Physics Colloquium - Friday, Nov. 2nd, 2007, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Darryl Kropf
Department of Biology
University of Utah

Polarity establishment and asymmetric division in fertilized eggs

The establishment of cellular polarity followed by asymmetric division is fundamental to development in multicellular organisms. This process generates distinct cell lineages that acquire unique cell fates. We are interested in the cellular and physiological mechanisms that control cell polarity and asymmetric division. Fertilized eggs of the brown alga Silvetia compressa offer several advantages for our studies, including the ease of harvesting large numbers of zygotes and the ability to polarize populations using external cues (e. g. light). Our work has focused on the roles of cytoskeleton and endomembranes in establishing a rhizoid/thallus growth axis and in asymmetric division. We find that polarization depends on a dynamic actin array that localizes to the rhizoid pole and serves as a target site for vesicle secretion and endomembrane cycling. This leads to localized growth at the rhizoid pole. Although microtubules are not required for polarization or growth, they organize polar endomembrane arrays and thereby determine growth morphology. In addition, microtubules are critical for correctly positioning the spindle transverse to the growth axis, and for effecting cytokinesis. Recently, we have begun to investigate signaling to the cytoskeleton and results indicate that phospholipid signaling through phosphatidic acid regulates microtubule arrays throughout early development. Our current working model integrating these cellular parameters will be presented.