A fibripositor deposits a collagen fiber into the extracellular space.
Parallel arrays of long collagen fibers give tendons their resistance and tensile properties. Thousands of collagen molecules self-assemble into fibers, but the fibers need instruction from their environment for alignment—fibers in solution are randomly arranged. The work by Canty et al. shows how long, thin plasma–membrane extensions, called fibripositors, set up this parallel pattern in prenatal mouse tendons.
Microscopy studies showed that these fibripositors received mature, fully processed collagen fibers from Golgi-to-plasma membrane carriers (GPCs). The GPCs eventually fused with the tip of the fibripositor, which then retracted, leaving behind its fiber contents. More fibers were added to others at the base of the fibripositor,...
