The development of the nervous system requires the proper differentiation, migration and morphogenesis of neurons. The morphogenesis of individual neurons and the assembly of the trillions of neuronal circuits that define the human nervous system occur through guided extension of axons and dendrites. The objective of this research is to better understand the calcium channels and downstream effector mechanisms that are responsible for the proper wiring of the brain. For this we must understand how nerve growth cones detect, integrate and respond to soluble, as well as cell- and substratum- associated guidance molecules in their environment. Mutations in genes involved in the detection and transduction of axon guidance information into directed neurite outgrowth are responsible for many deficits in cognitive function, including autisms, dyslexias, psychological disorders and mental retardations. Environmental factors that guide axons often stimulate intracellular calcium changes within growth cones. Interestingly, both growth promoting and inhibiting axon guidance cues have been shown to require intracellular calcium fluctuations. It is unclear how this simple ion can mediate distinct and even opposite effects on growth cone behavior, but many studies suggest that the frequency, amplitude and distribution of local calcium signals within growth cones determine the downstream effector mechanisms activated. Recent evidence suggests that the specific channel types involved in calcium influx or release from stores determines the effect on growth cone motility. This proposal will test the role of distinct transient receptor potential (TRP) channels on growth cone physiology and motility. TRP channels are plasma membrane cation channels composed of four subunits that are activated by diverse chemical and mechanical stimuli.
Aim 1 uses gain- and loss-of-function approaches to determine which subunits form mechanically gated channels by testing how these channels control axon outgrowth and guidance. As our preliminary data shows calpain activity is tightly regulated by mechanically induced calcium influx.
In Aim 2 we will investigate the molecular substrates of calpain proteolysis important for adhesion turnover and axon guidance. A better understanding of the molecular mechanisms through which calcium exerts such varied effects on growth cone motility will support treatment strategies for developmental disorders and neuronal injuries.

Public Health Relevance

The development and regeneration of a functional nervous system requires accurate guidance of axons and dendrites to their target locations and the subsequent assembly of proper synaptic connections. This proposal is focused on understanding the roles of mechanosensitive TRP channels on the regulation of axon outgrowth and guidance. As a number of cognitive disorders result from improper axon pathfinding, understanding the molecular basis for normal neural development is essential for designing therapeutic interventions.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1-F03A-N (20))
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Riddle, Robert D
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University of Wisconsin Madison
Schools of Medicine
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Kerstein, Patrick C; Patel, Kevin M; Gomez, Timothy M (2017) Calpain-Mediated Proteolysis of Talin and FAK Regulates Adhesion Dynamics Necessary for Axon Guidance. J Neurosci 37:1568-1580
Kerstein, Patrick C; Nichol IV, Robert H; Gomez, Timothy M (2015) Mechanochemical regulation of growth cone motility. Front Cell Neurosci 9:244
Kerstein, Patrick C; Jacques-Fricke, Bridget T; Rengifo, Juliana et al. (2013) Mechanosensitive TRPC1 channels promote calpain proteolysis of talin to regulate spinal axon outgrowth. J Neurosci 33:273-85