Sharks Form Fins Like Other Vertebrates Do

By studying the catshark embryo, scientists in Japan showed that cartilaginous fish develop limbs and muscles in the same way as bony fish and land vertebrates.

AsianScientist (Oct. 13, 2017) – Scientists have discovered that cartilaginous fish such as sharks grow limbs in the same way as bony fish and land vertebrates. Their findings are published in the journal Nature Ecology & Evolution.

The development of limb muscle has been well studied in most land dwelling vertebrates such as rodent research models and humans. In these species, muscle precursors, or cells that will form limb muscle, travel to the limb bud of the embryo. These cells then multiply and form muscle tissue under the control of genes such as Lbx1 that coordinate limb-muscle formation. It is thought that this mechanism of development is shared with bony fish but not with cartilaginous fish.

In this study, a group of researchers led by Associate Professor Mikiko Tanaka at Tokyo Tech overturned earlier assumptions by studying catshark embryos as their research model. They demonstrate that Lbx1-positive cells are also found in cartilaginous fish fins and in hypobranchial (pertaining to the segment below the gills) muscles. In addition to Lbx1, the scientists found other genes that are involved in fin muscle formation in cartilaginous fish, including Pax3 and Myod.

Their results indicate that fin and muscle formation in cartilaginous fish occur via the same mechanism as that in bony fish and land dwelling vertebrates.

Tanaka pointed out that even though this is a new finding in the context of evolutionary development of land-dwelling vertebrates and fish, further studies are needed to address the details of developmental systems of migratory muscle precursor cells in limb and hypobranchial muscle formation. Additional investigations of older fish species and other key molecules regulating muscle development are also necessary.

The article can be found at: Okamoto et al. (2017) Migratory Appendicular Muscles Precursor Cells in the Common Ancestor to All Vertebrates.


Source: Tokyo Institute of Technology; Photo: James Hanlon/Flickr/CC.
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