Split-second of evolutionary cellular change could have led to mammals

A newly-published hypothesis, led by a UCL researcher, suggests a momentary leap in a single species on a single day millions of years ago might ultimately have led to the arrival of mammals - and therefore humans. Published in the Journal of Cell Science , Professor John Martin (UCL Division of Medicine) thinks a single genetic molecular event (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't have nuclei - 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 'burst' apart, each cell releasing thousands of platelets inside the bloodstream. The researchers suggest that millions of years ago a mammalian ancestor - 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.