Core histone modifications play an important role in chromatin remodeling and 
transcriptional regulation. Histone acetylation is one of the best-studied gene 
modifications and has been shown to be involved in numerous important biological 
processes. Herein, we demonstrated that the depletion of histone deacetylase 3 
(Hdac3) in Drosophila melanogaster resulted in a reduction in body size. Further 
genetic studies showed that Hdac3 counteracted the organ overgrowth induced by 
overexpression of insulin receptor (InR), phosphoinositide 3-kinase (PI3K) or S6 
kinase (S6K), and the growth regulation by Hdac3 was mediated through the 
deacetylation of histone H4 at lysine 16 (H4K16). Consistently, the alterations 
of H4K16 acetylation (H4K16ac) induced by the overexpression or depletion of 
males-absent-on-the-first (MOF), a histone acetyltransferase that specifically 
targets H4K16, resulted in changes in body size. Furthermore, we found that 
H4K16ac was modulated by PI3K signaling cascades. The activation of the PI3K 
pathway caused a reduction in H4K16ac, whereas the inactivation of the PI3K 
pathway resulted in an increase in H4K16ac. The increase in H4K16ac by the 
depletion of Hdac3 counteracted the PI3K-induced tissue overgrowth and 
PI3K-mediated alterations in the transcription profile. Overall, our studies 
indicated that Hdac3 served as an important regulator of the PI3K pathway and 
revealed a novel link between histone acetylation and growth control.