ISM 2022 (Microscopy)

FRACTAL DIMENSION AND FRACTIONAL CONCAVITY IN GROWTH CONES OF OPTIC AXONS IN XENOPUS LAEVIS WHOLE BRAINS

Tamira Elul Valerie Lew Sukaynah Khetani
College of Osteopathic Medicine, Basic Sciences, Touro University California, Vallejo, CA, USA

Proper embryonic development of neuronal circuits requires that axons navigate specific paths towards their specific targets in the brain. Growth cones at the tips of axons both generate force for and guide the axons along their paths in the embryo. Quantitative analysis of growth cone morphology provides data relevant for deciphering growth cone motility behaviors. In particular, growth cone morphology, physical projections (filopodia and lamellipodia), shape, and dimension can influence overall motility. Previous studies have only used basic scoring methods, such as measuring area, length, width and number of protrusions, to analyze growth cones, which may not accurately describe the complexity of growth cone morphology. Here, we applied two novel shape measures to growth cone contours of optic axons from Xenopus laevis tadpoles in situ. We calculated fractal dimension and fractional concavity- which measure rate of scaling of detail and relative concavity of the border contour, respectively, to growth cones of optic axons in whole brains. We applied these measures to determine differences between GFP expressing control and experimental growth cones treated with the Myosin II inhibitor, Blebbistatin. Surprisingly, only fractional concavity was able to distinguish between control and Myosin II inhibited growth cones whereas fractal dimension did not reveal differences between the control and Blebbistatin exposed growth cones. This study advances our understanding of quantative methods for assessing complexity of growth cone contours, a proxy for growth cone motility that drives formation of neuronal circuits during development of the nervous system.