If two cell types in a chimeric animal are unevenly matched, the stronger cell type may take over. How do they do it? Wei Li and Nicholas Baker (Albert Einstein College of Medicine, New York, NY) report that the big brutes eat their weakling competitors alive!
Cell competition, in which one cell type has a growth advantage, exists in chimeric animals. Until recently, it was assumed that the weaker cell died due to an inability to compete for nutrients and/or growth factors. In fact, as Li and Baker now show, the stronger cell type actively kills the weaker by eating it.
In fly chimeras that consisted of wild-type cells together with weaker mutant “minute” cells, Li and Baker spotted that dying minute cells were almost always inside wild-type cells. To see whether this apparent engulfment was necessary for competition, the researchers examined flies that lacked known engulfment genes. Sure enough, in chimeras with larger cells that lacked these genes, both engulfment and competition were prevented the minute cells survived.
The next step is to decipher what characterizes minute cells, such that wild-type cells recognize them as dinner.