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Now showing items 16421-16440 of 24408
  • R. 
    Haapasalo, Eero ((193)
  • Laaka, Maija-Leena (1966)
  • Lehtinen, Esa (2002)
  • Hattula, Katarina (Helsingin yliopisto, 2007)
    Rab8 and its interacting proteins as regulators of cell polarization During the development of a multi-cellular organism, progenitor cells have to divide and migrate appropriately as well as organize their differentiation with one another, in order to produce a viable embryo. To divide, differentiate and migrate cells have to undergo polarization, a process where internal and external components such as actin, microtubules and adhesion receptors are reorganized to produce a cell that is asymmetric, with functionally different surfaces. Also in the adult organism there is a continuous need for these processes, as cells need to migrate in response to tissue damage and to fight infection. Improper regulation of cell proliferation and migration can conversely lead to disease such as cancer. GTP-binding proteins function as molecular switches by cycling between a GTP-bound (active) conformation and a GDP-bound (inactive) conformation. The Ras super-family of small GTPases are found in all eukaryotic cells. They can be functionally divided into five subfamilies. The Ras family members mainly regulate gene expression, controlling cell proliferation and differentiation. Ras was in fact the first human oncogene to be characterized, and as much as 30% of all human tumors may be directly or indirectly caused by mutations of Ras molecules The Rho family members mainly regulate cytoskeletal reorganization. Arf proteins are known to regulate vesicle budding and Rab proteins regulate vesicular transport. Ran regulates nuclear transport as well as microtubule organization during mitosis. The focus of the thesis of Katarina Hattula, is on Rab8, a small GTPase of the Rab family. Activated Rab8 has previously been shown to induce the formation of new surface extensions, reorganizing both actin and microtubules, and to have a role in directed membrane transport to cell surfaces. However, the exact membrane route it regulates has remained elusive. In the thesis three novel interactors of Rab8 are presented. Rabin8 is a Rab8-specific GEF that localizes to vesicles where it presumably recruits and activates its target Rab8. Its expression in cells leads to remodelling of actin and the formation of polarized cell surface domains. Optineurin, known to be associated with a leading cause of blindness in humans (open-angle glaucoma), is shown to interact specifically with GTP-bound Rab8. Rab8 binds to an amino-terminal region and interestingly, the Huntingtin protein binds a carboxy-terminal region of optineurin. (Aberrant Huntingtin protein is known to be the cause Huntington s disease in humans.) Co-expression of Huntingtin and optineurin enhanced the recruitment of Huntingtin to Rab8-positive vesicular structures. Furthermore, optineurin promoted cell polarization in a similar way to Rab8. A third novel interactor of Rab8 presented in this thesis is JFC1, a member of the synaptogamin-like protein (Slp) family. JFC1 interacts with Rab8 specifically in its GTP-bound form, co-localizes with endogenous Rab8 on tubular and vesicular structures, and is probably involved in controlling Rab8 membrane dynamics. Rab8 is in this thesis work clearly shown to have a strong effect on cell shape. Blocking Rab8 activity by expression of Rab8 RNAi, or by expressing the dominant negative Rab8 (T22N) mutant leads to loss of cell polarity. Conversely, cells expressing the constitutively active Rab8 (Q67L) mutant exhibit a strongly polarized phenotype. Experiments in live cells show that Rab8 is associated with macropinosomes generated at ruffling areas of the membrane. These macropinosomes fuse with or transform into tubules that move toward the cell centre, from where they are recycled back to the leading edge to participate in protrusion formation. The biogenesis of these tubules is shown to be dependent on both actin and microtubule dynamics. The Rab8-specific membrane route studied contained several markers known to be internalized and recycled (1 integrin, transferrin, transferrin receptor, cholera toxin B subunit (CTxB), and major histocompatibility complex class I protein (MHCI)). Co-expression studies revealed that Rab8 localization overlaps with that of Rab11 and Arf6. Rab8 is furthermore clearly functionally linked to Arf6. The data presented in this thesis strongly suggests a role for Rab8 as a regulator for a recycling compartment, which is involved in providing structural and regulatory components to the leading edge to participate in protrusion formation.
  • Furuhjelm, Johanna (Helsingin yliopisto, 2004)
  • Hakola, Tuulia (1999)
    The pension system forms a highly significant part of the whole social welfare system. The impact of the pension system is not limited to the financial aspects, but, for example, labour markets, savings, capital accumulation and income distribution can be affected. This study considers the effects of the pension system on the labour supply of the elderly. As the Finnish pension system is mainly a Pay-As-You-Go system, the concurrent change in the demographic structure, compounded by increased early retirements, is likely to yield strong pressures on the financing of the current pension system. The study evaluates early withdrawals by the elderly from the labour force. It assesses the significance of the implicit economic incentives, provided by the pension system, to retire early. The incentives are measured by an option value to retirement. Transition probabilities are considered in a random effects probit model, using the data from the Employment Registry of the Statistics Finland. The empirical results provide evidence that economic incentives matter also to the Finnish labour force. The results reveal that if an individual gains financially by postponing his retirement, he is more likely to do so. Simulations show that two of the implemented and contemplated policy reforms have a desired impact on the retirement probabilities.
