Browsing by Subject "neurogenesis"

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.

Angiopoietin 1 (ANGPT1) is an endothelial growth factor and the ligand of the tyrosine endothelial kinase (TEK). The ANGPT-TEK system is known to mediate endothelial cell (EC) interactions and contributes to angiogenesis and vascular remodeling through angiocrine signaling. Although TEK is expressed in neural stem and progenitor cells, a vascular-independent role for ANGPT1 in neurogenesis is still unclear. This study focused on the embryonic expression of angiopoietins and their receptors in wild-type (WT) zebrafish (Danio rerio) and on further characterization of two zebrafish lines: the Angpt1sa14264 line, with a nonsense mutation in the angpt1 gene, and a transgenic line of angpt1 overexpression. Whole-mount in situ hybridization (WISH) and real-time quantitative polymerase chain reaction (RT-qPCR) showed a relatively high expression of angpt1 and tek throughout the first three days of WT development. Imaging of live Angpt1sa14264 and transgenic overexpression embryos revealed the bidirectional effect of angpt1 on the cardiovascular system, suggesting an essential role for normal embryonic development. In the absence of angpt1, gene expression analysis showed a dramatic disturbance in genes involved in neural patterning and neuronal development. The spatiotemporal expression of wingless-type MMTV integration site 1 (wnt1) implicated the midbrain-hindbrain boundary as a major site of Angpt1-mediated regulation of neuronal organization. The downregulated spatiotemporal expression of nestin (nes) indicated a decrease in neural progenitor-like cells throughout the central nervous system (CNS). In the context of angpt1 overexpression, the neurogenic locus notch homolog 1a (notch1a) was slightly increased despite the unchanged expression of all other neuronal markers and neural patterning genes analyzed. The spatiotemporal expression of notch1a was exacerbated in a large cranial vein, albeit detected in typical notch1a domains in the brain. These findings suggest that Angpt1 plays an important role in zebrafish embryogenesis and possibly regulates the organization of the zebrafish midbrain and hindbrain regions.

The aim of this study was to explore the functions of T-type calcium channels, and their possible role in neuronal stem cells migration. The role of T-type calcium channel in mature brain is known to be in producing electroencephalographic oscillations. This action in turn is the key factor in some neuronal physiological and pathophysiological functions, like non-REM sleep, memory, learning and absence epilepsy. In addition, T-type calcium channels have peripheral actions, but this study concerns on its neuronal functions. This low-voltage activated channels functions in neurogenesis is less known than its role in mature brain. It is known to promote neuronal proliferation and differentiation, but what comes to its possible actions in neuronal migration, is poorly studied. This study shows some evidence of T-type calcium channel taking part in neuronal migration in mice embryonic subventricular zones progenitor cells. Selective T-type antagonists, ethosuximide, nickelchloride and a scorpion peptide toxin kurtoxin, decreased the rate of migration in differentiating progenitor cells. This study consists of a literature review and an experimental part. Another aim of this study is to consider an alternative approach to stem cell therapies based on invasive transplantation of the cells. This other attempt is non-invasive manipulating of endogenous stem cells to proliferate and migrate to the injured or depleted area in the brain, differentiate into a desired phenotype and stop their division after they have completed their mission. Non-invasive altering of the stem cells is awaiting pharmacological solutions to resolve the problems being faced in this effort. There are some non-invasive therapies already being used successfully to cure pathological conditions such as spinal cord injury. These methods could be used as well in stem cell based therapies in the treatment of neurodegenerative diseases and brain injuries. These methods are still in the beginning of their way and lacking the full understanding of the key factors that affect neuronal development. These factors include some important endogenous inducing and inhibiting substances. One of the most important inducing substances is calcium ion regulating a variety of events in neurogenesis. T-type calcium channel, as being widely expressed during early brain development, and decaying by neuronal maturation, might have a pivotal role in conducting progenitor cells.