaavat vaikutukset saattavat olla hyödyllisiä vaikeasti paranevien haavojen hoidossa.

On Undecidable Dynamical Properties of Reversible One-Dimensional Cellular Automata

Cellular automata are models for massively parallel computation. A cellular automaton consists of cells which are arranged in some kind of regular lattice and a local update rule which updates the state of each cell according to the states of the cell's neighbors on each step of the computation. This work focuses on reversible one-dimensional cellular automata in which the cells are arranged in a two-way in_nite line and the computation is reversible, that is, the previous states of the cells can be derived from the current ones. In this work it is shown that several properties of reversible one-dimensional cellular automata are algorithmically undecidable, that is, there exists no algorithm that would tell whether a given cellular automaton has the property or not. It is shown that the tiling problem of Wang tiles remains undecidable even in some very restricted special cases. It follows that it is undecidable whether some given states will always appear in computations by the given cellular automaton. It also follows that a weaker form of expansivity, which is a concept of dynamical systems, is an undecidable property for reversible one-dimensional cellular automata. It is shown that several properties of dynamical systems are undecidable for reversible one-dimensional cellular automata. It shown that sensitivity to initial conditions and topological mixing are undecidable properties. Furthermore, non-sensitive and mixing cellular automata are recursively inseparable. It follows that also chaotic behavior is an undecidable property for reversible one-dimensional cellular automata.

Viral and cellular modulation of virus-induced apoptosis in experimental infection models

The aim of this study was to investigate herpes simplex virus type 1 (HSV-1)- and measles virus (MV)-induced cell death. HSV-1 with deletion in genes encoding infected cell protein (ICP)4 and protein kinase Us3 (d120) induced apoptosis and cathepsin activation in epithelial (HEp-2) and monocytic (U937) cells. Inhibition of cathepsin activity decreased the amount of d120-induced apoptosis indicating that d120-induced apoptosis could be cathepsin-mediated. Also, HSV-1 infection increased caspase activation suggesting that d120-induced apoptosis is probably caspase-mediated. Cystatin treatment decreased the activity of cathepsins and the replication of HSV-1 indicating that cathepsins contribute to HSV-1 infection. Interestingly, d120 induced also necroptosis in monocytic cells. This is the first report on necroptosis in HSV-1- infected cells. MV induced apoptosis in uninfected bystander T lymphocytes, probably via interaction of MV-infected monocytes with uninfected lymphocytes. The expression of death receptor Fas was clearly increased on the surface of lymphocytes. The number of apoptotic cells and the activation of cathepsins and caspases were increased in MVinfected U937 cells suggesting that MV-induced apoptosis could be cathepsin- and caspase-mediated. Cystatin treatment inhibited cathepsin activities but not MV-induced apoptosis. Besides HSV-1-induced apoptosis, innate immune responses were studied in HSV-1-infection. HSV-1 viruses with either ICP4 and Us3, or Us3 deletion only, increased the expression of Toll-like receptor (TLR)3 and stimulated its downstream pathways leading to increased expression of type I interferon gene and to functional interferons. These findings suggest that besides controlling apoptosis, HSV-1 ICP4 and Us3 genes are involved in the control of TLR3 response in infected cell.

The Cellular Oxygen Sensor PHD2 in Cancer Growth

Adequate supply of oxygen is essential for the survival of multicellular organisms. However, in several conditions the supply of oxygen can be disturbed and the tissue oxygenation is compromised. This condition is termed hypoxia. Oxygen homeostasis is maintained by the regulation of both the use and delivery of oxygen through complex, sensitive and cell-type specific transcriptional responses to hypoxia. This is mainly achieved by one master regulator, a transcription factor called hypoxiainducible factor 1 (HIF-1). The amount of HIF-1 is under tight oxygen-dependent control by a family of oxygen-dependent prolyl hydroxylase domain proteins (PHDs) that function as the cellular oxygen sensors. Three family members (PHD1-3) are known to regulate HIF of which the PHD2 isoform is thought to be the main regulator of HIF-1. The supply of oxygen can be disturbed in pathophysiological conditions, such as ischemic disorders and cancer. Cancer cells in the hypoxic parts of the tumors exploit the ability of HIF-1 to turn on the mechanisms for their survival, resistance to treatment, and escape from the oxygen- and nutrient-deprived environment. In this study, the expression and regulation of PHD2 were studied in normal and cancerous tissues, and its significance in tumor growth. The results show that the expression of PHD2 is induced in hypoxic cells. It is overexpressed in head and neck squamous cell carcinomas and colon adenocarcinomas. Although PHD2 normally resides in the cytoplasm, nuclear translocation of PHD2 was also seen in a subset of tumor cells. Together with the overexpression, the nuclear localization correlated with the aggressiveness of the tumors. The nuclear localization of PHD2 caused an increase in the anchorage-independent growth of cancer cells. This study provides information on the role of PHD2, the main regulator of HIF expression, in cancer progression. This knowledge may prove to be valuable in targeting the HIF pathway in cancer treatment.

