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Vol. 18, Issue 7, 2542-2560, July 2007

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Sequential and Distinct Roles of the Cadherin Domain-containing Protein Axl2p in Cell Polarization in Yeast Cell Cycle

Xiang-Dong Gao^*,, Lauren M. Sperber^*, Steven A. Kane^*, Zongtian Tong^*, Amy Hin Yan Tong, Charles Boone, and Erfei Bi^*

*Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058; and Banting and Best Department of Medical Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada

Submitted September 18, 2006; Revised April 10, 2007; Accepted April 18, 2007
Monitoring Editor: Tim Stearns

Polarization of cell growth along a defined axis is essential for the generation of cell and tissue polarity. In the budding yeast Saccharomyces cerevisiae, Axl2p plays an essential role in polarity-axis determination, or more specifically, axial budding in MATa or cells. Axl2p is a type I membrane glycoprotein containing four cadherin-like motifs in its extracellular domain. However, it is not known when and how Axl2p functions together with other components of the axial landmark, such as Bud3p and Bud4p, to direct axial budding. Here, we show that the recruitment of Axl2p to the bud neck after S/G2 phase of the cell cycle depends on Bud3p and Bud4p. This recruitment is mediated via an interaction between Bud4p and the central region of the Axl2p cytoplasmic tail. This region of Axl2p, together with its N-terminal region and its transmembrane domain, is sufficient for axial budding. In addition, our work demonstrates a previously unappreciated role for Axl2p. Axl2p interacts with Cdc42p and other polarity-establishment proteins, and it regulates septin organization in late G1 independently of its role in polarity-axis determination. Together, these results suggest that Axl2p plays sequential and distinct roles in the regulation of cellular morphogenesis in yeast cell cycle.

Present address: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.

Address correspondence to: Erfei Bi (ebi{at}mail.med.upenn.edu)