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quinta-feira, junho 24, 2010

From whence we came

By Tom Spears, The Ottawa Citizen June 24, 2010 2:14 PM

OTTAWA — Most days, Marie-Andrée Akimenko writes research papers with titles like "Inhibition of BMP signaling during zebrafish fin regeneration disrupts fin growth and scleroblasts differentiation and function."

Today she publishes something different, a modern Just So Story. The title isn't "How the Tetrapod Got its Legs," but it should be.

Akimenko is a University of Ottawa biologist who studies fish fins. Fins of zebrafish, specifically -- a minnow-sized, stripy fish which has the ability to re-grow severed body parts. She began this work some years back at the Ottawa Hospital Research Institute, looking for genetic clues that could help humans regenerate healthy tissue in injured arms or legs. Along the way, she turned her gaze back 360 million years, to the time when the first animals with legs appeared.

Today, geneticists have become our storytellers, our links with the invisible past. The zebrafish is Akimenko's time machine, its genes revealing glimpses into why all the creatures in the sea had fins at one stage, but not today.

This is a tough one to understand. How could a fish just grow legs? It mystifies us, and so this part of evolutionary theory is a common target for cheap attacks from creationists. Therefore, it's extremely valuable that a scientist has now found a way in which a genetic tweaking makes a zebrafish embryo stop growing fins, and start growing an appendage that looks like a leg. If she can tweak a gene in the lab, maybe one of the many mutations that pop up in nature could do the same.

A tetrapod is something with four legs and a spine. A frog, a dinosaur, a giraffe in the high veldt. There has been life on Earth for nearly four billion years, but tetrapods for only one-tenth of that.

Before tetrapods, however, there were lots of fish. So, what's the connection?

In the zebrafish, Akimenko found a new family of genes that seemed important to how fins develop in the embryo. These genes appear in different fish species, but have disappeared from animals with legs. The genes allow fish to produce a fibrous material in fins called actinotrichia. Here's where her detective work starts.

To learn what a gene does, one method is to add a chemical that temporarily stops it from working, and see what happens to the animal. Akimenko's team "knocked down" two of the four actinotrichia genes in a zebrafish embryo, and found that the fish appeared to stop growing fins.

Instead, it began growing features that look like the "buds" (or embryonic beginnings) of legs.

But this was a frustratingly short look into the past.

Read more here/Leia mais aqui: Ottawa Citizen