Relevant Degree Programs
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Mar 2019)
No abstract available.
Gap junctions are unique intercellular channels assembled from the canonical gap junction family, connexins (Cxs). These channels connect the cytosols of adjacent cells, allowing direct passages of small ions and molecules for intercellular communication and homeostasis within tissues. A novel family of gap junction proteins, pannexins (Panxs), with low sequence similarity to the invertebrate gap junctions, innexins, was recently discovered in chordates. Similar to Cxs, Panxs are also capable of forming functional hemichannels as well as intercellular channels. Aberrations in gap junctions have been associated with abnormal CNS development and diseases including gliomas. The main purpose of this thesis was to determine if Panxs play a functional role under pathological and normal CNS conditions, each of which is represented by gliomas and neuronal differentiation, respectively. A loss of Panx expression was found in the C6 glioma cell line when compared to its normal counterparts, primary astrocytes. Restoring Panx1 and Panx2 expression in C6 glioma cells by stable transfection induced a dramatically flattened morphology, which is similar to the flat and polygonal shape of cultured astrocytes. Both Panx1 and Panx2 also significantly suppressed the neoplastic phenotype of C6 glioma cells, including in vitro monolayer growth, anchorage-independent growth, and in vivo tumorigenesis in immunodeficient mice. Interestingly, while Panx1 reduced cell motility in C6 glioma cells, Panx2 did not elicit a similar effect. Panx1 and Panx2 exhibited a distinct subcellular localization. Panx1 was detected at the plasma membrane and perinuclear regions, whereas Panx2 was only found in membrane-bound compartments within the cytosol, hence suggesting mechanistically different tumor-suppressive pathways employed by the two Panxs. Furthermore, it was determined that Panx1 and Panx3, but not Panx2, increased neurite numbers and further enhanced neurite outgrowth in PC12 cells during nerve growth factor-induced neuronal differentiation. In conclusion, findings from this thesis suggest a functional role of Panxs in normal and pathological conditions of the CNS, and merit critical future investigations to explore their underlying mechanisms and therapeutic implication in diseases.
No abstract available.
Master's Student Supervision (2010-2017)
Much of the vertebrate skeleton is formed through endochondral ossification. In this process, a chondrogenic template is laid down, which is subsequently replaced by bone. The first step involves condensation of mesenchymal cells and their differentiation into chondroblasts that initiate elaboration of the chondrogenic template. At later stages, chondrocytes undergo hypertrophy, and produce a matrix for bone formation. To enhance our understanding of molecular programs regulating this process a chemical genetics approach was employed. Our strategies involved the development of screens using primary cultures of murine limb bud-derived mesenchymal (PLM) cells. Chondroblast differentiation is associated with increased SOX5, 6 and 9 activity; while hypertrophic differentiation is associated with reduced SOX5, 6 and 9 activity. Therefore, a SOX5/6/9-responsive reporter gene was used to follow expression of the chondroblast phenotype. Compound libraries representing more than 1400 compounds were screened; 28 compounds were found to increase reporter gene activity greater than 2.5 fold. In secondary screens, 7 of 28 positive compounds stimulated cartilage formation, as assessed by alcian blue staining. Two compounds identified, Butamben (butyl 4-aminobenzoate; BAB) and Phenazopyridine hydrochloride (PHCl), exhibited strong pro-chondrogenic activity and morphologically similar alcian blue staining. BAB is a member of the benzocaine family of analgesics and functions by inhibiting sodium channel activity. However, BAB has also been shown to have potassium channel-blocking activity. Specifically, BAB inhibits the activity of Kcnd2; which through transcriptional profiling was also found to be down-regulated by bone morphogenetic protein-4 (BMP4). We speculated BAB and PHCl may be able to modulate chondrogenesis by acting on potassium channels. To confirm this idea we examined molecular activities of PLM cultures treated with BAB and PHCl at two stages of chondrogenesis: 1. pre-chondrocyte to chondroblast and 2. chondrocyte to hypertrophic chondrocyte. Results confirm, BAB and PHCl increase expression of chondrogenic markers and reduce expression of hypertrophic markers. In addition patch clamp analysis revealed both BAB and PHCl are able to block, at least partially, KCND2 channel activity. We confirmed the dynamic expression pattern of Kcnd2 by qPCR and radioactive section in situ hybridization. Together, these results reveal an unanticipated and novel role for Kcnd2 in chondrogenesis.