Yukiko Yamashita thought she knew the fruit-fly testis inside out. But when she carried out a set of experiments on the organ five years ago, it ended up leaving her flummoxed.

Her group had been studying how fruit flies maintain their sperm supply and had engineered certain cells involved in the process to produce specific sets of proteins. But instead of showing up in the engineered cells, some proteins seemed to have teleported to a different group of cells entirely.

Yamashita, a developmental biologist at the University of Michigan in Ann Arbor, and the postdoctoral researcher with whom she was working, Mayu Inaba, called the phenomenon “mysterious trafficking”. They were convinced it was real — but they couldn't understand how it worked. So they shelved the project until one day, more than a year later, Inaba presented Yamashita with some images of tiny tubes reaching out from one cell to another — delicate structures that might have been responsible for the trafficking. Yamashita was sceptical, but decided to dig out images from her own postdoc project 12 years earlier. Sure enough, slender spikes jutted out towards the targeted cells. “It was really eye-opening,” Yamashita says. The group published its work in 2015, arguing that the tubes help testis cells to communicate precisely, sending a message to some of their neighbours and not others1. “We thought the protein was trafficked,” Yamashita says, “but we didn't think there was an actual track.”

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