A switch in the control of growth of the wing imaginal disks of Manduca sexta.

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BACKGROUND: Insulin and ecdysone are the key extrinsic regulators of growth for the wing imaginal disks of insects. In vitro tissue culture studies have shown that these two growth regulators act synergistically: either factor alone stimulates only limited growth, but together they stimulate disks to grow at a rate identical to that observed in situ. It is generally thought that insulin signaling links growth to nutrition, and that starvation stops growth because it inhibits insulin secretion. At the end of larval life feeding stops but the disks continue to grow, so at that time disk growth has become uncoupled from nutrition. We sought to determine at exactly what point in development this uncoupling occurs. METHODOLOGY: Growth and cell proliferation in the wing imaginal disks and hemolymph carbohydrate concentrations were measured at various stages in the last larval instar under experimental conditions of starvation, ligation, rescue, and hormone treatment. PRINCIPAL FINDINGS: Here we show that in the last larval instar of M. sexta, the uncoupling of nutrition and growth occurs as the larva passes the critical weight. Before this time, starvation causes a decline in hemolymph glucose and trehalose and a cessation of wing imaginal disks growth, which can be rescued by injections of trehalose. After the critical weight the trehalose response to starvation disappears, and the expression of insulin becomes decoupled from nutrition. After the critical weight the wing disks loose their sensitivity to repression by juvenile hormone, and factors from the abdomen, but not the brain, are required to drive continued growth. CONCLUSIONS: During the last larval instar imaginal disk growth becomes decoupled from somatic growth at the time that the endocrine events of metamorphosis are initiated. These regulatory changes ensure that disk growth continues uninterrupted when the nutritive and endocrine signals undergo the drastic changes associated with metamorphosis.





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Tobler, Alexandra, and H Frederik Nijhout (2010). A switch in the control of growth of the wing imaginal disks of Manduca sexta. PLoS One, 5(5). p. e10723. 10.1371/journal.pone.0010723 Retrieved from https://hdl.handle.net/10161/4540.

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H. Frederik Nijhout

John Franklin Crowell Distinguished Professor of Biology

Fred Nijhout is broadly interested in developmental physiology and in the interactions between development and evolution. He has several lines of research ongoing in his laboratory that on the surface may look independent from one another, but all share a conceptual interest in understanding how complex traits arise through, and are affected by, the interaction of genetic and environmental factors. 1) The control of polyphenic development in insects. This work attempts to understand how the insect developmental hormones, ecdysone and juvenile hormone, act to control alternative developmental pathways within a single individual. His studies and those of his students have dealt with the control of sequential polyphenism in metamorphosis, of alternate polyphenisms in caste determination of social insects and the many seasonal forms of insects. 2) The regulation of organ and body size in insects. Ongoing research deals with the mechanism by which insects asses their body size and stop growing when they have achieved a characteristic size. Other studies deal with the control of growth and size of imaginal disks. This work is revealing that the control of body and organ size does not reside in any specific cellular or molecular mechanism but that it is a systems property in which cellular, physiological and environmental signals all contribute in inextricable ways to produce the final phenotype. 3) The development and evolution of color patterns in Lepidoptera. Ongoing research attempts to elucidate the evolution of mimicry using genetic and genomic approaches. 4) The development, genetics and evolution of complex traits. Complex traits are those whose variation is affected by many genes and environmental factors and whose inheritance does not follow Mendel’s laws. In practice this involves understanding how genetic and developmental networks operate when there is allelic variation in their genes. This work attempts to reconstruct complex traits through mathematical models of the genetic and developmental processes by which they originate, and uses these models to study the effects of mutation and selection. Currently metabolic networks are being used to develop a deeper understanding of the functional relationships between genetic variation and trait variation, and of the mechanisms by which genetic and environmental variables interact to produce phenotypes. More on web page: http://www.biology.duke.edu/nijhout/

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