Platelets Pull Together

When a blood vessel is injured, platelets (green) – tiny blood cells without nuclei – are the first on the scene, sticking to the vessel walls surrounding the injury site and assembling a meshwork of fibrin molecules (red) between them. This platelet and fibrin bundle (or clot) then contracts, as shown in the video, which serves two purposes: closing the wound to prevent blood loss, and preventing the vessel itself from becoming blocked by the clot. Although scientists were aware of the major molecular players controlling this remarkable feat of compression, the precise mechanism at work was a mystery. Now state-of-the-art microscopy has uncovered the dynamics of clot contraction, revealing that platelets extend thin, arm-like projections, called filopodia (visible in the video), that grab and pull on the fibrin cables and draw the cells together.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Video by John Weisel, PhD, Perelman School of Medicine, University of Pennsylvania
• Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
• Video/image copyright held by the original authors
• Research published in Nature Communications, November 2017