Cellular immune response of Curraleiro Pé-duro and Nellore calves following Mycobacterium bovis-BCG vaccination

The present study aimed to assess the CD4, CD8 and γδ blood levels for Curraleiro Pé-duro, as well as the specific IFN-γ response after BCG vaccination using flow cytometry. The specific immune response against BCG was also evaluated by tuberculin skin test, performed before and 45 days after the vaccination. For comparison purposes, the same parameters were investigated on Nellore calves, an exotic bovine with resistance previously demonstrated. Naturally, Curraleiro Pé-duro animals had greater levels of CD4, CD8 and γδ lymphocytes (p<0.05). In response to vaccine, Curraleiro Pé-duro showed greater ability to respond specifically to BCG, generating resistance profile (Th1), evidenced by greater number of antigen specific CD4+ cells producing IFN-γ (p<0.05) and also higher tuberculin skin test reaction (p<0.05). Additionally, vaccinated Curraleiro Pé-duro calves had higher CD4 cells numbers than both Nellore control (p<0.05) and vaccinated groups (p<0.05). Curraleiro Pé-duro calves' higher basal lymphocytes blood level and stronger response in both IFN-γ and tuberculin skin test parameters probably play a positive role on protection/resistance to Mycobacterium bovis.

Cellular responses to stress and kinase signaling activation : apoptosis and differentiation

Stressignaler avkänns många gånger av membranbundna proteiner som översätter signalerna till kemisk modifiering av molekyler, ofta proteinkinaser Dessa kinaser överför de avkodade budskapen till specifika transkriptionsfaktorer genom en kaskad av sekventiella fosforyleringshändelser, transkriptionsfaktorerna aktiverar i sin tur de gener som behövs för att reagera på stressen. En av de mest kända måltavlorna för stressignaler är transkriptionsfaktor AP-1 familjemedlemen c-Jun. I denna studie har jag identifierat den nukleolära proteinet AATF som en ny regulator av c-Jun-medierad transkriptionsaktivitet. Jag visar att stresstimuli inducerar omlokalisering av AATF vilket i sin tur leder till aktivering av c-Jun. Den AATF-medierad ökningen av c-Jun-aktiviteten leder till en betydande ökning av programmerad celldöd. Parallellt har jag vidarekarakteriserat Cdk5/p35 signaleringskomplexet som tidigare har identifierats i vårt laboratorium som en viktig faktor för myoblastdifferentiering. Jag identifierade den atypiska PKCξ som en uppströms regulator av Cdk5/p35-komplexet och visar att klyvning och aktivering av Cdk5 regulatorn p35 är av fysiologisk betydelse för differentieringsprocessen och beroende av PKCξ aktivitet. Jag visar att vid induktion av differentiering fosforylerar PKCξ p35 vilket leder till calpain-medierad klyvning av p35 och därmed ökning av Cdk5-aktiviteten. Denna avhandling ökar förståelsen för de regulatoriska mekanismer som styr c-Jun-transkriptionsaktiviteten och c-Jun beroende apoptos genom att identifiera AATF som en viktig faktor. Dessutom ger detta arbete nya insikter om funktionen av Cdk5/p35-komplexet under myoblastdifferentiering och identifierar PKCξ som en uppströms regulator av Cdk5 aktivitet och myoblast differentiering.

Bronchoalveolar lavage as a tool for evaluation of cellular alteration during Aelurostrongylus abstrusus infection in cats

Bronchoalveolar lavage (BAL) is a procedure that retrieves cells and other elements from the lungs for evaluation, which helps in the diagnosis of pulmonary diseases. The aim of this study was to perform this procedure for cellular analysis of BAL fluid alterations during experimental infection with Aelurostrongylus abstrusus in cats. Fourteen cats were individually inoculated with 800 third stage larvae of A. abstrusus and five non-infected cats lined as a control group. The BAL procedure was performed through the use of an endotracheal tube on the nineteen cats with a mean age of 18 months, on 0, 30, 60, 90, 120, 180 and 270 days after infection. Absolute cell counts in the infected cats revealed that alveolar macrophages and eosinophils were the predominant cells following infection. This study shows that the technique allows us to retrieve cells and first stage larvae what provides information about the inflammatory process caused by aelurostrongylosis.

