fTracker: Semi-automated quantification of filopodial dynamics

Cellular motility underlies critical physiological processes including embryogenesis, metastasis and wound healing. During development, neurons undergo cellular migration and also extend processes for long distances through a complex microenvironment to appropriately wire the nervous system. The growth cone is a highly dynamic structure that responds to extracellular cues by extending and retracting filopodia and lamellipodia to explore the microenvironment and to dictate the path and speed of process extension. Neuronal responses to a myriad of guidance cues have been studied biochemically, however, these approaches fail to capture critical spatio-temporal elements of growth cone dynamics. Live imaging of growth cones in culture has emerged as a powerful tool to study growth cone responses to guidance cues but the dynamic nature of the growth cone requires careful quantitative analysis. Space-time kymographs have been developed as a tool to quantify lamellipodia dynamics in a semi-automated fashion but no such tools exist to analyze filopodial dynamics.

We present an algorithm to quantify filopodial dynamics from cultured neurons imaged by time-lapse fluorescence microscopy. The method is based on locating the end tips of filopodia and tracking their locations as if they were free-moving particles. Analysis of test data sets reveals that the algorithm reliably reproduces velocity measurements determined through manual tracing of individual filopodia through consecutive frames but greatly reduces the time involved. The algorithm is a useful tool and should be broadly applicable to filopodial tracking from multiple cell types.

For a complete description and analysis of the fTracker algorithm, please
refer to the article in the Journal of Neuroscience Methods.

Depiction of different ways fTracker can measure filopodial dynamics:

fTracker (zip file containing all the components)
fTracker Manual