  • Hakola, Tuulia (1999)
    Eläkejärjestelmä on olennainen osa suomalaista sosiaaliturvaa. Eläkejärjestelmän vaikutukset eivät rajoitu ainoastaan sen suoriin taloudellisiin vaikutuksiin, vaan eläkejärjestelmäl1ä voi olla vaikutusta esimerkiksi työmarkkinoihin, säästämiseen, pääoman määrään ja tulonjakoon. Tässä tutkimuksessa kesktytään ikääntyneiden työmarkkinavaikutuksiin. Varhaiseläkkeelle siirtyminen on myös Suomessa ollut kasvussa. Tämä voi lisätä jakojärjestelmään perustuvan eläkejärestelmän rahoitusvaikutuksia - varsinkin kun samaan aikaan Suomessa tapahtuu voimakas ikärakenteen muutos. Tutkimuksessa tarkastellaan erityisesti taloudellisia kannustimia. Kannustimien mittarina kaytetään optioarvoa - eläkkeelle jäämisen vaihtoehtoiskustannusta. Eläkkeellesiirtymistodennäköisyyksiä arvioidaan satunnaisvaikutteisessa probit-mallissa. Aineistona käytetään Tilastokeskuksen Työssäkäyntitilastoa. Tutkimus tukee väitettä, jonka mukaan taloudellisilla kannustimilla on merkitystä myös Suomessa. Tulosten mukaan eläkkeelle siirtyminen on sita epätodennäköisempää, mitä enemmän eläkepäätöksen lykkäämisestä on taloudellista hyötyä. Työssä simuloidaan myös kaksi politiikkamuutosta. Kumpikin simulaatio vahvistaa toteutettujen toimenpiteiden vaikutuksen olevan halutun suuntaista.
  • Piirainen, Armida (1933)
  • Niemi, Aki (2003)
    Tutkimus kasittelee metsanuudistusalan inventointiin sovellettavia tilastollisia menetelmia ja naiden teoriaa. Tavoitteena on taimikon tilajarjestysta kuvaavien spatiaalisten pisteprosessimallien konstruointi seka mallipohjaisen otantateorian kehittaminen otantaan stationaarisesta pisteprosessista. Metsanuudistamisessa kaytetyt maanmuokkaus- ja uudistusmenetelmat vaikuttavat voimakkaasti nuoren taimikon tilajarjestykseen. Maanmuokkauksen vaikutus on vallitseva. Istutetut ja kylvetyt taimet sijaitsevat muokkausjaljissa, mutta myos luontaisesti uudistuneiden taimien tiheys on suurempi muokkausjalkien sisalla kuin naiden ulkopuolella. Tutkimus esittelee uuden pisteprosessimallin: RACS-generoiman Cox-prosessin (RACS = random closed set). Mallin rakennetekijana on maanmuokkausjalkia kuvaava satunnainen suljettu joukko, jonka jakamana taimitiheys joukon sisalla (muokkausjaljissa) on suurempi kuin ulkopuolella. Klassinen spatiaalisen otannan teoria kasittelee otantaa stationaarisesta jatkuvaparametrisesta satunnaiskentasta, kun estimoitavana on satunnaiskentan realisaation keskiarvo. Teorian keskeinen tyokalu on satunnaiskentan kovarianssifunktio, jonka tulee olla monotonisesti vaheneva ja positiivisesti definiitti. Metsanuudistusalan koealaotannassa keskimaarainen taimitiheys estimoidaan sijoittamalla taimikkoon koealoja, ja laskemalla nailta taimien lukumaara. Klassinen otantateoria ei kuitenkaan ole suoraan sovellettavissa kyseiseen tilanteeseen. Ongelma ratkaistaan muunnoksella stationaarisen pisteprosessin havainnoinnista stationaariseen jatkuvaparametriseen satunnaiskenttaan. Tutkimuksessa johdetaan kyseisen satunnaiskentan kovarianssifunktio. Tama esitetaan pisteprosessin intensiteetin ja parikorrelaatiofunktion seka otantakoealan pinta-alan avulla. Tyon empiirisessa osassa konstruoidaan RACS-generoima Cox-prosessimalli seka muokatulle etta laikutetulle uudistusalalle. Mallien perustana on maanmuokkauksen kaytannon suoritusta koskevat ohjeistukset. Vertailussa vastaaviin havaintoaineistoihin mallit kuvaavat kohtuullisen hyvin todellisten taimikoiden tilajarjestysta. Lahteet: Matern, B. (1960). Spatial variation. Meddelanden fran Statens Skogsforskningsinstitut 49(5). Stoyan, D. & Kendall, W. S. & Mecke, J. (1995). Stochastic Geometry and Its Applications, 2. painos. Wiley, Chichester.