Sunday, February 05, 2006


[evomech] The control of body size in insects (Dev Biol)

[Nijhout, Developmental Biology, Sept '03]


Control mechanisms that regulate body size and tissue size have beensought at both the cellular and organismal level. Cell-level studieshave revealed much about the control of cell growth and cell division,and how these processes are regulated by nutrition. Insulin signalingis the key mediator between nutrition and the growth of internalorgans, such as imaginal disks, and is required for the normalproportional growth of the body and its various parts. Theinsulin-related peptides of insects do not appear to control growth bythemselves, but act in conjunction with other hormones and signalingmolecules, such as ecdysone and IDGFs. Size regulation cannot beunderstood solely on the basis of the mechanisms that control cell sizeand cell number. Size regulation requires mechanisms that gatherinformation on a scale appropriate to the tissue or organ beingregulated. A new model mechanism, using autocrine signaling, isoutlined by which tissue and organ size regulation can be achieved.Body size regulation likewise requires a mechanism that integratesinformation at an appropriate scale. In insects, this mechanismoperates by controlling the secretion of ecdysone, which is the signalthat terminates the growth phase of development. The mechanisms forsize assessment and the pathways by which they trigger ecdysonesecretion are diverse and can be complex. The ways in which thesehigher-level regulatory mechanisms interact with cell- and molecular-level mechanisms are beginning to be elucidated.

Full text at:

For Nijhout's latest paper (Jan '06) - see:

and a '98 paper:


Model of an Internal Evolutionary Mechanism

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