Imaginal disc

Department of Zoology University of Wisconsin, Madison Madison, Wisconsin 53706 

Figu re 10.1. Schematic representation of late third-instar larvae, showing the approximate locations and shapes of the imaginal discs. (Reprinted, with permission, from Bodenstein 1950.) 

FRT marker FRT Low level heat shock with hsp-FLPase 

Target gene transcription in GAL4-FLPout cells 

As most crosses for generating mosaic clones generate several different genotypes, it is often more efficient to screen out the inappropriate larvae before dissection and staining. 

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This mode of regulation seems appropriate to the ERTs since their cells are already terminally differentiated, and their primary function is to grow and provide a nutrient rich incubator for the undifferentiated neuroblasts and imaginal cells that eventually produce the reproductive adult. The response of these undifferentiated progenitor cells to food withdrawal is quite unlike that of the ERTs. Larval neuroblasts and imaginal disc cells continue to proliferate for many days after a larva is starved, and seem to complete their normal proliferation programs. In this instance the ERTs lose mass, presumably as they transfer stored nutrients to the developing nervous system and the discs. 

Cells in the developing imaginal discs, which form much of the adult body during metamorphosis, exhibit a cell cycle that incorporates both modes of control described above (Fig. 2C). Each imaginal disc has 10-50 cells in the newly... 

Fain MJ, Stevens B 1982 Alterations in the cell cycle of Drosophila imaginal disc cells precede metamorphosis. Dev Biol 92 247-258... 

Weinkove D, Neufeld TP, Twardzik T, Waterfield MD, Leevers SJ 1999 Regulation of imaginal disc cell size, cell number and organ size by Drosophila class IA phosphoinositide 3-kinase and its adaptor. Curr Biol 9 1019-1029... 

Bryant As you showed on the growth curve for the imaginal disc, there is something that happens at the end of its development that stops both growth and proliferation. When you do your cell cycle analysis, is this in discs that have shut down at that point or in discs that are still in the growth phase ... 

Edgar We haven t got to the exit phase yet in the wing. Technically this is harder to get at. All our analyses have been done in second and third instar imaginal discs which are still growing but which are starting to slow down. 

Edgar The larva is a fully functional animal made up of terminally differentiated cells, but its purpose is to be an incubator for these imaginal discs that make the fly. It has to bulk up on mass and it transfers this biomass to the discs as they grow. I think it is a really simple way for an organism that is already differentiated to grow. It is a sort of stripped-down cell cycle that can respond to nutrition. There is no need for those cells to proliferate. 

Edgar With the imaginal disc cells that we have studied we can block the cell cycle pretty specifically with a Cdc25 mutation or cyclin E mutation. The cells continue to grow and eventually will die. 

Regulation of Drosophila imaginal disc growth by the insulin/IGF signalling pathway... 

Nasmyth There is a classic experiment to address whether there is size control. That is to transiently delay the cell cycle so that you produce abnormally large cells. Then you look at the cell division time of subsequent cycles. If these experiments are done with bacteria or yeast, the subsequent cycles are greatly accelerated. These experiments could be done by Bruce Edgar and his imaginal discs. They are technically harder, but they could be done. 

Nurse Peter Bryant, didn t you take bits out of the imaginal disc and then found that it reconstmcted the cells in between ... 

Nurse If instead of a whole dozen fates you have, let s say, just five, you end up with an imaginal disc that is smaller over all, compared with the one with all dozen. This suggests that determining the overall proper organ size requires a proper mixture of cells with all the cell fates, rather than a limited set. Would this be consistent ... 

Growth factors controlling imaginal disc growth in Drosophila... 

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