Isolation, expansion and differentiation of cellular progenitors obtained from dental pulp of agouti (Dasyprocta prymnolopha Wagler, 1831)

Abstract: The study aimed to isolate, expand, differentiate and characterize progenitor cells existent in the dental pulp of agouti. The material was washed with PBS solution and dissociated mechanically with the aid of a scalpel blade on plates containing culture medium D-MEM/F-12, and incubated at 5% CO2-37⁰C. The growth curve, CFU assay, osteogenic/adipogenic differentiation and characterization were obtained from the isolation. The cells began to be released from the explant tissue around the 7th day of culture. By day 22 of culture, cells reached 80% confluence. At the UFC test, 81 colonies were counted with 12 days of cultivation. The growth curves before and after freezing showed a regular growth with intense proliferation and clonogenic potential. The cell differentiation showed formation of osteoblasts and fat in culture, starting at 15 days of culture in a specific medium. Flow cytometry (FACs) was as follows: CD34 (positive), CD14 (negative), CD45 (negative), CD73 (positive), CD79 (negative), CD90 (positive), CD105 (positive), demonstrating high specificity and commitment of isolated cells with mesenchymal stem cells strains. These results suggest the existence of a cell population of stem cells with mesenchymal features from the isolated tissue in the explants of agouti dental pulp, a potential model for study of stem cell strains obtained from the pulp tissue.

Fluorescence-based imaging of cellular defect in lysinuric protein intolerance (LPI)

Fluoresenssiperusteiset kuvantamismenetelmät lysinurisen proteiini-intoleranssin (LPI) soluhäiriön tutkimuksessa Lysinurinen proteiini-intoleranssi on suomalaiseen tautiperintöön kuuluva autosomaalisesti peit¬tyvästi periytyvä sairaus, jonka aiheuttaa kationisten aminohappojen kuljetushäiriö munuaisten ja ohutsuolen epiteelisolujen basolateraalikalvolla. Aminohappojen kuljetushäiriö johtaa moniin oirei¬siin, kuten kasvuhäiriöön, osteoporoosiin, immuunijärjestelmän häiriöihin, oksenteluun ja runsaspro¬teiinisen ravinnon nauttimisen jälkeiseen hyperammonemiaan. LPI-geeni SLC7A7 (solute carrier family 7 member 7) koodaa y+LAT1 proteiinia, joka on basolateraali¬nen kationisten ja neutraalien aminohappojen kuljettimen kevyt ketju, joka muodostaa heterodimee¬rin raskaan alayksikön 4F2hc:n kanssa. Tällä hetkellä SLC7A7-geenistä tunnetaan yli 50 LPI:n aiheut¬tavaa mutaatiota. Tässä tutkimuksessa erityyppisiä y+LAT1:n LPI-mutaatiota sekä yhdeksän C-terminaalista polypep¬tidiä lyhentävää deleetiota kuvannettiin nisäkässoluissa y+LAT1:n GFP (green fluorescent protein) -fuusioproteiineina. Tulokset vahvistivat muissa soluissa tehdyt havainnot siitä, että 4F2hc on edel¬lytyksenä y+LAT1:n solukalvokuljetukselle, G54V-pistemutantti sijaitsee solukalvolla samoin kuin vil¬lityyppinen proteiini, mutta lukukehystä muuttavia ja proteiinia lyhentäviä mutantteja ei kuljeteta solukalvoon. Lisäksi havaittiin, että poikkeuksena tästä säännöstä ovat y+LAT1-deleetioproteiinit, joista puuttui korkeintaan 50 C-terminaalista aminohappoa. Nämä lyhentyneet kuljettimet sijaitsevat solukalvolla kuten villityyppiset ja LPI-pistemutanttiproteiinit. Dimerisaation osuutta kuljetushäiriön synnyssä tutkittiin käyttämällä fluorescence resonance energy transfer (FRET) menetelmää. Heterodimeerin alayksiköistä kloonattiin ECFP (cyan) ja EYFP (yellow) fuusioproteiinit, joita ilmennettiin nisäkässoluissa, ja FRET mitattiin virtaussytometri-FRET -menetel¬mällä (FACS-FRET). Tutkimuksissa kaikkien mutanttien havaittiin dimerisoituvan yhtä tehokkaasti. Kul¬jetushäiriön syynä ei siten ole alayksiköiden dimerisaation estyminen mutaation seurauksena. Tutkimuksessa havaittiin, että kaikki mutantti-y+LAT1-transfektiot tuottavat vähemmän transfektoi¬tuneita soluja kuin villityyppisen y+LAT1:n transfektiot. Solupopulaatioissa, joihin oli tranfektoitu lu¬kukehystä muuttava tai stop-kodonin tuottava mutaatio havaittiin suurempi kuolleisuus kuin saman näytteen transfektoitumattomissa soluissa, kun taas villityyppistä tai G54V-pistemutanttia tuottavas¬sa solupopulaatiossa oli pienempi kuolleisuus kuin saman näytteen fuusioproteiinia ilmentämättö¬missä soluissa. Tulos osoittaa mutanttiproteiinien erilaiset vaikutukset niitä ilmentäviin soluihin, joko suoraan y+LAT1:n tai 4F2hc:n kautta aiheutuneina. LPIFin SLC7A7 lähetti-RNA:n määrä ei merkittävästi poikennut villityyppisen määrästä fibroblasteissa ja lymfoblasteissa. SLC7A7:n promoottorianalyysissä oli osoitettavissa säätelyalueita geenin 5’ ei-koo¬daavalla alueella sekä ensimmäisten kahden intronin alueella. LPI-taudin tautimekanismin kannalta keskeisin tekijä on kuitenkin aminohappokuljetuksen häiriö, jonka vaikutuksesta näistä aminohapoista riippuvaiset prosessit elimistössä eivät toimi normaalisti. Havaittu virheellinen y+LAT1/4F2hc kuljetuskompleksin sijainti edellyttää lisätutkimuksia sen mahdol¬lisen kliinisen merkityksen selvittämiseksi.

