Juvenile hormone-induced histone deacetylase 3 suppresses apoptosis to maintain larval midgut in the yellow fever mosquito

The yellow fever mosquito, Aedes aegypti, is distributed worldwide and transmits viruses that cause many diseases, including dengue, yellow fever, chikungunya, and zika. Epigenetic modifications such as acetylation of histones regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) control insect development. We recently reported that the Creb-binding protein (a HAT) regulates the metamorphosis of A. aegypti. However, the function of HDACs in A. aegypti is not known. In this study, we identified 10 genes coding for HDACs in A. aegypti and determined their function in larval development using RNA interference (RNAi). Knockdown of each HDAC has a distinct effect on the growth, development, and metamorphosis of A. aegypti. Knockdown of HDAC3 severely affected the larval survival, indicating its indispensable role in larval development. HDAC3 is highly expressed during the larval stages, and its messenger RNA (mRNA) levels correlate with the juvenile hormone (JH) titers. JH induces the expression of HDAC3 through its receptor, methoprenetolerant (Met). Knockdown of HDAC3 resulted in increased expression of proapoptotic genes involved in apoptosis of larval midgut cells. This consequently decreased midgut size and led to larval death. HDAC3 deacetylates histone H4 localized at the promoters of proapoptotic genes and suppresses their expression. In addition, a corepressor, SMRTER, is required for HDAC3-mediated suppression of proapoptotic genes. Interestingly, ecdysone attenuates HDAC3-mediated repression of proapoptotic genes. These data demonstrate that JH-induced HDAC3 is a key player in JH suppression of precocious larval cell death and metamorphosis in A. aegypti.