Strikingly, no changes in the number of cells in the posterior compartment are detected. Thus, overexpression of Akt1 affects compartment size by altering cell growth without a concomitant increase in the final number of cells within the compartment. Studies of mammalian cells have indicated that Akt may positively regulate cell-cycle progression. Interestingly, Akt1 expression in the posterior compartment does not rescue the cells of the ZNC from their G1 arrest. As a more quantitative assay of Akt1 effects on cell-cycle progression, wing imaginal discs ubiquitously expressing Akt1 were dissected and cellular DNA content was measured by flow cytometry.
Compartments function as an independent units of growth and size control.
Ectopic expression of Akt1 overrides the intrinsic control mechanisms regulating the final size of posterior compartment. To circumvent potential compartment controls on cell number, clones of cells overexpressing Akt1 were generated in the wing imaginal disc. Clone size was assessed 48 h after induction by heat-shock. Akt1 markedly increases clonal size through an enlargement of the cells rather than an increase in the cell number. Analysis reveals that the increase in clonal size induced by ectopic Akt1 expression is due to a selective increase in cell size but not cell number.