Abstracts:
Chu Chen - In mammalian cells, accurate chromosome segregation during mitosis requires that kinetochores of sister chromatids attach to microtubules emanating from opposite spindle poles. In the absence of kinetochore-microtubule attachment, the spindle assembly checkpoint (SAC) is activated to delay anaphase onset. Over the past two decades, researchers have basically revealed the fundamental biochemical pathway of SAC signaling. However, how SAC effectively halts mitosis progression in the presence of very few unattached kinetochores is less addressed. In this talk, quantitative evidence will be presented which suggest the presence of synergistic actions in SAC. Hypothesis about the underlying mechanism and preliminary data from ongoing validation experiments will also be discussed. This cooperativity may enable a single unattached kinetochore to produce a strong enough signal.-

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Hayden Nunley - Many epithelial tissues are composed of several types of cells with distinct functions. For proper functioning of the tissues, it is often important that the different types of cells form a spatial pattern. The specific biological details of how the cells interact to form these patterns are often not fully understood. To study the developmental processes in the absence of detailed biological information, it is useful to test which simplified physical models are consistent with experimental observations. With insights from these models, we identify specific candidate proteins or cellular structures necessary for the interaction, and generate predictions of how specific manipulations will affect tissue patterning. In this spirit, we will discuss the formation of a crystal of cone photoreceptors in juvenile zebrafish retinae. We find that the structure and arrangement of defects in the tissue are consistent with a purely mechanical model in which cones of one specific type interact with other cones of the same type at short range. We identify a specific cellular structure as a candidate for mediating this interaction. We will also discuss neural fate specification in human embryonic stem cell colonies. To study this pattern which has a length scale that does not scale with colony size, we propose a model in which cells respond to mechanical stresses by altering their contractility.