Fish covered in tooth-like armour could help reveal how teeth evolved

New Scientist, 2nd July 2021

Armoured catfish Pterygoplichthys species, photo by the US Geological Survey

A pet fish adorned with tooth-like scales is helping biologists tackle a longstanding debate about the origin of teeth, and explore how body structures can be lost and regained during evolution.

The suckermouth armoured catfish is commonly found in pet shops and, unusually for a bony fish, has tooth-like structures called odontodes covering its skin. These physically resemble teeth, erupting from thickened patches of skin to form layered structures of pulp, dentine and enamel, and similar genes appear to be active in both during development. But which evolved first, and how did tissues gain or regain them?

Their evolutionary history is complicated, because while ancient fish had similar structures, they were lost in most bony fish, but retained in fish with cartilage-based skeletons, like sharks. They re-emerged again independently in four different bony fish groups, including armoured catfish.

To find out more, biologists needed the ability to study and manipulate genes in a fish with skin odontodes, but zebrafish, a common model animal for these kinds of experiments, don’t have them.

Now Shunsuke Mori and Tetsuya Nakamura at Rutgers, the State University of New Jersey, have analysed gene activity in developing suckermouth armoured catfish skin odontodes. They uncovered a network of genes very similar to those found in developing teeth. “Most of the genes are shared,” says Nakamura.

One of these genes, pitx2, is needed for the first steps of tooth development, yet is absent from the skin odontodes of sharks. So Mori and Nakamura used gene silencing techniques to reduce the activity of pitx2 in the catfish and found that the odontodes didn’t develop properly…

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Mini-heart grown in the lab can pump fluid

New Scientist, 1 July 2021

Stem cells have been used to grow an embryonic-like “heart” that can pump fluid around a system of tiny channels on a laboratory slide.

The mini-heart could allow researchers to explore how physical forces, such as blood flow, shape the early stages of human heart development and give new insights into congenital heart defects.

Current efforts to grow human heart tissue involve coaxing human stem cells to form spheres of heart tissue, known as organoids, in a lab dish. While these offer invaluable insights, they don’t accurately mimic the shape of the heart, which, in the earliest stages of its development, looks like a simple, straight tube.

“If we really want to model organ function, we need to figure out how to make these things in the form of tubes,” says David Sachs at the Icahn School of Medicine at Mount Sinai.

Sachs and his colleagues seeded human stem cells, known as induced pluripotent stem cells, onto a plastic plate containing tiny wells connected by hair-thin channels. By applying different combinations of chemical signals to different areas of the plate, they were able to get the cells to form tubes made of human heart muscle.

The heart tubes pumped fluid around the channels, Sachs told the International Society for Stem Cell Research’s 2021 meeting, held virtually last week…

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