Muscle-Bound Cells

For most of us, building up muscle comes from long hours at the gym. A recent study by Dr. Talila Volk of the Weizmann Institute's Molecular Genetics Department has shown that, on the cellular level, becoming muscle-bound is all a matter of who you bump into.

Dr. Volk is studying how embryonic cells undergo differentiation - the intriguing process in which the cells, which start out identical, specialize and eventually settle into their ultimate role in various organs and tissues. She and her team discovered that in Drosophila fruit fly embryos, muscle and tendon cells must literally bump into each other to complete the differentiation process.

Once physical contact is made, the two cell types coax each other along, establishing a molecular "dialogue" which controls their further development. First, a tendon cell, which has nearly finished differentiating, tells the muscle cell where it should connect itself. Then, it's the muscle's turn to "give orders": once the muscle cell is connected, it delivers the molecular signal that tells the tendon cell to complete its own differentiation. The result is a distinct role for each: one differentiates to become a mature tendon cell, while the other "grows up" to be part of the muscle.

Volk and graduate student Talia Yarnitzky, who report their latest findings in the October 15 issue of Genes and Development, isolated and cloned a gene that makes a hormone-like growth factor which is produced in the muscle cell and induces the tendon cell to differentiate. Volk and her team also identified the key molecules in the cascade, or chain reaction, that is set off by this growth factor to convey signals between the neighboring cells.

Interestingly, a growth factor from the same family is involved in cell differentiation in mammals. Thus, although Dr. Volk used fruit flies in her research, she believes that this study may help clarify how musculature forms in human embryos. Moreover, once muscle development is fully understood, this new information may even help doctors identify and treat embryonic problems, such as congenital defects in the body's most important muscle, the heart.