To investigate how cytoplasmic dynein orients the mitotic spindle, we are using the budding yeast S. cerevisiae as a model cell system. This system offers facile genetics, ease of protein manipulation, and a simple astral microtubule organization enabling the dissection of dynein regulation during asymmetric cell divisions, which provides physiological relevance to human stem cell biology, development, and cancer. In previous studies, we found that dynein is targeted to the dynamic astral microtubule plus ends and is delivered via tip-tracking to its cortical anchoring protein, Num1. At the cortex, dynein uses its minus end-directed motor activity to pull an astral microtubule and the connected spindle toward the site of dynein anchorage. We discovered the critical domain in Num1 responsible for dynein interaction and function, and found She1 as a potent inhibitor of dynein motility along the astral microtubules. We will investigate how these cortical and microtubule-associated components mediate spatial and temporal regulation of dynein activity, thereby ensuring directional spindle movement into the yeast bud cell.
Aim 1. Identify the mechanism responsible for dynein inhibition along astral microtubules. To dissect the molecular basis of She1-mediated dynein regulation, we will determine how She1 interacts with dynein and analyze the subcellular localization of She1, testing the hypothesis that it is asymmetrically targeted to different areas of the cell to restrict dynein activity. We will search for specific Sh1 binding partners, investigate the functional roles of these proteins, and test the significance of their interactions with She1.
Aim 2. Determine the effect of dynein-cortex interaction on dynein motility. We hypothesize that cortical Num1 enhances dynein motility enabling dynein-dynactin to pull the mitotic spindle into the narrow bud neck. Using multiple approaches encompassing biochemistry, genetics, and in vitro single-molecule motility assays, we will dissect the molecular basis underlying the interaction between dynein, dynactin, and Num1. We will investigate the potential roles of Num1 in triggering dynein offloading or stimulating dynein minus end-directed motility.
This research will help us understand the cellular pathways that regulate the basic functions of an ancient motor molecule called cytoplasmic dynein. In humans, this motor has many critical physiological roles ranging from maintaining healthy tissue integrity to ensuring proper divisions of many cell types including stem cells. The information obtained from this research may serve as the basis for the development of new therapies, since defects in the latter role have been linked to the genesis of abnormal divisions in cancer tissues.
|Zhu, Yili; Lee, Wei-Lih (2014) The role of +TIPs in directional tip expansion. Mol Microbiol 94:486-9|
|Markus, Steven M; Kalutkiewicz, Katelyn A; Lee, Wei-Lih (2012) Astral microtubule asymmetry provides directional cues for spindle positioning in budding yeast. Exp Cell Res 318:1400-6|
|Tang, Xianying; Germain, Bryan St; Lee, Wei-Lih (2012) A novel patch assembly domain in Num1 mediates dynein anchoring at the cortex during spindle positioning. J Cell Biol 196:743-56|
|Markus, Steven M; Plevock, Karen M; St Germain, Bryan J et al. (2011) Quantitative analysis of Pac1/LIS1-mediated dynein targeting: Implications for regulation of dynein activity in budding yeast. Cytoskeleton (Hoboken) 68:157-74|
|Markus, Steven M; Lee, Wei-Lih (2011) Regulated offloading of cytoplasmic dynein from microtubule plus ends to the cortex. Dev Cell 20:639-51|
|Wadsworth, Patricia; Lee, Wei-Lih; Murata, Takashi et al. (2011) Variations on theme: spindle assembly in diverse cells. Protoplasma 248:439-46|
|Ferenz, Nick P; Ma, Nan; Lee, Wei-Lih et al. (2010) Imaging protein dynamics in live mitotic cells. Methods 51:193-6|
|Lee, Wei-Lih; Wadsworth, Patricia (2009) New spindle morphogenesis model by Dynein, Nudel, and the spindle matrix. Cell Res 19:529-31|
|Tang, Xianying; Punch, Jesse J; Lee, Wei-Lih (2009) A CAAX motif can compensate for the PH domain of Num1 for cortical dynein attachment. Cell Cycle 8:3182-90|
|Markus, Steven M; Punch, Jesse J; Lee, Wei-Lih (2009) Motor- and tail-dependent targeting of dynein to microtubule plus ends and the cell cortex. Curr Biol 19:196-205|
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