Browsing by Subject "regeneration"

Reptiles have long been studied in search of the mechanisms behind neuronal regeneration. This thesis delves into the regenerative areas of two emerging model species to the field of regenerative research: Pogona vitticeps (bearded dragon) and Pantherophis guttatus (corn snake). This fluorescent immunohistochemical study maps out and compares the constitutive proliferative zones in these two species to better define the focus of future comparative neurodegenerative experiments. A BrdU pulse chase experiment in conjunction with PCNA reveals proliferative zones in the lateral ventricular ependyma of both species. Stem cell niches were found in the ependymal lining adjacent to the medial cortex and dorsal ventricular ridge in both species, however, the nucleus sphericus ependyma was an active proliferative zone only in Pantherophis. Imaging of further markers in this study support the findings of the pulse chase experiment. High levels of the stem cell marker Sox2 was found in lateral ventricular ependymal cells in both species. The glial marker GFAP reveals a highly ordered array of radial glia in the cortical areas of Pogona, which is significantly reduced or absent in Pantherophis. And lastly the neuronal marker HU was found in the same cells that were BrdU positive and had migrated a short distance from the proliferative zones, which shows that the proliferative areas in the lateral ventricular lining do indeed produce neurons. The BrdU and PCNA marked cells were quantified in both species, and a brief comparison between the species showed that Pogona had a significantly higher number and concentration of proliferative cells in the proliferative zones than Pantherophis. Scattered BrdU positive cells that were neither neuronal nor positive for any other marker were also found scattered throughout the parenchyma of Pogona, and these cells remain uncharacterized. Differences between these two species are not surprising, as lizards are known to have better regenerative capabilities than snakes, however, more comparative research between these species is needed to gain further insight into the mechanisms behind their contrasting regenerative capabilities.

Aksolotlit (Ambystoma mexicanum) kykenevät regeneroimaan kokonaisia menetettyjä ruumiinosia läpi elämänsä. Viime vuosina on tehty valtavia harppauksia regeneraation mekanismien tutkimuksessa, mutta vielä ei kuitenkaan tiedetä, miten aksolotlit ylläpitävät regeneraatiokykyään. Nisäkkäillä kyky korjata vaurioituneita kudoksia heikkenee merkittävästi iän myötä, johtuen osittain senesenttien solujen kertymisestä kudoksiin. Aksolotleilla puolestaan senesenttien solujen määrä ei iän myötä nouse. Vähäisen senesenssin on esitetty tukevan aksolotlien läpi elämän säilyvää regeneraatiokykyä. Aksolotlit kykenevät tehokkaasti poistamaan senesenttejä soluja, mutta ei tiedetä, kykenevätkö ne lisäksi estämään senesenssin käynnistymistä. Tämä opinnäytetyö tarjoaa ensimmäisen osoituksen aksolotlin soluista erittyvästä senesenssin vastaisesta aktiivisuudesta. Tämän työn perusteella viljeltyjen aksolotlisolujen kasvatusliuokseensa erittämät tekijät vähentävät senesenssiä ja lisäävät solujen jakautumista hiiren alkion fibroblasteissa, joita käytetään yleisesti mallintamaan spontaania senesenssiä. Muiden tutkittujen solutyyppien, kohdunkaulansyöpäsolujen ja nuorten hiiren alkion fibroblastien, kasvatusliuokseensa erittämät tekijät puolestaan eivät juurikaan vähentäneet senesenssiä, vaikka ne lisäsivätkin merkittävästi solujen jakautumista. Tämän perusteella aksolotlisoluista erittyvät tekijät näyttävät vähentävän senesenssiä suoraan, eikä vain pelkästään lisäämällä solujen jakautumista. Näiden havaintojen pohjalta voidaan tulevaisuudessa pyrkiä määrittämään edistääkö senesenssin estäminen regeneraatiota in vivo.

