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Hemoglobins in Different Species Evolved from Same Ancestral Gene, New Study Suggests

Thanks to the marine worm Platynereis dumerilii (image), an animal whose genes have evolved very slowly, scientists from the French National Centre for Scientific Research (CNRS), Université de Paris, and Sorbonne Université, in association with others at the University of Saint Petersburg and the University of Rio de Janeiro, have shown that while hemoglobin appeared independently in several species, it actually descends from a single gene transmitted to all by their last common ancestor. These findings were published online on December 29, 2020 in BMC Evolutionary Biology. The open-access article is titled “Globins in the Marine Annelid Platynereis dumerilii Shed New Light on Hemoglobin Evolution in Bilaterians.” Having red blood is not peculiar to humans or mammals. This color comes from hemoglobin, a complex protein specialized in transporting the oxygen found in the circulatory system of vertebrates, but also in annelids (a worm family whose most famous members are earthworms), molluscs (especially pond snails), and crustaceans (such as daphnia or “water fleas”). It was thought that for hemoglobin to have appeared in such diverse species, it must have been “invented” several times during evolution. But recent research has shown that all of these hemoglobins, thought to have been born “independently,” actually derive from a single ancestral gene. Researchers from the Institut Jacques Monod (CNRS/Université de Paris), the Laboratoire Matière et Systèmes Complexes (CNRS/Université de Paris), the Station Biologique de Roscoff (CNRS/Sorbonne Université), the Universities of Saint Petersburg (Russia) and Rio de Janeiro (Brazil), conducted this research on Platynereis dumerilii, a small marine worm with red blood.

This worm is considered to be an animal that evolved slowly, because its genetic characteristics are close to those of the marine ancestor of most animals, Urbilateria (Urbilateria is the last common ancestor of bilaterians, i.e., animals with bilateral (left-right) symmetry and complex organs, apart from species with simpler organization such as sponges and jellyfish). Studying these worms by comparing them with other species with red blood has helped in tracing back to the origins of hemoglobins.

The research focused on the broad family to which hemoglobins belong: globins, proteins present in almost all living beings that “store” gases like oxygen and nitric oxide. But most globins usually act inside the cells because they do not circulate in the blood as hemoglobin does.

The current work shows that in all species with red blood, it is the same gene that makes a globin called “cytoglobin” that independently evolved to become a hemoglobin-encoding gene. This new circulating molecule made oxygen transport more efficient in their ancestors, which became larger and more active.

Scientists now want to change scale and continue this work by studying when and how the different specialized cells of bilaterian vascular systems emerged.


The Platynereis dumerilii vascular system in three segments. (Credit: © Song et al. / BMC Evolutionary Biology).

[News release] [BMC Evolutionary Biology article]