AbstractsBiology & Animal Science

Microtubules are tubular polymers that are involved in a variety of cellular processes such as cell movement, mitosis and intracellular transport. The dynamic behavior of microtubules makes this possible because all of these processes require quick responses. Embryonic stem (ES) cells were first isolated from mouse embryos and they have two unique characteristics; they can be kept undifferentiated for many passages with a stable karyotype and they can be differentiated into any type of cells under appropriate conditions. The pluripotency of ES cells, their ease of manipulation in culture, and their ability to contribute to the mouse germ-line provides us a model of differentiation both in vitro and in vivo. In my thesis I focused on the cell division and neuronal differentiation of ES cells and developed two methods to understand the effects of microtubule dynamics in spindle assembly and chromosome segregation and to reveal the roles of different Microtubule Associated Proteins (MAPs) in the neuronal morphology formation. In the first part, we developed a live-cell imaging method for ES cells to visualize, track and analyze the single cell behavior in a cell population over a time period. So far many techniques have been adapted and combined for imaging of cell lines, mainly for the cancer or immortalized ones. However, because ES cells are very prone to apoptosis, tend to form spheres and hard to stably label, it is quite tricky to image them in culture conditions. In our system, we combined the BAC-based gene expression with wide-field deconvolution microscopy for ES cells that are plated onto the laminin-511 coated surface and kept in CO2 independent culture conditions. This combined technique does not interfere with the growth of cells and keeps them healthy up to 24 hours on the microscope stage. In the second part, we analyzed the effects of MAPs chTOG, EB1, Kif18A and MCAK in the overall spindle morphology and mitotic progression in mES cells. For this purpose, we utilized our stable TUBB-GFP and H2A-GFP cell lines along with our live-cell imaging set-up to reveal the effects of the above-mentioned proteins and the interplay among each other. By using RNAi method we either single or co-depleted the genes by siRNAs and measured the spindle length and width in RNAi conditions. We further analyzed the mitotic progression in H2A-GFP cell line in terms of the metaphase timing and the percentage of chromosome segregation errors. Our results showed that, EB1 depletion did not cause any significant changes in the overall spindle morphology or in the metaphase timing. However, the co-depletion of EB1 with chTOG partially rescued the sichTOG specific mini-spindle phenotype. siKif18A produced longer spindles without any change in the spindle width. Surprisingly, the co-depletion of antagonistic chTOG and Kif18A proteins had additive effects on the spindle dynamics and on mitotic progression in a way that spindle assembly was severely disrupted by the absence of these two proteins and as a result of this, both…