Tunneling nanotubes enable intercellular transfer in zebrafish embryos.

Tunneling nanotubes (TNTs) are thin intercellular connections that facilitate the transport of diverse cargoes, ranging from ions to organelles. While TNT studies have predominantly been conducted in cell cultures, the existence of open-ended TNTs within live organisms remains unverified. Despite the observation of intercellular connections during embryonic development across various species, their functional role in facilitating material transfer between connected cells has not been confirmed. In this study, we performed mosaic labeling of gastrula cells in zebrafish embryos to demonstrate the coexistence of TNT-like structures alongside other cellular protrusions. These embryonic TNT-like connections exhibited a morphology similar to that of TNTs described in cell culture, appeared to have similar formation mechanisms, and could be induced by Eps8 overexpression and CK666 treatment. Most notably, we demonstrated their capability to transfer both soluble cargoes and organelles, thus confirming their open-endedness. This study demonstrates the existence of functional, open-ended TNTs in a living embryo.