Zhang Jiping. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 157-179). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Adult stem cells are vital to animal biology, tasked with replenishing cells in a variety of tissue types. Historically, there have been two contrasting models of stem cell behavior, “single-cell asymmetry,” where each stem cell is generally long lived and is responsible for perpetual daughter (non-stem) cell production, and “population asymmetry,” where a group of stem cells maintain population numbers while producing non-stem cell daughters, but individual stem cells undergo stochastic competition leading to frequent loss or amplification of individual lineages. Our work examines Drosophila ovarian Follicle Stem Cells (FSCs), which are somatic adult stem cells organized as a population of 14-16 cells within each germarium. FSCs are responsible for the production of two distinct somatic daughter cell types at opposite borders of the stem cell population. The FSCs are arranged in three anteroposterior layers; posterior “layer 1” FSCs divide faster and directly produce Follicle Cells (FCs), while anterior “layer 2 and 3” FSCs divide more slowly and give rise to Escort Cells (ECs). We have examined how signaling pathways contribute individually to FSC behavior, using clonal analysis to manipulate individual FSC genotypes and subsequently determine how autonomous FSC properties and competition among FSCs is affected. Our data indicate that Janus Kinase/Signal Transducers and Activators of Transcription (JAK-STAT) and Wnt pathways are primarily responsible for regulating location, proliferation and differentiation in FSCs. The activities of Hedgehog (Hh), Hippo (Hpo), and Phosphoinositide 3-kinase (PI3K) pathways are also shown to be important for FSC competition.

Huang Hai. / "May 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. (158-183). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Development in shiitake mushroom, Lentinula edodes, is a unique process and studies of the molecular basis of this process may lead to improvement in mushroom cultivation. Previous studies have identified a number of signal transduction genes related to mushroom development, but those genes have not been well characterized. The present work characterized a developmentally regulated MAP kinase, Le.MAPK, Histidine kinase Le.nik1 and their interacting partners in the signal transduction pathways. / Histidine kinase Le.nik1 is the first Histidine kinase gene found in basidiomyces by differential display by RAP-PCR and it has a high sequence homology with the Histidine kinase from C. albicans and B. cinerea, which may be related to development and stress responses. A 7.8kb genomic DNA sequence and the full-length ORF of 6.29kb cDNA sequence of the two-component histidine kinase Le.nik1 has been determined. Northern blot analysis and real time RT-PCR showed that the transcript expression level of Le.nik1 increases from mycelium to mature fruiting body. This suggests that Le.nik1 plays an essential role in fruiting body development. In situ hybridization of different fruiting body stage demonstrated the transcript localization of Le.nik1 in the developing hymenophore and trama cells, which reveals Le.nik1's role in fruiting body development. Real time RT-PCR results suggest the relationship between Le.nik1 and dicarboximide fungicides and oxidant. Yeast two-hybrid studies of Le.nik1 response regulator yields two novel interacting protein and they may also be related to fruit body development as shown by real-time RT-PCR and in situ hybridization. / Le.MAPK gene was isolated and identified by RNA fingerprinting of differentially expressed genes. Le. MAPK shows high sequence identity to the MAP kinase in other fungus includes U. maydis, N. crassa and S. cerevisiae. Le.MAPK was found to be interacting with Le.DRMIP from the yeast two hybrid analyses. Le.DRMIP is a novel gene with a predicted N-terminal mitochondrial signal peptide, suggesting that their interactions relate to the mitochondrial signaling pathway. The expression profiles of these two genes reveal their importance in fruiting body initiation and development; the Le.DRMIP transcript is localized predominantly in the developing young fruit body and gills, which further signifies its role in cell differentiation during mushroom development. These results suggest a model in which Le.MAPK and Le.DRMIP regulate mitochondrial signal transduction during fruit body development in L. edodes. / Through the studies of Le. MAPK and Le.nik1 , this work enhances our knowledge of the role and functions of these signal transduction genes in mushroom development. These studies can also help us to investigate the biological function of these signal transduction genes in fungi and other organisms. / Szeto Ying Ying. / "October 2006." / Adviser: Hoi Shan Kwan. / Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 5750. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 126-139). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

