Fig. 2.

Bioelectrical control of cellular and tissue level processes in development. Overview of some pertinent developmental roles regulated by bioelectrical signals at different levels of organization. (A) Intercellular communication. (i) Transmission of state between cells can occur via long cellular processes termed nanotubes and cytonemes, e.g. between zebrafish melanocytes (M) and xanthophores (X). This process is dependent on potassium channel-mediated regulation of Vmem and gap junctions. (ii) Nanotubes and cytonemes also facilitate the transmission of small molecules and ions between cells. This process can require gap junctional complexes. (iii) Long-distance targeted signaling can also occur through regional release of growth factors (red dots) in a process that is dependent on potassium channel function. Blue and green indicate different character states of cells induced by differential electrical signaling. (B) Tissue-level regulation. The Drosophila imaginal disc epithelium is electrically coupled and bounded, causing localized coordination of developmental signals. A trans-epithelial potential (TEP) exists across the stratified epithelia. (C) Signaling within and across organ and structures. (i) In the organ of Corti of the inner ear, the differential expression of potassium channels and gap junctions across the structure supports the generation and maintenance of large electrical potential in the endolymph, providing an electrical gradient for signaling after hair cell activation. (ii) Early development of the vertebrate limb is marked by regional shifts in currents and the creation of electrical fields demarcating a limb field in early limb buds with specific limb-forming potential (blue). (D) Signaling among and across tissues comprising organismal-level regulation. Many organisms show local as well as global electrical fields. For example, planaria, hydra and Xenopus show variation of bioelectric fields across their anterior to posterior axes.