Neuroscience Graduate Program at UCSF
Cell-Matrix Signaling in Eye Development
The extracellular matrix (ECM) is a key component of the cellular microenvironment and a driving force in development. Cells as diverse as neurons, stem cells, epithelia and glia, interact with the matrix resulting in localized activation of signaling pathways and cytoskeletal rearrangements. Depending on cell type and context, these interactions drive changes in cell fate, cell migration, and cellular architecture (such as polarization and process extension). Cell-matrix interaction also has a significant impact on the microenvironment itself, and is required for organization of the matrix into specialized basement membranes.
We are interested in identifying the signaling events that translate cell-matrix interaction into cytoskeletal re-arrangements. Loss of this pivotal connection may represent a fundamental defect in the pathology of congenital muscular dystrophy as well as underlie other developmental abnormalities. Importantly, we are interested in studying these signaling events within a physiological context, where the complex interplay between cells and the matrix is preserved in three dimensions as well as in distinct cell types such as neurons and epithelia.
Our current approach is to analyze the function of focal adhesion kinase (and close family member Pyk2) in conditional knockout mouse models as a starting point for understanding the intermediate signaling programs that unite the cell surface with the cytoskeleton. FAK in particular represents a signaling node, and analysis of its function and regulation may provide an important window into cellular function and pathology. We are also addressing other kinases that may regulate cytoskeletal attachment to points of adhesion such as integrin-linked kinase (ILK) and src family kinases (SFK).
Our model system of choice is the developing mammalian eye, given its wide array of cell types and the exquisite interplay of inductive events that drives eye morphogenesis. Furthermore, given its unique accessibility, questions regarding universal mechanisms of development are more easily addressed here, making it an exceptional organ system to draw comparative conclusions about the effect of perturbation of signaling pathways in diverse cell types, as well as the role of microenvironment on cellular fate and activity.
Axonal Pathfinding and Dendritic Tree Arborization
Proper wiring of the visual system requires exquisite regulation of the neuronal cytoskeleton in response to a combination of guidance cues. One project is to examine whether FAK signaling serves as a “molecular switch”, allowing neurons to respond to extracellular signals and dynamically control process extension. The retinal projection is an excellent model system to address this question in vivo.
Retinal ganglion cell axons exit the eye through the optic nerve, cross at the optic chiasm and establish topographic connections onto the thalamus. This connection is translated by thalamic neurons onto their ultimate target in the visual cortex, where visual information is processed. Retinal ganglion cells also elaborate extensive dendritic arbors that are refined postnatally into distinct retinal layers. Since FAK is a critical regulator of neuronal morphology, how does disruption of this pathway impact development of this exquisitely regulated visual system? What extracellular guidance cues (such as netrin, semaphorins or ephrins) impact FAK function? Do these signals collaborate with integrins or activate FAK and related molecules independently? Since all of these neuronal projections are meticulously pruned during development to refine visual acuity, we are also interested in determining in whether FAK/Pyk2 signaling acts together with neuronal activity to control patterning.
The mammalian retina has a striking laminated architecture with neuronal cell types organized into functional layers. How does this pattern form during development? What are the mechanisms that control migration of neuroepithelial precursor/stem cells into their proper position and differentiation into unique cell types with distinct morphology and function?
One research focus of the lab is to address the cellular and molecular mechanisms through which FAK and related molecules control retinal patterning. Our results show that loss of FAK signaling results in lamination defects. Why? Is FAK activity required for proper cell polarity? Differentiation? Migration? Is FAK functioning downstream of integrins or other growth factor or adhesion molecule pathways? One possibility under investigation is that FAK is required for organization of the inner and outer limiting membranes of the retina.
