The dorsal fin of fish originated the limbs of vertebrates

The dorsal fin of fish originated the limbs of vertebrates

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A team from the Andalusian Center for Development Biology –a joint center of the Higher Council for Scientific Research and the Pablo de Olavide University of Seville– has led a work that has identified the evolutionary origin of the limbs of vertebrates: the dorsal fin of the fish.

It is believed that this key evolutionary event happened about 400 million years ago. The finding, which is published in the magazine Nature Genetics, has been achieved through molecular and genetic evidence.

The study of the fossil record and of species such as coelacanths and rays, which are the oldest fish, had already shown that the limbs developed from modifications of the paired fins (pectoral and pelvic) of the fish, from which the human being is descended.

Thus, the arms and hands evolved from the pectoral fins while the legs and feet evolved from the pelvic fins. However, until now the evolutionary origin of these structures was unknown.

As explained José Luis Gómez-Skarmeta, co-director of the work, “Through functional assays in fish and mice and through the CRISPR technique, we have demonstrated the evolutionary conservation of the function of the Sonic hedgehog (Shh) gene in the limbs of all vertebrates”.

In addition, scientists have found the fundamental role of a part of DNA, the regulator element ZRS, both in the formation of the even fins and in the development of the dorsal fin.

«We have shown that this element is essential not only for the formation of the even fins of the fish but, surprisingly, for the formation of the dorsal fins. This indicates that the set of genes necessary to build a pectoral and a dorsal fin are the same and, therefore, have a common evolutionary origin.”, Says Juan Ramón Martínez Morales, the other director of the work.

Congenital malformations of the extremities

The study has revealed that in fish, unlike what happens in mice, removal of the ZRS element does not drastically affect the development of the paired limbs.

Thus we discovered the existence of another Shh regulatory element unknown until now, but conserved in humans, and that also activates the expression of Shh in the extremities.«, Says Joaquín Letelier, first author of the work.

«We found that when both Shh regulatory elements were eliminated using the CRISPR technique, the pectoral and pelvic fins, as well as the dorsal fin, disappeared.”, He adds.

This discovery opens new avenues of research in biomedicine, since mutations in the Shh gene cause polydactyly, a genetic disorder in which a vertebrate is born with more fingers or toes than its share. These mutations could also be the cause of other congenital limb malformations.

Via Sinc Agency

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