The microtubule-associated protein tau normally functions to bind to and stabilize microtubules. However, evidence now indicates that tau may also play a critical role in signaling pathways linked to neuronal development and neurodegeneration. The tau association with numerous signaling proteins such as tyrosine kinases, adaptor proteins, and scaffold proteins support this hypothesis. Phospho-Y18 tau was previously found in Alzheimer’s disease (AD) brain. Interestingly, this phosphorylation appeared to be regulated during neurodegeneration possibly by a tyrosine phosphatase(s). Identifying a candidate phosphatase, our lab found the association between tau and SHP2 in a neuronal cell line and dephosphorylation of phospho-Y18 by protein tyrosine phosphatase SHP2 in vitro. Since both tau and SHP2 play a critical role in NGF-induced signaling pathway, these findings raised the possibility that the tau-SHP2 association has a role in NGF signaling. The aim of this dissertation research is to characterize the tau-SHP2 association and its role in neuronal signaling. Here, we provide evidence that tau phosphorylation is not required for SHP2 association but significantly enhances the interaction. The SHP2 binding region of tau napped to residues 256-273, which contain the microtubule binding repeat 1 of tau. Using in situ proximity ligation assay (PLA), we also showed the presence of endogenous tau-SHP2 and tau-activated SHP2 complexes in neuronal cells. The number of complexes was increased in the cells in response to NGF. Our PLA data also showed the localization of these complexes to actin ruffles. In NGF signaling, we showed that phosphorylation at T231 of tau was necessary for the increase in tau-SHP2 association. Lastly, we provide evidence that tau-SHP2 complexes are present in mouse primary neuronal cultures and mouse brain sections. Together, these findings show a role for tau phosphorylation in SHP2 binding and a potential role for tau-SHP2 interaction in neuronal signal transduction. Based on our findings, we speculate that there is a role for tau-SHP2 association during early brain development and in neurodegenerative disease.

Bacterial physiology and behavior is controlled by complex regulatory networks. Chemosensory systems are sophisticated signal transduction systems that can govern a range of cellular functions beyond that of traditional flagellar-based chemotaxis. The soil bacterium Myxococcus xanthus encodes eight chemosensory systems regulating multiple behaviors, including motility, exopolysaccharide production, and development. This work characterizes the Che7 system and demonstrates a role for Che7 in coupling aggregation and sporulation during multicellular development. The regulation requires an interaction between a single domain response regulator (CheY7) and a HEAT-repeat protein (Cpc7). A fatty acid desaturase, Des7, also impacts development in concert with the Che7 signaling system. Genetic analysis indicates the target of Che7 regulation is in the heme biosynthesis pathway, which is one aspect of iron homeostasis. Finally, characterization of iron and iron-responsive elements during development reveal a novel regulator, Fur2, that controls timing of development as well as che7 transcription. This work provides expands the known network regulating development in M. xanthus.

The pathogenic bacterium Pseudomonas aeruginosa uses a variety of highly efficient chelating compounds (siderophores) to acquire sufficient iron for growth and virulence. These siderophores can either be endogenous or acquired from exogenous sources such as other bacteria or fungi. The transport of the endogenous siderophore pyoverdine activates a signal-transduction pathway that increases the synthesis of both the ferripyoverdine receptor protein (FpvA) and pyoverdine itself. Signal-transduction systems similar to this have three specific proteins involved: a receptor protein specific for one siderophore in the outer membrane, an anti-sigma factor in the cytoplasmic membrane and a sigma factor that activates gene expression in the cytoplasm. The aim of the research presented in this thesis was to study the roles of the proteins in three different iron uptake and signalling pathways of P. aeruginosa. The substrates for each receptor protein were confirmed and the roles of each protein in the pathways were compared to the P. aeruginosa pyoverdine signalling pathway. The pyoverdine, desferrioxamine and ferrichrome transport pathways were studied to find whether interactions occur between them and if so, the mechanism(s) for that interaction. Furthermore, a technique for analysing gene expression of P. aeruginosa in sputum from the cystic fibrosis (CF) lung was developed. This technique was subsequently used to study the levels of iron responsive gene expression. The receptor, sigma factor and anti-sigma factors were all found to have a role in the siderophore-induced expression of their own signalling pathway. The experimental data provide evidence of similarities in the roles of the sigma and receptor proteins within each pathway but different roles for the anti-sigma factors. In the absence of the cognate sigma factor or anti-sigma factor the expression of the desferrioxamine and ferrichrome receptors could not be upregulated. Without its cognate sigma factor fpvA could no longer be upregulated in the presence of pyoverdine. However, unlike the other systems, in the absence of the cognate anti-sigma factor, expression of fpvA was always observed. This is consistent with the anti-sigma factors being required for the activity of the cognate sigma factor in the ferrichrome and desferrioxamine signalling pathways but not the pyoverdine signalling pathway. The siderophore signalling pathways were found to be upregulated in the presence of multiple siderophores, but generally to a lesser extent than if only one siderophore was available. This suggests that in the presence of multiple siderophores, P. aeruginosa uses all available iron chelators. The study of the role of the receptor, sigma factor and anti-sigma factor into these effects indicate sigma factor competition for RNA polymerase has a major role in the effects of multiple siderophores on pathways upregulation. The gene expression studies of P. aeruginosa in sputum from the lungs of CF patients provided support for the hypothesis that the bacteria were growing in an environment where iron levels were sufficient for bacterial growth, but not storage of iron. The expression of the sigma factor gene pvdS that is required for pyoverdine synthesis was studied because expression of this gene is a sensitive reporter of intracellular iron levels. It was found to be downregulated in bacteria in sputum compared to laboratory grown bacteria. This result suggests the bacteria are inhabiting a more iron-replete environment within the lung. This finding advances our understanding of the CF lung environment and the impact it has on P. aeruginosa infection. This knowledge has medical implications for the development of novel therapies to combat P. aeruginosa infection.

