Voltage-gated sodium channel activity mediates sea urchin larval skeletal patterning through spatial regulation of Wnt5 expression

Defining pattern formation mechanisms during embryonic development is important for understanding the etiology of birth defects and to inform tissue engineering approaches. In this study, we used tricaine, a voltage-gated sodium channel (VGSC) inhibitor, to show that VGSC activity is required for normal skeletal patterning in Lytechinus variegatus sea urchin larvae. We demonstrate that tricaine-mediated patterning defects are rescued by an anesthetic-insensitive version of the VGSC LvScn5a. This channel is expressed in the posterior ventrolateral ectoderm where it spatially overlaps with Wnt5. We show that VGSC activity is required to spatially restrict Wnt5 expression to this ectodermal region that is adjacent and instructive to clusters of primary mesenchymal cells (PMCs) where secretion of the larval skeleton is initiated as triradiates. Tricaine-mediated Wnt5 spatial expansion correlates with the formation of ectopic PMC clusters and triradiates. These tricaine-mediated defects are rescued by Wnt5 knock down, indicating that the spatial expansion Wnt5 is responsible for the patterning defects induced by VGSC inhibition. These results demonstrate a novel connection between bioelectrical status and the spatial control of patterning cue expression during embryonic pattern formation. Summary statement Inhibition of voltage-gated sodium channels perturbs Wnt5-mediated patterning of the sea urchin larval skeleton.