果冻影院

Published in the Journal of Cell Science, Professor John Martin (果冻影院 Division of Medicine) thinks a single genetic molecular event听(inheritable epigenetic change) in an egg-laying animal may have resulted in the first formation of blood platelets, approximately 220 million years ago.

In mammals and humans, platelets are responsible for blood clotting and wound healing, so play a significant role in our defence response. Unlike our other cells, they don鈥檛 have nuclei 鈥� so are unique to mammals, since other classes of animal such as reptiles and birds have blood clotting cells with nuclei.

Our platelets are formed from megakaryocytes that mature in the bone marrow. When these megakaryocytes are released into the blood stream and reach the very high-pressure blood vessels the lungs, they 鈥榖urst鈥� apart, each cell releasing thousands of platelets inside the bloodstream.

The researchers suggest that millions of years ago a mammalian ancestor 鈥� possibly an animal related to the duck-billed platypus - underwent the very first formation of platelets, thanks to a sudden genetic change in the nucleus of its blood clotting cells that meant normal cell division did not take place causing the cells to increase in size.

If so, those much larger cells might then have been forced to burst inside the first capillaries they met in the animal鈥檚 blood stream, releasing their cytoplasmic fragments. These fragments proved to be more efficient at stopping bleeding, so if this genetic change was inheritable, it would have given its offspring a major advantage through natural selection. An animal with this epigenetic change could stem bleeding from fighting or wounds much better than its competitors, and so live longer.听

Professor Martin, Professor of Cardiovascular Medicine at 果冻影院, says: 鈥淏ecause of the uniqueness of platelets, it is reasonable to suggest that a unique event led to their origin. This was a radical, internal evolution occurring in a single animal, on a single day, 220 million years ago, and was then reinforced by natural selection.鈥�

Professor Martin and his colleague Professor Paolo D鈥橝vino (University of Cambridge) then suggest that this single cellular rapid change ultimately听led to the development, over 120 million of years, to the placenta, allowing the foetus to be retained inside the mother for longer-term development and thus allowing evolution to achieve live birth. The ability to clot wounds is an essential element of live birth by means of a placenta, since the placenta splits from the mother鈥檚 uterus during the birth process. The female would not survive birth and therefore not be able to suckle her offspring if she were unable to stem the bleeding.听听

In their paper, Professors Martin and D鈥橝vino propose experiments that would support their hypothesis, including in vitro and in animal models.听

鈥淲ithout this single critical epigenetic change, we suggest mammals would never have evolved, and therefore human beings would not be around today鈥�, says Professor Martin. 鈥淲ith this research, we鈥檝e laid down a marker based on the available evidence 鈥� and we鈥檙e听 suggesting these experiments that will either support or help to refute our hypothesis.鈥�

Links

• 果冻影院 Division of Medicine

Image

• Platypus in a vintage book History of animals, by Shubert/Korn, 1880. Credit:

Media contact听

Henry Killworth

Tel: +44 (0) 7881 833274

E: h.killworth [at] ucl.ac.uk