▼ Mitosis ensures the proper segregation of chromosomes into daughter cells, which is accomplished by the mitotic spindle. During fission yeast mitosis, chromosomes establish bi-orientation as the bipolar spindle assembles, meaning that sister kinetochores become attached to microtubules whose growth was initiated by the two sister poles. This process includes mechanisms that correct erroneous attachments made by the kinetochores during the attachment process. This thesis presents a 3D physical model of spindle assembly in a Brownian dynamics-kinetic Monte Carlo simulation framework and a realistic description of the physics of microtubule, kinetochore, and chromosome dynamics, in order to interrogate the dynamics and mechanisms of chromosome bi-orientation and error correction. We have added chromosomes to our previous physical model of spindle assembly, which included microtubules, a spherical nuclear envelope, motor proteins, crosslinking proteins, and spindle pole bodies (centrosomes). In this work, we have explored the mechanical properties of kinetochores and their interactions with microtubules that achieve amphitelic spindle attachments at high frequency. A minimal physical model yields simulations that generate chromosome attachment errors, but resolves them, much as normal chromosomes do. Advisors/Committee Members: Meredith D. Betterton, Matthew A. Glaser, Loren Hough, Thomas Perkins, Richard McIntosh.

▼  Disruption of cilia proteins results in a range of disorders called ciliopathies. However, the mechanism by which cilia dysfunction contributes to disease is not well understood. Intraflagellar transport (IFT) proteins are required for ciliogenesis. They carry ciliary cargo along the microtubule axoneme while riding microtubule motors. Interestingly, IFT proteins localize to spindle poles in non-ciliated, mitotic cells, suggesting a mitotic function for IFT proteins. Based on their role in cilia, we hypothesized that IFT proteins regulate microtubule-based transport during mitotic spindle assembly. Biochemical investigation revealed that in mitotic cells IFT88, IFT57, IFT52, and IFT20 interact with dynein1, a microtubule motor required for spindle pole maturation. Furthermore, IFT88 co-localizes with dynein1 and its mitotic cargo during spindle assembly, suggesting a role for IFT88 in regulating dynein-mediated transport to spindle poles. Based on these results we analyzed spindle poles after IFT protein depletion and found that IFT88 depletion disrupted EB1, γ-tubulin, and astral microtubule arrays at spindle poles. Unlike IFT88, depletion of IFT57, IFT52, or IFT20 did not disrupt spindle poles. Strikingly, the simultaneous depletion of IFT88 and IFT20 rescued the spindle pole disruption caused by IFT88 depletion alone, suggesting a model in which IFT88 negatively regulates IFT20, and IFT20 negatively regulates microtubulebased transport during mitosis. Our work demonstrates for the first time that IFT proteins function with dynein1 in mitosis, and it also raises the important possibility that mitotic defects caused by IFT protein disruption could contribute to the phenotypes associated with ciliopathies. Advisors/Committee Members: Stephen Doxsey, PhD.

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Malignant gliomas are the most common and deadly form of primary brain cancer afflicting adults. Current treatment regimens, including surgical debulking, radiotherapy, and chemotherapy, have limited efficacy, and median patient survival remains only 14 months. Therefore, novel therapies must target different aspects of glioma biology. Two of the most striking features of this cancer are the unusual ability of glioma cells to robustly proliferate and migrate in the brain, and recent evidence suggests that ClC-3, a voltage-gated Cl- channel/transporter is implicated in both of these processes. We hypothesize that ClC-3 may facilitate proliferation and migration by promoting hydrodynamic shape and volume changes; as Cl- efflux occurs, water osmotically leaves the cytoplasm. These shape and volume changes are critical as, for example, a glioma cell divides into 2 daughter cells, or migrates through narrow extracellular spaces in the brain. In this dissertation, we assess upstream signaling to determine how ClC-3 is activated in the context of proliferation and migration. Using a combination of biophysical, biochemical, genetic, and imaging techniques, we identify several mechanisms suggesting that Ca2+/calmodulin-dependent protein kinase (CaMKII) regulates ClC-3 activity. We demonstrate that channels or ligands that increase [Ca2+]i also activate CaMKII, leading to downstream ClC-3 activation and promoting proliferation and migration. CaMKII regulation of ClC-3 is required for a critical cytoplasmic condensation checkpoint at the metaphase-anaphase transition, and inhibition of either protein leads to disrupted volume regulation and proliferation. Additionally, we found that bradykinin, a chemotactic peptide, increases glioma cell migration by activating CaMKII-dependent ClC-3 channels. Inhibition of ClC-3 or CaMKII completely blocked bradykinin-induced migration. We propose that CaMKII activation of ClC-3 is a critical mediator of cellular proliferation and migration and should be integrated into preexisting models. We speculate that [Ca2+]i may be a ""master regulator"" of both proliferation and migration by simultaneously controlling cytoskeletal proteins, kinases, and Ca2+-sensitive ion channels. Finally, our data suggest that targeting Cl- channels or bradykinin receptors on human glioma cells may be a novel therapeutic strategy for the management of malignant gliomas.

