WEBVTT - What Can We Learn from Fish about Walking?

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<v Speaker 1>Welcome to brain Stuff from how stuff works. Hey, brain stuff,

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<v Speaker 1>Lauren Vogel bomb here, where did you get that walk?

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<v Speaker 1>Like many people, you might guess our vertebrate gate originates

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<v Speaker 1>with the first backboned creatures to scramble out of the sea,

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<v Speaker 1>but a study published in the journal cell In indicates

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<v Speaker 1>that the first walkers did it underwater. The Late Devonian

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<v Speaker 1>vertebrate land invasion roughly three two million years ago was

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<v Speaker 1>a big deal in Earth's history. Previously confined to the ocean,

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<v Speaker 1>our tetrapod forefathers took to the surface world and over

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<v Speaker 1>the course of millions of years, traded fins and gills

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<v Speaker 1>for limbs and lungs. A tetrapod, by the way, just

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<v Speaker 1>means vertebrates with two pairs of limbs. The remarkable thing,

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<v Speaker 1>says the team of researchers, is that the neural circuits

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<v Speaker 1>involved an ambulatory limb control were already established millions of

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<v Speaker 1>years before the first tetrapod strutted its stuff. In other words,

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<v Speaker 1>much of the software was in place well before the

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<v Speaker 1>walk about hard wear. The researchers studied the neural circuitry

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<v Speaker 1>of the little skate, This cartilaginous fish might not be

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<v Speaker 1>much to look at, but it's considered one of the

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<v Speaker 1>most primitive vertebrates alive today. Travel back roughly four d

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<v Speaker 1>and twenty million years and you'll find a common ancestor

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<v Speaker 1>of both skates and tetrapods. The little skate is also

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<v Speaker 1>interesting because it's one of several ambulatory fish that walk

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<v Speaker 1>across the sea floor. The skate uses its large pectoral

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<v Speaker 1>fins to swim and smaller pelvic fins to walk with

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<v Speaker 1>alternating left right motions, much like the gate of a

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<v Speaker 1>land animal. This similarity impressed the researchers, but these similarities

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<v Speaker 1>would go beyond movement. The team employed RNA sequencing to

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<v Speaker 1>study the expressed genes in these skates motor neurons. Many

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<v Speaker 1>of these genes pop up in mammals as well, and

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<v Speaker 1>that includes neural subtypes involved in the muscle control of

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<v Speaker 1>bending and straightening limbs. This, according to the study findings,

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<v Speaker 1>constitutes a conserved genetic program for walking. Study co author

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<v Speaker 1>Jeremy S. Dayson says that neither swimming nor walking accurately

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<v Speaker 1>describe the skates movements, but perhaps this isn't too surprising

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<v Speaker 1>given the human centric nature of our language. He said,

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<v Speaker 1>via email. The skate ray mode I would call ambulatory swimming,

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<v Speaker 1>whereas the axial tail based is more like spinal swimming.

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<v Speaker 1>The ambulatory swimming mode is really the one which made

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<v Speaker 1>walking possible in both skates and tetrapods. The study sheds

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<v Speaker 1>light on the underwater history of walking, but the researchers

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<v Speaker 1>hope that it will lead to an improved understanding of

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<v Speaker 1>motor neurons and even the treatment of human neurological disorders.

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<v Speaker 1>Jason stresses that while the neural complexity of higher organisms

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<v Speaker 1>does hinder our study of animals such as mice, the

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<v Speaker 1>little skates archaic simplicity makes it a perfect starting point.

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<v Speaker 1>He said, I think one of the advantages of studying

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<v Speaker 1>neural circuits and skates is that they can accomplish this

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<v Speaker 1>behavior using a relatively simple set of connections between neurons

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<v Speaker 1>and muscle. We hope we can exploit the simplicity to

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<v Speaker 1>understand the basic architecture of the circuits controlling walking. The

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<v Speaker 1>exact wiring of these circuits is still not fully understood

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<v Speaker 1>in humans or other tetrapods, but such knowledge could one

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<v Speaker 1>day aid in the treatment and repair of human spinal

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<v Speaker 1>cord injuries. And motor neuron diseases such as amyotrophic lateral

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<v Speaker 1>sclerosis or a LS. But as the saying goes, you

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<v Speaker 1>have to crawl before you can walk or should we say, swim.

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<v Speaker 1>Today's episode was written by Robert Lamb and produced by

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<v Speaker 1>Tristan McNeil. For more on this and lots of other

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<v Speaker 1>topics on the go, visit our home planet, how Stuff

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<v Speaker 1>Works dot com