"Bioelectric" effects illustrate the boundary that differentiates living and inert domains

As Vernadsky hypothesized there exists a qualitative hierarchy in the universe which distinguishes biological life from "dead" matter. Here is one more remarkable feature of living substance: its distinct and startling bioelectric property:


Transmembrane voltage potential controls embryonic eye patterning in Xenopus laevis

1. Vaibhav P. Pai, 
2. Sherry Aw, 
3. Tal Shomrat, 
4. Joan M. Lemire and 
5. Michael Levin*

1. ↵*Author for correspondence: michael.levin@tufts.edu

Summary

Uncovering the molecular mechanisms of eye development is crucial for understanding the embryonic morphogenesis of complex structures, as well as for the establishment of novel biomedical approaches to address birth defects and injuries of the visual system. Here, we characterize change in transmembrane voltage potential (V_mem) as a novel biophysical signal for eye induction in Xenopus laevis. During normal embryogenesis, a striking hyperpolarization demarcates a specific cluster of cells in the anterior neural field. Depolarizing the dorsal lineages in which these cells reside results in malformed eyes. Manipulating V_mem of non-eye cells induces well-formed ectopic eyes that are morphologically and histologically similar to endogenous eyes. Remarkably, such ectopic eyes can be induced far outside the anterior neural field. A Ca²⁺ channel-dependent pathway transduces the V_mem signal and regulates patterning of eye field transcription factors. These data reveal a new, instructive role for membrane voltage during embryogenesis and demonstrate that V_mem is a crucial upstream signal in eye development. Learning to control bioelectric initiators of organogenesis offers significant insight into birth defects that affect the eye and might have significant implications for regenerative approaches to ocular diseases.

Changing the bioelectric voltage in embryonic frog cell in tadpole's back caused cell to develop into a functioning eye. Credit: Michael Levin and Sherry Aw

For the first time, scientists have altered natural bioelectrical communication among cells to directly specify the type of new organ to be created at a particular location within a vertebrate organism. Using genetic manipulation of membrane voltage in Xenopus (frog) embryos, biologists at Tufts University's School of Arts and Sciences were able to cause tadpoles to grow eyes outside of the head area.