Harnessing Maxwell’s demon: A new view of axon growth based on the stochastic dynamics of actin networks

The mechanism of axon growth and guidance is a core, unsolved problem in neuroscience and cell biology. For nearly three decades, our view of this process has largely been based on deterministic models of motility derived from studies of neurons cultured in vitro on rigid substrates. Here I will suggest a fundamentally different, inherently probabilistic model of axon growth, one that is grounded in the stochastic dynamics of actin networks. This perspective is motivated and supported by a synthesis of results from live imaging of a specific axon growing in its native tissue in vivo, together with single-molecule computational simulations of actin dynamics. In particular, I will show how axon growth arises from a small spatial bias in the intrinsic fluctuations of the axonal actin cytoskeleton, one that produces net translocation of the axonal actin network by differentially modulating local probabilities of network expansion vs compaction. I will discuss the relationship between this model and current views of axon growth and guidance mechanism, and demonstrate how it offers explanations for various longstanding puzzles in this field. I will further discuss potential sources of the spatial inhomogeneity that allows stochastic fluctuation to produce directed motion.

Dr. Edward Giniger is a Senior Investigator at NIH National Institute of Neurological Disorders and Stroke (NINDS).

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