Subshifts with Simple Cellular Automata

A subshift is a set of in nite one- or two-way sequences over a xed nite set, de ned by a set of forbidden patterns. In this thesis, we study subshifts in the topological setting, where the natural morphisms between them are ones de ned by a (spatially uniform) local rule. Endomorphisms of subshifts are called cellular automata, and we call the set of cellular automata on a subshift its endomorphism monoid. It is known that the set of all sequences (the full shift) allows cellular automata with complex dynamical and computational properties. We are interested in subshifts that do not support such cellular automata. In particular, we study countable subshifts, minimal subshifts and subshifts with additional universal algebraic structure that cellular automata need to respect, and investigate certain criteria of `simplicity' of the endomorphism monoid, for each of them. In the case of countable subshifts, we concentrate on countable so c shifts, that is, countable subshifts de ned by a nite state automaton. We develop some general tools for studying cellular automata on such subshifts, and show that nilpotency and periodicity of cellular automata are decidable properties, and positive expansivity is impossible. Nevertheless, we also prove various undecidability results, by simulating counter machines with cellular automata. We prove that minimal subshifts generated by primitive Pisot substitutions only support virtually cyclic automorphism groups, and give an example of a Toeplitz subshift whose automorphism group is not nitely generated. In the algebraic setting, we study the centralizers of CA, and group and lattice homomorphic CA. In particular, we obtain results about centralizers of symbol permutations and bipermutive CA, and their connections with group structures.

Analysis of viral and cellular parameters which affect the fusion process of influenza viruses

In the present investigation we studied the fusogenic process developed by influenza A, B and C viruses on cell surfaces and different factors associated with virus and cell membrane structures. The biological activity of purified virus strains was evaluated in hemagglutination, sialidase and fusion assays. Hemolysis by influenza A, B and C viruses ranging from 77.4 to 97.2%, from 20.0 to 65.0%, from 0.2 to 93.7% and from 9.0 to 76.1% was observed when human, chicken, rabbit and monkey erythrocytes, respectively, were tested at pH 5.5. At this pH, low hemolysis indexes for influenza A, B and C viruses were observed if horse erythrocytes were used as target cells for the fusion process, which could be explained by an inefficient receptor binding activity of influenza on N-glycolyl sialic acids. Differences in hemagglutinin receptor binding activity due to its specificity to N-acetyl or N-glycolyl cell surface oligosaccharides, density of these cellular receptors and level of negative charges on the cell surface may possibly explain these results, showing influence on the sialidase activity and the fusogenic process. Comparative analysis showed a lack of dependence between the sialidase and fusion activities developed by influenza B viruses. Influenza A viruses at low sialidase titers (<2) also exhibited clearly low hemolysis at pH 5.5 (15.8%), while influenza B viruses with similarly low sialidase titers showed highly variable hemolysis indexes (0.2 to 78.0%). These results support the idea that different virus and cell-associated factors such as those presented above have a significant effect on the multifactorial fusion process