Cerebral cortex development is a complex process that integrates both extrinsic and intrinsic mechanisms. The surrounding cellular environment triggers receptor activation, which in turn initiates components of different signalling cascades and subsequently gene transcription, influencing cell survival, proliferation, and differentiation. Genetic mutations causing a loss-of-function or gain-of-function of signalling pathways elements can lead to cortical abnormalities and result in cognitive dysfunctions. In this thesis, I examined the receptor tyrosine kinase (RTK) TrkB and TrkC, the small GTPase Ras, and the C/EBP family of transcription factors, investigating their roles during cerebral cortex development. First, I looked at the role of C/EBPs during cortical cell fate determination. I determined that inhibition of C/EBPs decrease neurogenesis, keeping precursors in an undifferentiated state and later promoting their differentiation into astrocytes, while expression of an activated form of C/EBP promoted neurogenesis and reduced astrogenesis. Moreover, the inhibition of MEK, a mediator of C/EBPβ phosphorylation, also caused a decrease in neurogenesis. Thus, activation of the MEK-C/EBP pathway biases precursor cells to become neurons rather than astrocytes, thereby acting as a differentiation switch. Second, I examined the involvement of Trk signalling during cortical development. I showed that genetic knockdown using shRNA, or inhibition using dominant negative of TrkB and TrkC lead to a decrease in proliferation and later to postnatal precursor cells depletion. Moreover, it caused a reduction in number of neurons combined with mislocalization of the generated neurons to the different cortical layers. Thus, Trk signalling plays an essential role in the regulation of cortical precursor cell proliferation and differentiation during embryonic development. Third, I elucidated the effect of Costello syndrome H-Ras mutations during cerebral cortex formation. I determined that these mutations promoted cell proliferation and astrogenesis, while reducing neurogenesis. Together, these data support a model where proper Trks/Ras/MEK/C/EBP signalling is essential for normal genesis of neurons and astrocytes and show that cortical development perturbations can ultimately lead to cognitive dysfunction as seen in Costello syndrome patients.

<p>Studying the early stages of cancer can provide important insight into the molecular basis of the disease. In many human cancers, such as prostate, pancreatic, and colon cancer, a pre-neoplastic, or intermediate, stage of the disease has been identified. The pre-neoplastic stage is presumed to be a transition during which normal cells undergo malignant transformation. However, the link between the pre-neoplastic cells and end-stage disease has never been formally established. To investigate the fate of such cells, the patched (ptc) mutant mouse, a model for the brain tumor medulloblastoma was used. Pre-neoplastic cells (PNCs) are found in most ptc mutants during early adulthood, but only 15% of these animals develop tumors. Although PNCs are found in mice that develop tumors, the ability of PNCs to give rise to tumors has never been demonstrated directly, and the fate of cells that do not form tumors remains unknown. Genetic fate mapping and orthotopic transplantation provided definitive evidence that PNCs give rise to tumors and showed that the predominant fate of PNCs that do not form tumors is differentiation. Moreover, N-myc, a gene commonly amplified in medulloblastoma, can dramatically alter the fate of PNCs, preventing differentiation and driving progression to tumors. Importantly, N-myc allows PNCs to grow independently of hedgehog signaling, making the resulting tumors resistant to hedgehog antagonists. These studies provide the first direct evidence that PNCs can give rise to tumors, and demonstrate that identification of genetic changes that promote tumor progression is critical for designing effective therapies for cancer.</p> / Dissertation

No description available.

Over the past 2001~2005 years, the ozone concentration of Kaohsiung county had a rising trend year by year. It¡¦s one of the main reasons that air quality was bad in Kaohsiung and Pingtung Counties. In order to reach the purpose to improve the ozone and air quality effectively, we need to make the whole investigation and of the ozone precursors VOCs and NOx. In addition, the ozone concentration is also influenced by factors, such as intensity of sunshine, temperature, humidity, rainfall, and speed of wind direction, etc. This research mainly investigated the distributing of the ozone precursors of the vertical height and the photochemical ozone formation reactivity with sounding for the 22nd ¡Vthe 25th of November in the Lin-Yuan petrochemical industrial park to discuss the relation of synoptic systems and meteorological parameterization, as the reference used in controlling ozone concentration. It is known the comprehensive synoptic systems are Northeasterly Monsoon Winds type by the analysis of the meteorological parameterization. The station of fishers association was the downwind position and the station of sin-yuan elementary school was the upwind position. The sea-land breeze, that is normally low-latitude (under about 700 meters) regional wind or local circulation, causes the position change of upper and lower wind. The whole trend of ozone and speed of wind of the two stations had negative correlation obviously and the correlation was bad for the height under 500 meters. The whole trend of ozone and NMHC was negative correlation in range of 100m to 300m that was better than above 500 meters. The whole trend of ozone and NOx was negative correlation in the height of 100 meters and had no correlation in above 300 meters. It shows that correlation of O3 and NOx is relatived to source of NOx pollution and is decreased with the altitude height.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 78-84). Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 78-84). Also available online.

