Making tendons

Cells are fastidious about their internal conditions. But for scientists trying to decipher how collagen forms structures such as tendons and the cornea, the big question 30 years ago was how much control cells exert over their surroundings. In a tendon, for example, collagen molecules join end-to-end to yield fibrils, which line up alongside one another to create bundles. These amalgamations, in turn, cluster into fascicles. Most researchers thought that cells did little to aid the process beyond manufacturing collagen, according to Robert Trelstad (Robert Wood Johnson Medical School, Piscataway, NJ). The prevailing view, he says, “was that all the cell had to do was squirt this stuff [collagen molecules] into the intercellular space and—voila!—it would self-assemble.” Trelstad expressed his disagreement with that explanation in a ditty:

It took a decade to amass...