Erfei Bi, Ph.D.
Associate Professor, Dept of Cell & Developmental Biology

Cell Biology and Physiology Program

Address

EDUCATION

Wuhan University: BS (Microbiology), 1985.

University of Kansas Medical Center: PhD (Bacterial Genetics and Cell Biology), 1991.

University of North Carolina : Postdoctoral Research (Yeast Genetics and Cell Biology), 1997.

Research Interests

• Development of cell polarity and control of cytokinesis in budding yeast

Key words: Cdc42p signaling, cell polarity, exocytosis, morphogenesis, actin cytoskeleton, septins, and cytokinesis

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Description of Research

Development of cell polarity and control of cytokinesis in budding yeast

Research in the Bi laboratory focuses on two fundamental problems in cell biology: establishment of cell polarity and control of cytokinesis using the budding yeast Saccharomyces cerevisiae as the model system. Fig. 1. (PDF)

Cell polarization is essential for differentiation and development. In S. cerevisiae, the evolutionarily conserved small GTPase Cdc42p controls the polarized organization of the actin cytoskeleton, which mediates polarized secretion from the Golgi to the plasma membrane (Fig. 1). Currently, we are trying to determine how Cdc42p regulates polarized actin organization in yeast, how different GTPase activating proteins (GAPs) for Cdc42p confer temporal and spatial regulation to Cdc42p, and how the GAPs themselves are regulated in the cell cycle.

The septins are a family of GTP binding, filament forming proteins involved in cytokinesis and other processes. Previously, we hypothesized that the formation of the septin collar at the bud neck involves at least three distinct steps: septin recruitment, ring assembly, and ring maturation into collar (Fig. 1). We have now visualized all three steps in wild type cells by time-lapse microscopy, coupled with 3D image reconstruction. Currently, we are trying to determine how Cdc42p regulates septin organization at the molecular level.

Comparative analysis of cytokinesis in multiple systems including budding yeast, fission yeast, and animal cells indicates that the major proteins involved in cytokinesis are conserved from yeast to mammals, although their organization into the functional machinery that drives cytokinesis and the associated regulatory mechanisms have species specific features.

Fig. 2. Cytokinesis in budding yeast. The actomyosin ring (actin ring plus Myo1p) and secretion (vesicles, indicated by black circles, are transported by a type V myosin Myo2p) both are targeted to the division site in a septin dependent manner.

In S. cerevisiae, cytokinesis is achieved by the coordinated actions of the actomyosin contractile ring (see attached Video. Myo1p GFP contraction) and targeted membrane and cell wall (extracellular matrix) deposition (Fig. 2). Currently, we are trying to determine how Myo1p, the only type II myosin in S. cerevisiae, is targeted to the division site in a septin dependent manner and how the essential light chain for Myo1p as well as other cytokinesis proteins are involved in coordinating the functions of the actomyosin ring and targeted secretion during cytokinesis.

Recent Publications

J. Luo, E.A. Vallen, C. Dravis, S.E. Tcheperegine, B. Drees, and E. Bi. (2004). Identification and functional analysis of the essential and regulatory light chains for the only type II myosin Myo1p in Saccharomyces cerevisiae. J. Cell Biol. 165, 843 855.

S.E. Tcheperegine, X. D. Gao, and E. Bi. (2005). Regulation of cell polarity by interactions of Msb3 and Msb4 with Cdc42 and polarisome components. Mol. Cell. Biol. 25, 6567-8580.

M. Iwase, J. Luo, S. Nagaraj, M. Longtine, H.B. Kim, B.K. Haarer, C. Caruso, Z. Tong, J.R. Pringle, and E. Bi. (2006). Role of a Cdc42p effector pathway in recruitment of the yeast septins to the presumptive bud site. Mol. Biol. Cell, 171110-1125.

X.-D. Gao, L.M. Sperber, S.A. Kane, Z. Tong, A.H.Y. Tong, C. Boone, and E. Bi. 2007. Sequential and distinct roles of the cadherin domain containing protein Alx2p in cell polarization in yeast cell cycle. Mol. Biol. Cell, 18 2542-2560.

H. O. Park and E. Bi. (2007). Central roles of small GTPases in the development of cell polarity in yeast and beyond. Microbiol. Mol. Biol. Rev. 71, 48-96. (Review)

LAB

Rotation Projects:

On cell polarity:

1. Determine how the polarisome, including the Rab GAPs Msb3p and Msb4p, coordinates polarized actin organization and secretion during polarity development.
2. Determine the molecular mechanisms underlying the spatial regulation of the small GTPase Cdc42p by its GAPs.
3. Define the mechanisms by which Cdc42p regulates septin organization.
4. Determine how the septin structures are anchored to the plasma membrane.
5. Determine how Pxl1p, the paxillin like protein in yeast, regulates cell polarity

On cytokinesis:

1. Determine how the type II myosin Myo1p is targeted to the division site in a septin dependent manner.
2. Determine how Mlc1p, the essential light chain (ELC) for Myo1p, coordinates the functions of the type II myosin, type V myosins, and IQGAP during cytokinesis.
3. Define the molecular mechanisms by which the PCH protein Hof1p regulates cytokinesis.
4. Identify novel genes involved in cytokinesis by genetic and biochemical approaches.

Personnel:

Younghoon Oh (Postdoc.)
Zongtian Tong (Thesis Student)
Jennifer Hansen (Thesis Student)
Steve Kane (Research Specialist)
Xiao Dong Fang (Visiting Associate Professor)
Elizabeth Vallen (Visiting Associate Professor)
Jennifer So (Undergraduate student doing Independent Study)