published_or_final_version / Biochemistry / Master / Master of Medical Sciences

Hepatocellular carcinoma (HCC) is the major type of liver cancer. In Hong Kong, thousands of deaths are related to this disease every year. Hepatitis B virus (HBV) infection is one of the major risk factors of HCC development. The high prevalence of HBV carriers in Southeast Asia including Hong Kong can account for the particularly high HCC cases in these areas. HCC is often asymptomatic. The diagnosis and treatment are often delayed which lead to inapplicable of surgical resection. Meanwhile, conventional treatment regimes such as systemic chemotherapy were found to have limited responses. Hence, the case mortality rate of HCC is the second highest among all the cancers. Granulin-epithelin Precursor (GEP) is a glycoprotein growth factor which regulates multiple cellular functions. Our group has demonstrated that GEP is over-expressed in more than 70% of HCC cases and GEP expression is positively correlated to tumor malignancy. Our group has also verified that suppression of GEP by monoclonal antibody leads to significant inhibition of HCC growth and reduction of malignancy. Therefore, GEP has the potential to be a novel therapeutic target of HCC. MicroRNAs (miRNAs) are short non-coding RNAs that regulate mRNA translation. Previous studies showed that miRNA dys- regulation is closely associated with HCC progression and the high stability of miRNAs allows them to be cancer biomarkers or therapeutic targets. This project aims to investigate the miRNAs that regulate GEP and their functions in HCC. Potential GEP-regulating miRNAs were identified by literature review and in silico prediction by bioinformatics tools. MiR-615-5p, miR-588, miR-29b, miR-195, and miR-659 were identified as the potential candidates. Quantitative polymerase chain reaction (qPCR) was utilized to examine the miRNAs’ expressions in HCC clinical samples. Only miR-29b and miR-195 were detected and hence they were selected for further study. Our results showed that miR-29b and miR-195 expression levels were significantly decreased in HCC comparing to adjacent non‐tumor tissue (P<0.001) in more than 70% of cases. MiR‐195 and miR‐29b were over‐expressed in Hep3B HCC cell lines by miRNA mimics and GEP protein level was significantly suppressed after miR-29b mimic transfection. The transcript level of GEP was found to be unchanged after the miR‐29b over-expression. This suggests miR‐29b does not regulate GEP protein expression by mRNA degradation. The effects of miR‐195 and miR‐29b on HCC proliferation were also examined. The growths of HCC cells were suppressed notably after over-expression of miR‐195 (P<0.005) and miR‐29b (P<0.005) respectively. In conclusion, miR‐195 and miR‐29b are frequently down-regulated in HCC. MiR‐29b can negatively regulate GEP expression and does not interfere with GEP mRNA level. Furthermore, miR‐195 and miR-29b can function to inhibit HCC cell growth significantly. / published_or_final_version / Surgery / Master / Master of Philosophy

<p>Medulloblastoma is the most common malignant brain tumor in children. The understanding of the genetic alterations in this tumor is emergent, and many such genetic driver events have yet to be functionally-characterized. Our studies have sought to understand the causes and consequences of OTX2 dysregulation in established medulloblastomas and in its putative cellular origins. Using a tumor genetic approach, we have uncovered frequent OTX2 copy number gains driving expression of this oncogene in a subset of medulloblastomas. However, OTX2 is frequently expressed in medulloblastomas independent of genomic copy number gain, and we thus sought to understand the transcriptional regulation of this gene in these tumors. We have found that chromatin accessibility, promoter DNA methylation, and activity of a distal downstream enhancer is distinct between OTX2-expressing and -nonexpressing medulloblastomas. Notably, autoregulation serves to maintain OTX2 expression in some medulloblastomas, whereas DNA methylation actively suppresses OTX2 in tumors not expressing this gene. Finally, we describe the effect of expressing Otx2 (the mouse homolog of OTX2) aberrantly in the developing mouse hindbrain, revealing that Otx2 disrupts spatiotemporal restrictions of neuronal progenitor cell proliferation. The effect of Otx2 in vivo is transient, with ectopically-proliferating cells give way to differentiated neurons. We found that OTX2 expression was not able to give rise to high penetrance medulloblastoma when combined with P53 deletion or double heterozygosity for P53 and PTEN. Thus, although Otx2 alters migration and proliferation dynamics of hindbrain neuronal progenitor cells, further studies are needed to identify the genetic alterations that cooperate with this oncogene to give rise to medulloblastoma.</p> / Dissertation

Optical precursor is the sharp optical pulse front that does not show delay in absorptive media. In this thesis, optical precursor behavior in rubidium (Rb) vapor was investigated in the picoseconds regime. An amplified femtosecond laser was shaped to a 7-ps square pulse with sharp rising and trailing edges. This pulse was then sent into a hot rubidium vapor, and the center frequency of the laser pulse was absorbed. The output pulses were measured by a fast streak camera with 2-picosecond resolution. By varying the temperature of the Rb vapor, the measured pulse shapes showed the progression of formation of optical precursors. The measured pulses shapes showed good agreement with theory. On the other hand, a connection between optical precursors and femtosecond laser pumped 3-photon superradiance was investigated in this thesis. Maxwell-Bloch equations were numerically solved in two steps with commercial software Mathematica 8. A good agreement was found between simulation and experiment. It was confirmed that, at low excitation regime, superradiance generated from hot rubidium vapor, which were pumped by a femtosecond laser, can be understood as the formation of optical precursors.