Eye Size, the Lens and Matrix Organization
We have previously shown that FAK is required for organization of the extracellular matrix into basement membranes. It is likely that FAK regulates the linkage between sites of cell-matrix adhesion and the cytoskeleton, although the molecular details of this interaction remain unknown, especially in physiological systems. Another focus of the lab is therefore to investigate this function in a 3D organ system. The mouse ocular lens is a unique and understudied organ that is perfectly suited to study cellular regulation of epithelial cell migration and differentiation as well as dynamic modeling of the extracellular matrix. It is covered by one of the thickest basement membranes in the body, and contains some of the longest polarized epithelia. We are currently studying the outcome of FAK disruption (and other kinases) during lens development and whether this has an impact on overall eye size. Electroporation of fluorescent signaling constructs into the intact lens also provide a means to uncover basic mechanisms of how epithelial cells impact membrane organization, and how this organization in turn impacts cellular behavior and morphology. This research may provide insight into the ophthalmological defects seen in children with congenital muscular dystrophy.
Laura Camms, Postdoctoral Fellow
Beth Grande, Administrative Assistant
Sarah Moseley, Postdoctoral Fellow
Bradley Pawlikowski, Postoctoral Scholar
Jordan Wolfe, Technician
Hui Zhang, Imaging Specialist
Beggs HE, Schahin-Reed D, Zang K, Goebbels S, Nave KA, Gorski J, Jones KR, Sretavan D, Reichardt LF: FAK deficiency in Cells Contributing to the Basement Membrane Results in Cortical Abnormalities Resembling Congenital Muscular Dystrophies. Neuron, 2003: 40(3) 501-514.
Liu G*, Beggs HE*, Park H.-T, Tang H, Xiong W.-C, Reichardt LF, Wu J, Rao Y: Netrin requires focal adhesion kinase and Src family kinases for axon outgrowth and attraction.. Nature Neuroscience, 2004: 7(11) 1222-1232.
Rico B, Beggs HE, Schahin-Reed D, Kimes N, Schmidt A, Reichardt LF: Control of Axonal Branching and Synapse Formation by Focal Adhesion Kinase. Nature Neuroscience 2004: 7(10): 1059-1069.
Tilghman, R.W., Slack-Davis, J.K., Sergina, N., Martin, K.H., Iwanicki, M., Hershey, D., Beggs, H.E, Reichardt, L. and Parsons, J.T. (2005) Focal Adhesion Kinase is required for the spatial organization of the leading edge in migrating cells. J. Cell Science. 118: 2613-23.
Essayem S, Kovacic-Milivojevic B, Baumbusch C, McDonagh S, Dolganov G, Howerton K, Larocque N, Ramiriz A, Ramos DM, Fisher SJ, Jorcano JL, Beggs H, Reichardt, LF, Ilic, D (2006) Hair cycle and wound healing in mice with a keratinocyte-restricted deletion of FAK. Oncogene. 25:1081-9
Braren R, Hu H, Beggs HE, Reichardt LF, Wang R: Cre-Mediated Deletion of fak in the Circulatory System Disrupts Vascular Remodeling. (2006) J. Cell Biology 172: 151-162.
DiMichele LA, Doherty J, Rojas M, Beggs HE, Reichardt LF, Mack CP, Taylor JM (2006) FAK is required for pathological hypertrophic cardiac remodeling but not for maintaining physiological heart function. (Accepted, Circulation Research)
Sundberg LJ, Thompson R, Beggs HE, Reichardt LF, Mack CP, Taylor JP. (2006) Inactivation of Focal Adhesion Kinase promotes smooth muscle cell differentiation. (JBC).
Shober, M., Raghavan, S., Nikolova, M., Polak, L., Pasolli, A., Beggs, H., Reichardt L.F. and Fuchs E. (2006) Defining roles for focal adhesion kinase in actin dynamics and focal adhesion turnover. (Submitted)
Hakim, ZS, DiMichele LA, Doherty JT, Homeister JW, Beggs HE, Reichardt LF, Schwartz RJ, Mack CP, Taylor JP (2006) Embryonic myocyte-restricted deletion of focal adhesion kinase leads to septal defects and perinatal lethality. (Submitted).
Beggs, H.E. (2006) Retinal Lamination and Integrity of the Lens Capsule Basement Membrane Require Focal Adhesion Kinase Signaling. (Manuscript in Preparation).
Hilary Beggs, Ph.D.
Beckman Vision Center
10 Koret Way
University of California, San Francisco
K127 (office), K130 (lab)
Beckman Vision Center
10 Koret Way, CB 0730
University of California, San Francisco
San Francisco, CA 94143-0730
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