Personnel
Lab Members
Swanson Lab - August 2006 (L to R standing) Eric Levinsohn, William Feliciano, Suresh Mohan, Peter Beemiller, Youxhin Zhang, Sam Straight, Jonathan Levinsohn, Sei Yoshida, Adam Hoppe (L to R Seated) Stephanie Seveau, Lynn Kamen, Joel Swanson, Mike Davis, Lee Shaughnessy

 Current Members:

 

Michael Davis

William Feliciano
Cellular and Molecular Biology Graduate Program

Abstract:
Involvement of Rab5 in vacuole maturation in activated macrophages
Rab5 is a small GTPase that localizes to early endosomes. It is involved in regulating both the fusion of endocytic vesicles and early endosomes and the homotypic fusion of early endosomes. When in its GTP-bound form, Rab5 is active in membrane fusion. Past work has shown that expression of GTPase-deficient Rab5 mutant induces giant endosomes in cells. On previous work carried out in our laboratory using fluorescent constructs of Rab5 and Ratiometric fluorescence microscopy, we obtained results showing that the maturation pathway of phagosomes in macrophages follows a sequential appearance of proteins actin, Rab5, Rab7 and LAMP1. Ratiometric imaging was used to compare the ratio of YFP to CFP in the whole cell and in the phagosome to obtain average fluorescent intensities. Inhibition of Rab5 or Rab7 was enough to alter the progression of phagosomes to lysosomes which showed the important role of these proteins. Further studies of the role Rab5 during maturation will be carried out using different Rab5 mutants to observe using FRET where exactly the Rab5 activation is occurring. As we understand better the role Rab5 plays during phagosomal maturation, different therapeutic methods can be proposed to control its activity during infections.

Fun Facts:
- Published in Dear Abby once.
- I love animals, if I could do something else it would be wildlife biologist. My heroes are Homer Simpson. In case anyone is interested I do enjoy long walks on the beach.

 

 

Youxin Zhang
Biophysics Graduate Program

Abstract:
Studying signaling coordination during phagocytosis by live cell imaging
Phagocytosis is essential for the clearance of dead cells and infectious agents. Studying the signal transduction process and coordination during phagocytosis is important for understanding infection diseases.  Immunoglobulin G (IgG) Fc receptors (FcγR) are the most extensively studied receptors among different receptors responsible for the internalization by phagocytes. A particle coated with IgG will induce clustering among Fcγ receptors and the phosphorylation of their immunoreceptor tyrosine-based activation motifs (ITAM) by Src family kinases. This stimulation triggers a series of intracellular signals, which lead to cytoskeleton rearrangement, membrane trafficking and degradation of phagosome contents by NADPH oxidase complex. Many signaling molecules, such as Cdc42, Rac, Arf1, Arf6 and phosphoinositide 3’-kinase type IA (PI3K), have been discovered to be involved in this signal pathway. PI3K, which generates phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) from phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), is necessary for phagocytosis of particles whose diameter is larger than 2μm. Two stages of signals during phagocytosis have been identified. Stage 1 signals, such as the activation of Cdc42, are not dependent on PI3K and are sufficient to internalize small particles. Stage 2 signals, such as the activation of Rac2 and the deactivation of Cdc42, are dependent on PI3K and required to internalize particles larger than 2 μm. We are going to try to identify more stage 1 or stage 2 signals according to their dependence on PI3K by ratiometric fluorescence imaging or FRET imaging. In addition, we hypothesize that the magnitude of stage 1 signals is proportional to ligand density on the phagocytosed particle while the magnitude of stage 2 signals are not since they are coordinated over the whole phagosome. We are developing a method for measuring the magnitude of signaling molecule recruitment, based on fluorescence ratiometric imaging.

 

 

 

Samuel Straight, Ph. D.

 

 

 

 

 

 

 

 

Adam D. Hoppe, Ph. D.

Abstract:
Cellular pathways are made up of numerous physical and chemical interactions between proteins. These interactions, mediate diverse events such as signal transduction, regulation of the cytoskeleton and the traffic of membrane. My research focuses on understand how these molecular interactions give rise to the spatial and temporal coordination of these events in living cells. To accomplish this goal, I develop and apply advanced imaging technologies to measure the location and dynamics of direct protein interactions. These technologies primarily take advantage of a physical phenomenon called Fluorescence Resonance Energy Transfer (FRET), which occurs on a length scale similar to that of the diameter of most proteins and can be used to detect the direct binding between two proteins. These approaches include development of both instrumentation and image analysis/image reconstruction algorithms.

My biological focus is to understand how receptors on the surface of the macrophage coordinate rearrangements of the actin cytoskeleton to mediate phagocytosis (internalization of large >1 mm size objects by cells). This process is critical for innate immunity, antigen presentation, and clearance of infections, and is often co-opted by microbes to gain entry into host cells.
Website: http://www.sitemaker.umich.edu/adhoppe/home

 

 

 

Joel Swanson
Principal Investigator

 

Sei Yoshida, Ph. D.

 

 Past Members:

Peter J. Beemiller, Ph. D.

Lee M. Shaughnessy, Ph. D.

Stephanie Seveau, Ph. D.

Lynn Kamen, Ph. D.