A donor cell (green) transferring the Cas9 protein (green) and cellular compartments known as organelles (purple) to another cell (purple) via a tube connecting the two cells together. Image credit: Zhang and Schekman (CC BY 4.0)
Communication between cells is an important process for survival, especially in multicellular organisms. Cells typically exchange information by releasing small molecules in to their surrounding environment which neighboring cells then receive and respond to. However, there is growing evidence to suggest that cells also pass signals to each other via fatty bubbles called exosomes and tubes connecting their membranes.
Various reports have suggested that these mechanisms can transport larger proteins and nucleic acids which carry the information cells need to make proteins. However, how cells are able to combine their membranes to allow these types of transfer is unclear.
To investigate, Zhang and Schekman studied how human cancer cells and embryonic cells grown in a laboratory pass molecules between each other. This included a string of nucleic acids known as RNA and a protein called Cas9 which can edit the genome of cells to activate an enzyme that has bioluminescence activity. By measuring the level of luminescence, Zhang and Schekman were able to sensitively detect the transfer of Cas9 and RNA to neighboring cells.
The experiments showed that exosomes were not efficient at transporting proteins or RNA. However, cells in near or direct contact transferred both molecules effectively using tube connections, with some cell types being more adept at this mechanism than others. Zhang and Schekman found that the formation of these tubular channels required a protein called syncytin which helps membranes fuse together mainly in the early stages of embryo development.
These findings open a new avenue of investigation on how cells send signals to one another. It is also possible that the protein syncytin has a role in cancer progression, as tumors rely on cell communication to maintain their growth and organize the cells surrounding them. However, further work is needed to investigate this possibility.