PhD

1 online resource (xi, 213 p.) :ill., digital, PDF file.

Neurobiology

Joint Health Sciences

bradykinin cell migration chloride channel ClC-3 Cl- channel

UNRESTRICTED

Advisors/Committee Members: Harald Sontheimer, Bedwell,David Kirk,Kevin Nabors,Burt Wadiche,Jacques.

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The hypothesis that cell volume and the progression of the cell cycle are interdependent has surfaced off and on in the cell cycle literature for the past 30 years. However, a conclusion as to how cell volume is mechanistically involved in cell division has not been reached in mammalian cells. The aim of this dissertation was to establish how volume changes modulate cell cycle progression. Most of the studies addressing this question have examined mass content yet, more recently, focus has been placed on intracellular water, which is determined by the balance between mechanical and osmotic forces. As a result, ion channels and transporters which regulate intracellular osmotic content are integral to the maintenance of cell volume. In this dissertation, I show that a large, rapid and regulated volume decrease occurs as glioma cells progress through mitosis. I refer to this process as pre-mitotic condensation (PMC). This process is functionally linked to DNA condensation prior to cell division as the two events occur simultaneously, and inhibition of PMC results in a prolongation of DNA condensation. Further, my data demonstrates that glioma cells actively accumulate chloride, which acts as the primary energetic driving for cell volume changes in these cells. During the process of PMC, this gradient drives the efflux of chloride through ClC3 channels, which mediates water loss and the volume decrease. Interestingly, chloride accumulation to similar levels can be observed in immature astrocytes and neurons, suggesting that glioma cells recapitulate the biology of immature proliferating cells in the brain. This also suggests that my findings may have broader applicability to cell division in both neural cells and cancer.

xii, 132 p. : ill., digital, PDF file.

Neurobiology

Joint Health Sciences

Voltage Gated Chloride Channels Pre-miotic Condensation DND Condensation C1C3 Mitosis Volume Regulation

UNRESTRICTED

Advisors/Committee Members: Sontheimer, Harald, Bevensee, Mark<br>Engler, Jeffrey<br>Pozzo-Miller, Lucas<br>Theibert, Anne.

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Objetivo: Verificar resposta após debridamento epitelial de córneas humanas. Métodos: Córneas normais foram submetidas a debridamento antes da cirurgia de enucleação. Realizou-se histologia, TUNEL, Ki67, SMA e microscopia eletrônica. Resultados: Seis córneas foram debridadas e preservadas entre ½ e 65 horas, apresentando apoptose nos ceratócitos do estroma anterior. Células estromais em proliferação foram observadas apenas no tempo de 65 horas. Miofibroblastos não foram encontrados. Uma córnea serviu de controle. Conclusões: Os eventos observados em córneas humanas após debridamento epitelial, apoptose e proliferação dos ceratócitos, foram semelhantes aos descritos em animais de experimentação

Purpose: To examine the early wound healing response to epithelial scrape in human corneas. Methods: Normal corneas had epithelial scrape prior to enucleation. Histology, TUNEL assay, Ki67, SMA and transmission electron microscopy were performed. Results: Epithelial scrape was performed in six corneas from ½ to 65 hours prior to preservation. Keratocyte apoptosis was detected in the anterior stroma in all scraped corneas. Keratocyte proliferation was detected exclusively 65 hours after scrape. No myofibroblast was detected. One cornea was not scraped (control). Conclusion: Results obtained in human corneas (keratocyte apoptosis and proliferation) were similar to animal models

Advisors/Committee Members: Alves, Milton Ruiz, Jose, Newton Kara.