Jeannette Kunz, Ph.D.

Assistant Professor

Education
Ph.D., Biozentrum, University of Basel, Switzerland
Postdoctoral, University of Wisconsin-Madison

E-mail: jkunz@bcm.edu
Telephone: 713-798-5797
Fax: 713-798-3475

Research Focus

Regulation of actin dynamics in cell movement and morphogenesis.

Actin-driven cell polarization and cell motility play central roles during embryonic development, the wiring of the nervous system, the immune response, and in the metastatic behavior of cancer cells. The polymerization of actin into filaments is tightly regulated in response to extracellular stimuli, both spatially and temporarily within individual cells. The lipid second messenger phosphatidylinositol-4,5-bisphosphate (PI4,5P₂) has emerged as a key signal transducer that links cell surface receptors to the actin cytoskeleton. PI4,5P₂ synthesis promotes actin assembly and is locally upregulated at specific membrane domains by mechanisms that remain largely unknown. Our goal is to elucidate the regulatory circuitry that controls PI4,5P₂ synthesis and to identify the molecular targets of PI4,5P₂ that mediate localized actin assembly. Our research is focused on studying the role and regulation of PI4,5P₂ in mediating the cytoskeletal dynamics required for cell movement and morphogenesis using three model systems: mammalian tissue culture cells, vertebrate neurons and yeast. We use a variety of approaches including genetics, biochemistry, cell biology, and high-resolution microscopy to address these questions. Knowledge of the molecular mechanisms that govern actin assembly during morphogenesis and motility are of importance to normal physiological functions and may also lead to better treatments for diseases such as the spread of cancer and pathological neurological conditions.

Current Projects:

Regulation of actin dynamics during chemotaxis in human cancer cells
Directional cell motility in mammalian cells requires the spatially regulated assembly of actin filaments at the leading edge in response to chemotactic gradients. We found that PI4,5P₂ synthesis is specifically upregulated at the leading edge in migrating cells. We therefore hypothesize that local changes in PI4,5P₂ levels mediate the local cytoskeletal rearrangements during cell migration. In order to test this hypothesis we study the phosphatidylinositol phosphate (PIP) kinases that produce PI4,5P₂. We found that the three PIP kinase isoforms exhibit distinct subcellular localization to lamellipodia, focal adhesions and vesicular structures in mammalian cells. In addition, these isoforms differ in their interaction with regulatory factors. We thus hypothesize that these enzymes respond to distinct stimuli to regulate different cellular functions. We are using RNA interference and dominant-negative approaches to specifically abolish the function of individual isoforms and analyze the effects on actin assembly, leading edge formation, and chemotaxis. These studies will further our understanding of the molecular mechanisms that control actin dynamics during cell movement.
PI4,5P₂regulation of actin dynamics during polarized growth
The pathway for PI4,5P₂ synthesis is conserved between yeast and vertebrates making yeast an ideal model organism to study PI4,5P₂ signaling mechanisms and to identify novel PI4,5P₂ effectors that mediate actin polymerization. Polarized morphogenesis in yeast is dependent on the localized reorganization of the actin cytoskeleton in response to spatial cues. Recent work has identified the yeast formins (Bni1p and Bnr1p) as key components in the assembly of the filamentous actin cables that mediate polarized growth. We found that mutations that abolish PI4,5P₂ synthesis abrogate actin cable formation and cause defects in polarized growth. Our current studies focus on the potential role of PI4,5P₂ in the activation of Bni1p and Bnr1p and on the function of two novel PI4,5P₂ binding proteins required for polarized distribution of actin cables. Since formin proteins are evolutionarily conserved, the results obtained from the studies on the yeast actin cytoskeleton will be informative to more complex eukaryotes including humans.
PI4,5P₂ synthesis and actin dynamics in dendritic spines and synaptic plasticity
Dendritic spines are actin-rich protrusions that are thought to be the primary sites of synaptic plasticity in the brain. The rapid cytoskeletal rearrangements induced in response to synaptic activity are associated with morphological changes in spine shape that may form the basis for long-term memory storage. In collaboration with Gang-Yi Wu’s Group in the department we are testing the hypothesis that local changes in PI4,5P₂ levels drive the temporal and spatial reorganization of the actin cytoskeleton in dendritic spines. This hypothesis is based on our findings from yeast and tissue culture models. We use expression of fusion proteins of GFP to PH domains, which specifically recognize PI4,5P₂, and to actin to visualize real-time changes in PI4,5P₂ levels and actin dynamics in response to synaptic transmission in single hippocampal neurons. Furthermore, we are testing the consequences of up- and downregulating the activity of PIP kinases on dendritic spine morphology and synaptic plasticity. This research will provide essential new insights into the regulation of morphological changes, specifically in dendritic spines, during neuron development and in response to neuronal activity.