Scientists just made a significant step toward the goal of growing replacement human organs by identifying that a protein called Meox1, found in stem cells, is central to promoting muscle growth.
Figuring out how to grow our own replacement organs would bring about a health revolution. It would bring an end to the desperate tightrope of life on organ donor lists, saving the lives of thousands of people every year who can't have an organ transplant or who die while waiting for one.
Researchers from Monash University in Australia found the link by studying zebrafish, fast-growing little fish that are native to Southeast Asia and which are often used as a model for humans because of our biological similarities.
Just like us, zebrafish have two eyes, a mouth, and a brain, plus muscles, blood, bones, and teeth. Both humans and zebrafish have many of the same organs, including a kidney and a heart, and 70 percent of human genes are also found in zebrafish.
Now these zebrafish have revealed some of the secrets of how stem cells and Meox1 work.
"Prior to our work in this field, we didn't even know that these growth-specific stem cells existed or how they were used," says lead researcher Peter Currie. "Just knowing that they exist leads us to the possibility of orchestrating them, controlling them, or reactivating them to regrow damaged tissue."
Scientists have long studied organ growth in lab conditions, but how stem cells produce so much living tissue in the body has remained a mystery – and until that's solved we won't be able to grow our own replacement organs.
The study found evidence of clonal drift in zebrafish, which means the stem cells weren't dividing and growing at random, but pushing forward a small number of cloned stem cells to help muscles to grow.
In other words, only a few specific stem cells are used to grow most of the required organ tissue, and Meox1 is helping to pick those cells.
We're still some way off being able to grow hearts and livers in the lab on demand as soon as someone needs them, but scientists now have a better understanding of how our molecular gears might be shifting and whirring to produce more tissue inside the body.
This process of how organ growth gets regulated by stem cells is "one of last frontiers of developmental biology" the researchers say.
Further down the line, shining a light on these mechanisms could also help us fight damage to the body caused by diseases such as cancer.
Scientists are making steady progress in this field – last year researchers from the US managed to successfully regenerate working human heart tissue, albeit still using cells from a donated organ. Now we're another step closer, thanks to the zebrafish.
The research has been published in Cell Stem Cell.