The longfin inshore squid has long been an important organism in neuroscience research thanks to its giant axon—a nerve fiber that carries signals thr

National Geographic: Untangling mysteries of the brain—with the remarkable biology of squid

UNITED STATES
Thursday, July 29, 2021, 01:30 (GMT + 9)

The following is an excerpt from an article published by the National Geographic:  

Squid's giant nerve fibers have been essential to research for decades. Now breakthroughs in editing squid genomes could lead to a more complete understanding of nervous systems in general.

“We’ve got tuuuuuubes!” fisherman Matt Rissell shouts as he leans over the gunwale of the Skipjack to check his line. After a salty April morning spent bobbing off the coast of Cape Cod, Massachusetts, the first squid of the season are coming in.

Rissell reels and a foot-long male Doryteuthis pealeii (though everyone on this boat refers to it by its older name Loligo) emerges from the waves spouting water and waggling its two tentacles and eight sucker-covered arms. The iridescent skin of its mantle—the “tube”—is flecked with pink, teal, and gold, until in a flash, as Rissell brings the squid over the side, it transforms to an angry maroon.

Image: NOAA -->

Other boats are out for the squid run, too. Poles bend across the small fleet of reel-and-rod outfits gathered here in shallow waters where the squid come to spawn each spring. The animals spend the rest of the year jetting around deep underwater canyons, ensnaring fish, crustaceans, and even fellow squid. Further out, commercial trawlers drag long nets, each year landing thousands of tons of squid, most of which are destined for the deep fat fryer.

The squid pulled into the Skipjack, however, have a more cerebral purpose. They will be taken to the Woods Hole Marine Biological Laboratory a few miles to the west, where for nearly a century, these squid have played a vital role in neuroscience research. The animals have helped scientists shed light on everything from the basics of nerve signaling to the evolution of complex brains. Study of the squid’s unique biology could eventually lead to improved therapies for neurological and genetic disorders in humans.

Last year, this research took a major step forward when a group of scientists at the laboratory successfully used the gene editing tool CRISPR-Cas9 to disable, or “knock out,” a gene in the Doryteuthis squid—a first for any member of the talented group of mollusks known as cephalopods. The work paves the way for scientists to investigate the genetics behind cephalopods’ near extraterrestrial abilities, from squid’s color-changing skin cells to cuttlefish’s duplicitous mating behavior to octopus’s capacity for memory and learning.

“How have they figured out different ways to make these complex behaviors?” wonders molecular biologist Josh Rosenthal as he reels a squid into the Skipjack, then flips it off his jig into a tank of water where it disappears in a bloom of black ink. “These things that basically came more from a clam than from a vertebrate.”

Historically, however, it was another feature of the squid that made them famous among neuroscientists. As the Skipjack heads back with at least 70 squid in the tank, Rosenthal, who led the CRISPR research at the Marine Biological Laboratory, yells over the engine: “It was their giant nerve cells!”

Big squid axons

A few hours later, I see what Rosenthal means as Pablo Miranda Fernandez, a neuroscientist from the National Institutes of Health, takes one of the squid from the Skipjack up to his dissection room and without ceremony lops off its head. He immediately goes to work at a table covered with cold seawater, slicing open the squid’s translucent body and gingerly removing its viscera with metal forceps. He peels back the squid’s hard inner shell, or “pen,” to reveal a pair of nerve fibers, called axons, extending from the severed end of the squid into its well-muscled mantle.

“Pretty good,” he says, measuring the width of the fiber, which is about a fourth as thick as a cooked strand of spaghetti. Tying off the ends of the axon, Fernandez plops it in a dish of calcium-free water, so as not to disrupt the ions inside, which enable the nerve to fire. Hundreds of times larger than the largest axon in humans, its girth allows electrical impulses to travel rapidly into the mantle, so the squid can quickly jet away from danger.

Longfin inshore squid (Doryteuthis pealeii) hatchlings. On the left is a control hatchling; note the black and reddish brown chromatophores evenly placed across its mantle, head and tentacles. In contrast, the embryo on the right was injected with CRISPR-Cas9 targeting a pigmentation gene (Tryptophan 2,3 Dioxygenase) before the first cell division ; it has very few pigmented chromatophores and light pink to red eyes. Credit: Karen Crawford -->

Following the discovery of these giant fibers in 1936 (scientists initially thought they were blood vessels), researchers began using them for experiments on the chemical and electrical mechanisms of the nervous system and the brain. The squid axon was so big that scientists could attach electrodes to it and zap it, measuring changes in voltage. They could squeeze out the axoplasmic goo inside and study what it was made of. (continues...)

Author: James Dinneen / National Geographic | Read the full article by clicking de link here

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