Graduation date: 2006

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 213-239). Also available in electronic version.

Growth and proliferation are normal functions of cells mediated in part via receptor tyrosine kinases such as the epidermal growth factor (EGF) receptor (EGFR). The EGFR binds the extracellular signaling ligand EGF and transduces the signal into the cell. Phosphatidylinositol 3'-kinase (PI3K) responds to EGFR activation and initiates downstream signaling cascades responsible for cell cycle entry, proliferation and inhibition of apoptosis. Cell cycle arrest is required to stop cell growth and proliferation as well as allow apoptosis, if required. The phosphatase and tensin homologue deleted on chromosome ten (PTEN) directly opposes PI3K signaling since its substrate is the PI3K product phosphatidylinositol 3,4,5-trisphosphate. PI3K is a heterodimer composed of a p85 regulatory subunit and a p110 catalytic subunit. PTEN is an essential tumor suppressor protein. Absence of PTEN has been associated with several types of cancer. <p>Our laboratory has characterized new specialized functions for the p85 protein. One function discovered was the ability of p85 to enhance PTEN lipid phosphatase activity. In this thesis PTEN activity is shown to be enhanced at least 3.5 fold in vitro by an equimolar amount of p85. <p>We performed an analysis of PTEN using seven PTEN mutants. Two types of mutants were created: i) regulatory or possible regulatory phosphorylation sites were substituted to mimic both phosphorylated and non-phosphorylated states and ii) alanine substitution of basic amino acid residues. The phosphorylation sites altered were the casein kinase 2 phosphorylation sites in the regulatory domain and tyrosine 336, a proposed regulatory phosphorylation site. Three mutants involving alanine substitution for basic amino acid residues included one mutant in the PASE domain and two more mutants in the C2 domain. It was observed that GFP-PTEN translocates to the plasma membrane upon EGF stimulation. The mimic of constitutive phosphorylation of the Casein kinase 2 sites resulted in cytoplasmic localization whereas the non-phosphorylated mimic was plasma membrane localized regardless of EGFR activation status. Neutralization of positive charge in the PASE and C2 domains seriously impeded the ability of PTEN to bind to phosphorylated phosphatidylinositol lipids and abolished the ability of the protein to translocate to the plasma membrane in response to receptor activation. Located within a cluster of positively charged lysine residues in the C2 domain is a potential phosphorylation site at tyrosine 336. The phosphorylation mimic showed decreased binding to some membrane lipids compared to the non-phosphorylated mimic. The results we generated are consistent with a current model for PTEN regulation that proposes PTEN is localized to the cytoplasm in quiescent cells and dephosphorylation of the regulatory domain occurs upon EGF stimulation allowing translocation to the plasma membrane. The model proposes that dephosphorylation of the casein kinase 2 sites unmasks regions of positive charge that interact with the anionic plasma membrane. Furthermore, the results suggested that at the plasma membrane p85 interacts with PTEN to increase lipid phosphatase activity and may be involved in targeting PTEN to the activated receptor where PI3,4,5P3 lipids are being produced.