Molecular basis of cell shape and mechanics in the nervous system

Effect of calcium ions on NF packing. In the presence of millimolar calcium, neurofilament-rich gels condense dramatically. This, together with other data from cellular studies raises the possibility that divalent cation concentrations may facilitate intermediate remodeling in nerve cells (from Kumar and Hoh, 2004).

The question of how neurons and glial cells establish and maintain their shape is of tremendous fundamental and technological importance. Throughout their development, neuronal and glial morphology and mechanics influence proliferation, differentiation, synaptogenesis, and the transduction of electrical and biochemical signals; thus, understanding how these cells control their shape is central to understanding neurophysiology. Moreover, from a bioengineering perspective, the ability to controllably manipulate neuronal shape would be of limitless value in the design of neural tissue engineering systems and devices which require spatial patterning of neurons.

Cultured neuroblastoma cells stained for F-actin (green) and nuclear DNA (blue). These cells form elongated, actin- and intermediate filament-rich processes which transform into neurites when the cells differentiate in culture.

We seek to understand how the elements of the neuronal cytoskeleton, together with the cell's attachment to the extracellular matrix, physically organize and interact to produce shape stability. To accomplish this, we are taking a multidisciplinary approach that includes live-cell fluorescence imaging, atomic force microscopy, use of culture substrates of defined shape, size, and/or compliance, and traditional biochemical and cell biological methods. We have also recently helped to develop a method to focally disrupt cytoskeletal elements using femtosecond laser pulses, and we are beginning to use this to dissect mechanical contributions of individual cytoskeletal systems.

A schematic of axonal neurofilament assembly. Neurofilaments (NFs) are intermediate filaments that represent the most abundant cytoskeletal element in large, myelinated axons. NFs run in parallel along the axon and interact through electrosteric forces mediated by their unstructured sidearm domains (from Kumar et al., 2002).