Cell MotilityHow do cells assemble, organize their shape, move, and target molecules to specific intracellular locations? Motility is essential for nearly all cell processes.
Research on cellular motility is centered at The Pennsylvania Muscle Institute (PMI) , an interdisciplinary group of research investigators focused on understanding the mechanisms and regulation of motile biological systems. Research is conducted using biophysics, biochemistry, genetics, physiology and ultrastructure to understand cell migration, intracellular transport, smooth, cardiac and skeletal muscle contraction, the structure/function relationship of molecular motors, chromosome segregation, cell division, muscle cell development, myofibril assembly and gene therapy targeted to muscle. The PMI is prominent in technological and methodological development for these investigations especially in advanced light microscopy, structural spectroscopy, photochemical reagents, image processing, and molecular biology. Motility research and graduate and post-doctoral research opportunities span the following areas:
Cell migration includes whole-cell locomotion and the regulation of the cell shape and extracellular attachment. Cell migration is crucial for several normal and pathological processes, including: cell and tissue development, wound healing, immune response, and metastases of tumors.
Intracellular transport is the movement and targeting of vesicles and proteins to specific cellular regions. Sometimes this transport occurs over long distances, like down the nerve axon, and sometimes this transport is simply the movement of a vesicle through the cell cortex. Transport also includes the proper delivery and localization of organelles (e.g., mitochondria).
Members of the Pennsylvania Muscle Institute are using and developing state-of-the-art techniques to understand the molecular events required for the regulation of cell migration and intracellular transport.
As with non-muscle motility, the general paradigm cells use for generating motion is a motor protein sliding along a linear filamentous track. This architecture was first discovered in muscle cells because these elegant machines express and assemble concentrated and highly periodic interdigitating arrays of myosin and actin filaments that are particularly amenable to structural, mechanical and biochemical studies. The filaments do not change length when the muscle contracts, but they slide relative to each other using energy liberated by hydrolysis of ATP to ADP and phosphate. The relationships between the biochemical steps of ATP hydrolysis, the mechanical development of force and filament sliding and the molecular structural changes are the major goals of this research.
State-of-the-art technologies, such as laser photolysis of 'caged' substrates and signaling molecules, time-resolved electron microscopy, optical traps (laser tweezers), fluorescence polarization spectroscopy and molecular genetics are applied to discover the mechanism of chemical-to-mechanical energy conversion.
Control of muscle contraction takes many forms, including calcium signaling, phosphorylation by specific kinases and receptor-effector signal cascades. As with contraction, signaling and control of muscle cells act as prardigms for corresponding processes throughout cell biology. Modern biophysical and molecular biological techniques are being applied to detail the molecular mechanisms of these pathways. PMI laboratories are prominent in developing new techniques with broad impact.
PMI members are determining - at the atomic level - how molecular motors use ATP to generate motility. Members use a combination of techniques to determine the ATP-induced structural changes in the motor that lead to force generation. These techniques include single-molecule spectroscopy, single-molecule force measurements, heterologous expression of mutant molecular motors, and transient biochemical kinetic measurements.
In addition to the therapeutic applications of gene transfer, viral-mediated gene transfer is being used to understand properties of muscle contraction, adaptation, and energetics. By overexpressing both normal and mutant genes in adult muscle, one can perturb the conditions of muscle after development has taken place. These studies include the expression of 1) contractile proteins such as Troponin C, 2) growth factors such as IGF-I and myostatin, and 3) enzymes which can attenuate ischemic-reperfusion injury, such as catalase and arginine kinase.
Myofibrillogenesis, one of the major steps in the early development of skeletal and cardiac muscles, occurs in an orchestrated series of events involving the formation of actin and myosin filaments, their assembly into an interdigitating array and their interaction with cross-linking proteins to form the sarcomere. We still know very little about the roles played by individual sarcomeric proteins in the assembly of myofibrils. New techniques of molecular biology and genetics combined with advances in biophysical and imaging techniques provide tools for examining this problem that were not possible in the past.
This program is to use such a multidisciplinary approach combining the techniques of cell biology, biophysics, genetics and molecular biology to discover important steps in the differentiation of precursor cells into skeletal and cardiac muscle cells and the parameters governing the assembly of myofibrils.
A very recent area of research concentration is nanotechnology. The Institute’s involvement has been in development of techniques to manipulate and study single functioning protein molecules. In many enzyme and polynucleotide systems, important elementary events at the molecular level are obscured within the average behavior of a molecular population. Studying enzymes one at a time has only recently become technically feasible but new information, not otherwise available, can be gained from such an approach. Work in this area will allow, for the first time, measurements of time-resolved structural information, forces, elasticity and molecular displacements on single biomolecules.
The immediate interest in developing these new techniques is for investigating the molecular mechanisms underlying motor protein-based cell motility and muscle contraction. However these methods are applicable to all enzymes that undergo structural changes between compact domains during their functional activity. The PMI will serve as a resource center for single molecule nanotechnology studies of enzyme systems outside cell motility, welcoming other investigators to study their proteins of interest by these powerful methods.
For more information on the Pennsylvania Muscle Institute, and the investigators involved in the above programs, please visit http://www.med.upenn.edu/~pmi/
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