We have lift-off
The stem cells that give rise to the flight muscles in adult fruit flies have been identified.
Muscle tissues must grow and change to accommodate the needs of an animal at various stages in its life. For example, fruit flies begin life as larvae and their muscles must help them move their soft bodies. Later, when the flies mature into adults, the muscles must provide power for flight and support for the insects’ external skeletons.
Like other animal tissues, muscles develop from non-specialized “stem cells”: at first these cells have the potential to become almost any type of cell, but later they change to become more specialized. Studies of fruit flies, in particular, have yielded insights on how pools of stem cell are created and regulated. Fruit flies are small and easier to study than larger organisms, so scientists have learned a lot about the genetics and cell biology of these flies. Rajesh Gunage and colleagues have now identified the pools of stem cells that develop into flight muscle tissue, and found that these cells were set aside for the muscles when the fruit fly embryo was still developing.
Fruit flies have large forewings that provide the power needed for flight, and small hindwings that help the insect to balance when flying. Gunage and colleagues found that a small number of cells are set aside to make the tiny muscles that will move the hindwings. A similar small number of cells are set aside to make the much larger flight muscles that move the forewings, but these cells divide more times to produce far more muscle “progenitor” cells than their hindwing counterparts: indeed, they make a couple of thousand cells that eventually fuse to form muscle fibers.
Gunage and colleagues looked at how the flight muscle progenitors multiplied by genetically engineering some of the stem cells in fruit fly larvae so that when each cell divided, its two daughter cells would fluoresce with different colors. One daughter cell would glow green and the other glow red. They found that at first the cells multiply equally, with half the new cells coming from a ‘red’ stem cell and the other half from a ‘green’ cell — meaning that the number of cells increases exponentially. Later, the balance shifted so that either more red cells than green cells were produced, or vice versa. This results in a ‘linear’ increase in number of muscle progenitor cells. Furthermore, Gunage and colleagues identified the proteins that orchestrate the switch from equal to unequal multiplying of these cells at the different times points in the fruit flies’ development.
The next challenge is to see if these stem cells that form the muscles are also available for repair of mature muscle tissue after it is damaged. If this is so, these stems cells might perform a similar function to muscle satellite cells, which are found in the mature muscles of mammals and other vertebrates.
To find out more
Read the eLife research paper on which this story is based: “Identification of a new stem cell population that generates Drosophila flight muscles” (August 18, 2014).
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
