Genome complexity in embryology: control by electricity (Introduction)

by David Turell , Friday, July 06, 2018, 19:20 (2333 days ago) @ David Turell

Bio-electric fields are shown to control embryological formations of tissues. The work is on brainless tadpoles:

https://www.quantamagazine.org/brainless-embryos-suggest-bioelectricity-guides-growth-2...

"In recent years, by working on tadpoles and other simple creatures, Levin’s laboratory has amassed evidence that the embryo is molded by bioelectrical signals, particularly ones that emanate from the young brain long before it is even a functional organ. Those results, if replicated in other organisms, may change our understanding of the roles of electrical phenomena and the nervous system in development, and perhaps more widely in biology.

“'Levin’s findings will shake some rigid orthodoxy in the field,” said Sui Huang, a molecular biologist at the Institute for Systems Biology. If Levin’s work holds up, Huang continued, “I think many developmental biologists will be stunned to see that the construction of the body plan is not due to local regulation of cells … but is centrally orchestrated by the brain.”

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"But it’s not just the brain that uses bioelectric signaling — the whole body does. All cell membranes have embedded ion channels, protein pores that act as pathways for charged molecules, or ions. Differences between the number of ions inside and outside a cell result in an electric gradient — the cell’s resting potential. Vary this potential by opening or blocking the ion channels, and you change the signals transmitted to, from and among the cells all around. Neurons do this as well, but even faster: To communicate among themselves, they use molecules called neurotransmitters that are released at synapses in response to voltage spikes, and they send ultra-rapid electrical pulses over long distances along their axons, encoding information in the pulses’ pattern, to control muscle activity.

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"In 2015, Levin, his postdoc Vaibhav Pai, and other collaborators showed experimentally that bioelectric signals from the body shape the development and patterning of the brain in its earliest stages. By changing the resting potential in the cells of tadpoles as far from the head as the gut, they appeared to disrupt the body’s “blueprint” for brain development. The resulting tadpoles’ brains were smaller or even nonexistent, and brain tissue grew where it shouldn’t.

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"Herrera-Rincon and the rest of the team didn’t stop there. They wanted to see whether they could “rescue” the developing body from these defects by using bioelectricity to mimic the effect of a brain. They decided to express a specific ion channel called HCN2, which acts differently in various cells but is sensitive to their resting potential.

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"To make embryos express it, the researchers injected messenger RNA for HCN2 into some frog egg cells just a couple of hours after they were fertilized. A day later they removed the embryos’ brains, and over the next few days, the cells of the embryo acquired novel electrical activity from the HCN2 in their membranes.

"The scientists found that this procedure rescued the brainless tadpoles from most of the usual defects. Because of the HCN2 it was as if the brain was still present, telling the body how to develop normally. It was amazing, Levin said, “to see how much rescue you can get just from very simple expression of this channel.” It was also, he added, the first clear evidence that the brain controls the development of the embryo via bioelectric cues.

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"Although Levin’s work is gaining recognition, the emphasis he puts on electricity in development is far from universally accepted. Epigenetics and bioelectricity are important, but so are other layers of biology, Zhao said. “They work together to produce the biology we see.” More evidence is needed to shift the paradigm, he added. “We saw some amazing and mind-blowing results in this bioelectricity field, but the fundamental mechanisms are yet to be fully understood. I do not think we are there yet.”

"But Nuccitelli says that for many biologists, Levin is on to something. For example, he said, Levin’s success in inducing the growth of misplaced eyes in tadpoles simply by altering the ion flux through the local tissues “is an amazing demonstration of the power of biophysics to control pattern formation.”

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"The passage of time and the efforts of others carrying on Levin’s work will help his cause, suggested David Stocum, a developmental biologist and dean emeritus at Indiana University-Purdue University Indianapolis. “In my view, his ideas will eventually be shown to be correct and generally accepted as an important part of the framework of developmental biology.'”

Comment: Developing a whole body from one fertilized cell is a stupendous job and obviously requires many mechanisms, and a designed process.