A pair of research papers published recently report findings that increase our understanding of how an organism's body size is determined and how the speed of its development is controlled. In particular, the work sheds light on the molecular and cellular pathways that act to convey information about a growing organism's size, as well as on pathways that use that information to correctly time critical transitional events during development.
The two studies are reported in Current Biology online 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.