How Branching Tissues Sprout and Grow in Fruit Flies

Release Date:
Doris Brody, NIGMS

Intricate systems of branched tissue provide air, blood, and other critical substances to multicellular organisms. These branched systems grow out of the undifferentiated cells that form the early embryo. Because respiratory and circulatory system branching seems to follow relatively fixed patterns, developmental biologists expect that a specific genetic program controls it. Understanding such a program in humans might enable scientists to regenerate branched tissues, such as those damaged by emphysema and atherosclerosis.

NIGMS grantee Dr. Mark Krasnow and his colleagues at the Stanford University School of Medicine have taken an important step forward in understanding the genetic basis of branching. They identified a gene called branchless ( bnl) in fruit flies that is required for the proper branching of a network of fly respiratory tubes called the trachea. The protein is expressed at precise times in clusters of cells that surround the developing tracheal system cells and at the place where each new branch will form and grow out.

Dr. Krasnow's group showed that bnl triggers branching and guides it, as well. When they engineered flies so that the bnl protein appeared in specific places, branches were made in those places. When they engineered the flies to make bnl generally throughout the fly embryo, the whole embryo was filled with a tangle of branches.

One of the most interesting aspects of this research is that the bnl protein is very similar to an important family of proteins called fibroblast growth factors (FGFs) that are found in mammals, including humans. FGFs play a role in normal cell development and differentiation into tissues, and they can also be cancer-causing oncogenes. FGF proteins have been found to be involved in mammalian branching, but their roles in these processes are unclear. Understanding these roles is a first step toward developing a technique that might make the regeneration of branched tissue in humans possible.


Sutherland D, Samakovlis C, Krasnow MA. Branchless encodes a Drosophila FGF homolog that controls tracheal cell migration and the pattern of branching. Cell 1996;87:1091-1101.

Reporters may call the NIGMS Office of Communications and Public Liaison at (301) 496-7301 to obtain the name of a scientist in the NIGMS Division of Genetics and Developmental Biology who can comment on this work.