Breaking symmetry - cell polarity signaling pathways in growth cone guidance and synapse formation.

Directional and positional information is essential for the diverse neuronal morphology and connectivity during development. The direction of axon growth is critical for building the correct networks among neurons, sometimes from far away. Neuronal synapses are asymmetric cell-cell junctions with distinct presynaptic and postsynaptic structures to convey neural activity in a directional fashion. Recent studies show that some of the key asymmetry is mediated by highly conversed cell polarity signaling pathways. These pathways, planar cell polarity and apical-basal polarity, are not required for the global axon-dendrite polarity. Therefore, the apparent distinct types of morphological asymmetry in the nervous system, growth cone turning and synaptic junctions, are mediated by similar cell polarity signaling mechanisms widely used in cellular and tissue morphogenesis.