Intestinal epithelium is capable of rapid regeneration, which is associated with transient changes in cellular identity. Some of these changes involve an enrichment of fetal-like gene expression and simultaneous suppression of adult stem cell signature. Interestingly, the upregulation of fetal-like marker Stem cell antigen 1 (Sca1) is modulated by extracellular matrix (ECM) which is known to guide epithelial cells during regeneration. Our recently published decellularized small intestinal ECM (iECM) system retains the composition and topology of natural ECM. This makes it an attractive system for ex vivo studies addressing regeneration. This thesis aimed to gain insight into the fetal-like identity and its dynamics using an ex vivo iECM system. Intriguingly, Sca1 expressing cells on iECM displayed migratory features, such as a leading edge and changes in nuclear morphology. Curiously, these features are typical for epithelial cells during development. Furthermore, based on marker gene expression during iECM re-epithelization, fetal-like state was upregulated while adult stem cell state was downregulated, revealing a gradually emerging inverse correlation. Additionally, data suggests that circadian rhythms may have a role in modulating the fetal-like state. iECM from an active-state mice indicated a reduced capability to induce fetal-like identity and overall re-epithelization compared to the rest-state iECM. The results of this thesis suggest further potential of iECM system in studying emergence of fetal-like state during re-epithelization and circadian rhythm impact on it.

This study compared proliferation rate and expression of cardiac stem cell markers in one day seven days old mice hearts (1D and 7D). Primary antibodies Ki-67 and C-kit were used in immunohistochemistry and primers C-kit, GATA-4, Myh6, Sca-1 and Mesp1 were used in quantitative PCR. This study found a considerably higher proliferation rate and a higher number of C-kit+ stem cells in 1D than in 7D samples, but the difference was not statistically significant due to a small sample size. A significant difference in the expression of other studied markers was not found. These findings suggest that a decrease in proliferation rate and the number of C-kit+ stem cells coincide with the loss of regenerative potential. Therefore, it is possible that either, or both, of these changes are responsible for the closure of the regenerative window.

Fire is an important driver of the boreal forest ecosystem, and a useful tool for the restoration of degraded forests. However, we lack knowledge on the ecological processes initiated by prescribed fires, and whether they bring about the desired restoration effects. The purpose of this study was to investigate the impacts of low-intensity experimental prescribed fires on four ecological processes in young commercial Scots pine (Pinus sylvestris) stands eight years after the burning. The processes of interest were tree mortality, dead wood creation, regeneration and fire scar formation. These were inventoried in twelve study plots, which were 30 m x 30 m in size. The plots belonged to two different stand age classes: 30-35 years or 45 years old at the time of burning. The study was partly a follow-up of study plots researched by Sidoroff et al. (2007) one year after burning in 2003. Tree mortality increased from 183 stems ha-1 in 2003 to 259 stems ha-1 in 2010, corresponding to 15 % and 21 % of stem number respectively. Most mortality was experienced in the stands of the younger age class, in smaller diameter classes and among species other than Scots pine. By 2010, the average mortality of Scots pine per plot was 18%, but varied greatly ranging from 0% to 63% of stem number. Delayed mortality, i.e. mortality that occurred between 2 and 8 years after fire, seemed to become more important with increasing diameter. The input of dead wood also varied greatly between plots, from none to 72 m3 ha-1, averaging at 12 m3 ha-1. The amount of fire scarred trees per plot ranged from none to 20 %. Four out of twelve plots (43 %) did not have any fire scars. Scars were on average small: 95% of scars were less than 4 cm in width, and 75% less than 40 cm in length. Owing to the light nature of the fire, the remaining overstorey and thick organic layer, regeneration was poor overall. The abundance of pine and other seedlings indicated a viable seed source existed, but the seedlings failed to establish under dense canopy. The number of saplings ranged from 0 to 12 333 stems ha-1. The results of this study indicate that a low intensity fire does not necessarily initiate the ecological processes of tree mortality, dead wood creation and regeneration in the desired scale. Fire scars, which form the basis of fire dating in fire history studies, did not form in all cases.