Abstract
Over the past two decades, fundamental strides in physiology and genetics have allowed us to finally grasp the developmental mechanisms regulating body size, primarily in one model organism: the fruit fly Drosophila melanogaster. In Drosophila, as in all animals, final body size is regulated by the rate and duration of growth. These studies have identified important roles for the insulin and the target of rapamycin (TOR) signaling pathways in regulating the growth rate of the larva, the stage most important in determining final adult size. Furthermore, they have shown that the insulin/TOR pathway interacts with hormonal systems, like ecdysone and juvenile hormone, to regulate the timing of development and hence the duration of growth. This interaction allows the growing larvae to integrate cues from the environment with environmentally sensitive developmental windows to ensure that optimal size and proportions are reached given the larval rearing conditions. Results from this work have opened up new avenues of studies, including how environmental cues are integrated to regulate developmental time and how organs maintain proportional growth. Other researchers interested in the evolution of body size are beginning to apply these results to studies of body size evolution and the generation of allometry. With these new findings, and with the developments to come, the field of size control finds itself in the fortunate position of finally being able to tackle century old questions of how organisms achieve final adult size and proportions. This review discusses the state of the art of size control from a Drosophila perspective, and outlines an approach to resolving outstanding issues.
Highlights
Body size and relative proportions of organs are characteristic features that distinguish one species from the
Over the past 10 years, researchers have used the fruit fly Drosophila melanogaster to approach the problem of how development ensures that organisms achieve the appropriate body and organ size
The fat body couples the level of dietary amino acids to Drosophila produces seven insulin-like peptides (dILPs) production (Géminard et al, 2009): a reduction in developmental nutrition suppresses target of rapamycin (TOR) signaling in the fat body which in turn reduces insulin signaling in other tissues by blocking the release of dILPs
Summary
Body size and relative proportions of organs are characteristic features that distinguish one species from the next. The fat body couples the level of dietary amino acids to dILP production (Géminard et al, 2009): a reduction in developmental nutrition suppresses TOR signaling in the fat body which in turn reduces insulin signaling in other tissues by blocking the release of dILPs. While adult size results from growth during the larval feeding stage, during the wandering larval stage and the non-motile pupal stage many of the developing adult organs grow and differentiate after the cessation of feeding even though the animal does not increase in mass.
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