Fused cells with multiple nuclei are found in skeletal muscles, bone, the placenta, liver and other organs. Recently, scientists have identified a protein in nematode worms that encourages two or more normal cells with one nucleus to fuse into a single giant cell with multiple nuclei, a widespread but little understood phenomenon in biology.

The new discoveries shed light on the research of fusing therapeutic stem cells or cells carrying replacement genetic parts to cells that are damaged or diseased. "If you could deliver a necessary protein or gene to diseased muscle cells by fusing cells that carry this gene, in theory you could use this technique to fix these muscles," said Benjamin Podbilewicz of the Technion - Israel Institute of Technology.

This is the first study to identify a protein linked to fusion between cells in normal animal development. Previous studies had discovered proteins that ensure viruses grip onto their target cells or promote cell fusion in cancer. The scientists identified the fusion protein, called EFF-1, in the cell membrane on the nematode worm C. elegans. In the skin of worms with mutated EFF-1, "where most fusion takes place in C. elegans, cells sort of get lost, and start making very funny structures," Podbilewicz explained.

EFF-1 inserted in insect cells grown in the lab encouraged cells to fuse together, forming giant cells with multiple nuclei. Both fusing cells must contain EFF-1 to fuse together. The fusion succeeded in more steps, one being of "half-fused" step where the cell membranes fused together, but the contents of each cell do not mix, something common with viral fusion.

This discovery could trigger more understanding about the development of some important organs in humans. "One of the biggest examples-one third of all our body weight-is the long fibers of our skeletal muscles, which form by cell fusion," Podbilewicz said.

Cell therapies could include the delivery of regenerative stem cells to diseased cells. But Podbilewichz warned that "If cells fuse, they will get more chromosomes than usual, and more chromosomes than usual can cause defects in diseases such as cancer," he said.

So far, researchers have not found a human equivalent of EFF-1. Now scientists are in the search of the human version of EFF-1, which could be tricky since the molecular structures may be very different between worms and vertebrates.