The two studies are reported in Current Biology online on September 22 by Dr. Philip E. Caldwell and colleagues of Rice University and Dr. Christen Mirth and colleagues of the University of Washington.
Previous work had shown that there is a close linkage between the final body size of an organism and the length of its developmental stages: Elephants are larger and develop more slowly than mice. However, the mechanisms by which body size and developmental rate are controlled remain incompletely understood.
Both studies examine the control of larval development in the fruit fly Drosophila. Fruit flies undergo three successive larval stages and molts before undergoing metaphorphosis and emerging as adult flies. In insects, it was previously found that the release of the hormone ecdysone from an endocrine organ called the prothoracic gland triggers larval molting and, ultimately, metamorphosis. Thus, researchers have speculated that the timing of ecdysone release is critical in determining both the final body size and developmental rate of an insect.
In their new work, Philip Caldwell, Magdalena Walkiewicz, and Michael Stern manipulated the timing and amount of ecdysone release during development of the fruit fly. They induced precocious ecdysone release by specifically expressing an activated form of the signaling molecule Ras in the endocrine prothoracic gland. This precocious ecdysone release caused flies to develop more rapidly and exhibit a much smaller body size than normal. In contrast, inhibit