Meeting Abstract
The retino-tectal projection of lower vertebrates is an experimentally amenable neuronal circuit for studying mechanisms of axon pathfinding in situ. To establish the retino-tectal projection, optic axons must navigate through the optic tract to their target tissue in the midbrain- the optic tectum. Here, we studied how two essential cyto-mechanical factors -beta-catenin and Myosin II – function to regulate optic axon pathfinding and growth cone filopodia in the optic tract of whole brains taken from Xenopus tadpoles. We expressed a mutant of β-catenin that contains the alpha-catenin but lacks the Cadherin binding site (b-catNTERM) in, and applied the Myosin II small molecule inhibitor Blebbistatin to, optic axons in the optic tract of intact brains. Expression of β-catNTERM increased dispersion of optic axons in the dorsal half of the optic tract. In contrast, application of Blebbistatin inhibited extension of optic axons through the optic tract of whole brains. In addition, optic axons that expressed -catNTERM formed growth cones that were bulbous lacked filopodial protrusions, whereas growth cones of optic axons that were exposed to Blebbistatin displayed long, thin filopodial protrusions in situ. These results suggest that β-catenin and Myosin II differentially sculpt optic axonal projections and growth cone filopodial protrusions in the optic tract. More broadly, our findings imply that optic axons may express distinct types of growth cone filopodia that regulate specific axon pathfinding behaviors such as fasciculation and extension in the optic tract.
