Dahong Zhang

Associate Professor
PhD., University of Massachusetts, Amherst, 1991

Department of Zoology
Cordley 3029
Oregon State University 
Corvallis, OR 97331-2914 

RESEARCH (Supported by ):

I am a cell biologist interested in cellular mechanics of mitosis and cytokinesis and the control of cell cycle. Every time a eukaryotic cell divides, mitosis has to occur accurately to distribute replicated chromosomes to the spindle poles, and cytokinesis has to initiate in the right place to partition segregated chromosomes into the daughter cells. Inaccurate chromosome distribution and uncontrolled cell division may result in cancer and birth defects or other related diseases.

Methods: My laboratory uses biomechanical techniques to investigate mechanisms underlying chromosome movement and cell cleavage. Our basic strategy  is to mechanically dissect and reconstruct spindle apparatus as desired in living grasshopper spermatocytes. The resulting effects on cell division are observed with high-resolution imaging techniques, such as digital-enhanced polarization, DIC, epifluorescence, spinning disc confocal, and conventional confocal microscopy. This strategy simplifies the problem of interest in testing and proposing hypotheses.

Mitosis: Our current focus in mitosis is on chromosome congression, a process that governs movement of partner/sister chromosomes to the spindle equator and ensures equapartition of chromosomes. Failure in chromosome congression due to malorientation or misattachment will lead to either the activation of spindle checkpoint that blocks anaphase chromosome segregation or a disastrous chromosome distribution into the daughter cells. We are interested in how chromosomes know the direction to move and the position to stop in the spindle. We investigate the process by inducing congression with micromanipulation, dissecting directional forces with laser ablations, and revealing force generation with cytoskeleton/motility alterations.

Cytokinesis: Our current focus in cytokinesis is on cleavage induction. Cytokinesis ultimately ensures the proper partition of chromosomes and cytoplasm into the  daughter cells. In animal cells, this is brought about by the formation of a cleavage furrow that bisects the mitotic (or meiotic) spindle between segregated chromosomes. Failure in, or improper positioning of the cleavage furrow makes faithful DNA replication and precise chromosome distribution all for naught. It is known that the mitotic apparatus defines the cell cleavage plane. However, it is not clear how the mitotic apparatus initiates the cleavage furrow due to our lack of in-depth understanding about the source and nature of the furrow signal. Specifically, it is uncertain about which part of mitotic apparatus is the essential source of the signal and whether all parts act in concert. We dissect which spindle constituent is the essential source of furrow signal by testing furrow induction with each single spindle constituent in the absence of all the others.

Chen, W. and D. Zhang (2004) Dynamics and poleward movements of laser-microbeam severed kinetochore microtubule stubs in anaphase. Nature Cell Biol. 6:227-231. 

Alsop, G. B. and D. Zhang (2004) Microtubules continuously dictate distribution of actin filaments and positioning of cell cleavage in grasshopper spermatocytes. J. Cell Sci. 117:1591-1602. 

Alsop, G. B. and D. Zhang (2003) Microtubules are the only structural constituent of the spindle apparatus required for induction of cell cleavage. J. Cell Biol. 162:383-390.

Zhang, D., P. Wadsworth, and P.K. Hepler (1993) Dynamics of microfilaments are similar, but distinct from microtubules during cytokinesis in living plant cells. Cell Motil. Cytoskel. 24:151-155.

Zhang, D., P. Wadsworth, and P.K. Hepler (1992) Modulation of anaphase spindle structure in stamen hair cells of Tradescantia by calcium and related agents. J. Cell Sci. 102:79-89. 

Zhang, D., P. Wadsworth, and P.K. Hepler (1990) Microtubule dynamics in living dividing plant cells: confocal imaging of microinjected fluorescent brain tubulin. Proc. Natl. Acad. Sci. USA. 87:8820-8824. 

Zhang, D., D.A. Callaham, and P.K. Hepler (1990) Regulation of anaphase chromosome motion in Tradescantia stamen hair cells by calcium and related signaling agents. J. Cell Biol. 111:171-182.

TEACHING

BI 460/560. Cell Biology (3)  The course is designed to prepare students for medical, dental, veterinarian, and graduate schools. Topics include chromosome organization, control of gene expression, organelle and protein sorting, vesicular trafficking, endocytosis and protein recycling, cell energetics, cell signaling, cytoskeleton and motility, mechanics of cell division, the cell cycle, and cancer.

BI 461. Cell Biology Laboratory (2) The course comprises intensive hands-on experimental excises presented as mini-research projects. Topics include chloroplast protein isolation/identification, reporter gene expression, salivary chromosome analysis, cytoskeletal transformations, organelle transport, immunocytochemistry of microtubules and microfilaments, and polarizing microscopy of muscle fibers.

MCB 553. Structure and Function of Eukaryotic Cells (3) Examination of molecular and structural elements in eukaryotic cells and their relationship to function. Topics include methods for cellular analysis, membranes, organelles, intracellular sorting, cell signaling, cell motility, and cell division cycle. The course is designed to teach students advanced cell biology along with critical reading and writing skills.

MCB 556/GEN 456/556. Cell Signaling and Development (3) Integrated cellular function in multicellular organisms. Topics include intracellular and cell surface receptors, signaling via cellular mechanics, molecular switches, controls of chromosome distribution and cell division plane selection, tumorigenesis and programmed cell death (apoptosis), development and differentiation in both animals and plants.