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Curious: Presentations by Young Researchers I

Are a salmon’s jaw and our ears the same? Three young Japanese researchers in Chicago made curious presentations about their studies at the Japan Information Center of the Consulate General of Japan at Chicago on April 13.
The researchers have formed the Japanese Researchers Crossing in Chicago to help each other and held meetings to share their studies. They also have invited people who are interested in learning new things.
This time, Noritaka Adachi, Postdoctoral Scholar ? Organismal Biology and Anatomy at the University of Chicago, spoke about “What is morphology?”; Tomoya Kubota, Postdoctoral Scholar ? Department of Biochemistry and Molecular Biology at the University of Chicago, spoke about “Bedside-to-Bench, and vice versa”; and Kentaro Asai, Doctoral Student ? Economics at the University of Chicago spoke about “Use of Big Data by Economists”.

What is morphology?

Morphology is the study of structures such as bones, muscles, and nerves, and observes and describes the positional relationship among them. Its history goes back more than 200 years, and Goethe named the study as “morphologie” in German.
Morphology is divided into two main fields. One is comparative morphology, and another is functional morphology. Adachi is in the field of comparative morphology.

Are a salmon’s jaw and our ears the same?

Mammals including humans have three bones in each ear. They are malleus, incus, and stapes. The three bones transmit the vibration from eardrum to nerves in an ear. Adachi has formed a hypothesis that the three bones in an ear and a salmon’s jaw are the same.

What is the evidence?
A salmon jaw has an upper jaw, lower jaw, and a bone, which upholds the upper jaw. A morphologist discovered that the three parts corresponded to the three bones in a human ear a long time ago.
Further study found that a muscle was attached to salmon’s jaw to chew food, and it had a trigeminal nerve to move the muscle. Besides, it has a semicircular canal above the bone. Adachi said that human ear had a similar positional relationship with a salmon’s jaw, and the muscle was extended to the ear and controlled by a trigeminal nerve. Humans also have a semicircular canal in the ear.

The second piece of evidence is that the three bones found both in humans and salmon are developed from the same part of an embryonic cell. A series of fossils also show the process by which bones of the jaw gradually became smaller and entered into the ear.

Other researchers questioned that if a salmon’s jaw had gotten into our ears, we would have only one ear because salmon had only one jaw. Adachi explained that mammals developed four to five bones, and one became a jaw while the others went into each ear.

How are fingers developed?

Adachi spoke about how hands and fingers were evolved from a fin. The primitive fish Eusthenopteron had bones in its fin while Acanthostega had arm bones and eight fingers. However, the evolution between the two was unknown until about 2000.

Adachi’s teacher went to Canada within the Arctic Circle and found fossils. They had fishlike scales and salamander or alligator-like heads. They had arms with bones and joints, and at the same time, they had fins. The fins were located under the body and had many places to attach to muscles, which might enable them to do push-ups. These facts indicate that the fish could have been moving on the land. They are named as Tiktaalik.

Did fish have genes to make fingers?

Adachi explained that the Hox gene plays an important role for making fingers. Mice, which have no Hox gene, cannot grow fingers.
Mice have a genomic area to control Hox gene expression, and fish also have it. When such an area of zebrafish was inserted into mice, no activity was observed. Therefore, it was believed that fish had no mechanism to produce fingers.
However, discovery of fingers in fish fins moved Adachi’s teacher to think that fish might have such a mechanism. He used a sturgeon, which had a more primitive character, and found that a sturgeon’s fin had Hox gene expression. Rays, which are more primitive than sturgeon, also had it. The primitive character may have been lost in zebrafish. After the findings, his teacher made a hypothesis that fish might have a part of a mechanism which would produce mouse’s fingers. Adachi said that this scientific article was one of the hot topics in Evo-Devo (Evolutionary developmental biology).

What does a human’s ancestry look like?

Humans looked like amphibians at a certain period, and looked like fish in another period. Going way back, fish were jawless vertebrates such as hagfish and lamprey. Lampreys don’t have a jaw, semicircular canal, pectoral fins, abdominal fins, shoulders, necks, and have only one nasal cavity.

Adachi said that he wanted to study how lamprey-like creatures developed a jaw, tow-nasal cavity, and fins. He said that lampreys and gnathostomes, fish with jaws, had different reactions when a protein sent out signals to produce jaws. Their areas of receptors are different, and the difference may relate to formation of jaws. He also formed a hypothesis about how fins were evolved and has continued to study it.
Other presentations will be continued in the next issue.