Histone acetylation mediates epigenetic regulation of transcriptional reprogramming in insects during metamorphosis, wounding and infection

We explored the role of HDACs and HATs in epigenetic reprogramming during metamorphosis, wounding and infection in the lepidopteran model host Galleria mellonella. We measured the expression of genes encoding components of HATs and HDACs to monitor the transcriptional activity of each enzyme complex and found that both enzymes were upregulated during pupation. Specific HAT inhibitors were able to postpone pupation and to reduce insect survival following wounding, whereas HDAC inhibitors accelerated pupation and increased survival. The administration of HDAC inhibitors modulated the expression of effector genes with key roles in tissue remodeling (matrix metalloproteinase), the regulation of sepsis (inhibitor of metalloproteinases from insects) and host defense (antimicrobial peptides), and simultaneously induced HAT activity, suggesting that histone acetylation is regulated by a feedback mechanism. We also discovered that both the entomopathogenic fungus Metarhizium anisopliae and the human bacterial pathogen Listeria monocytogenes can delay metamorphosis in G. mellonella by skewing the HDAC/HAT balance.Our study provides for the first evidence that pathogenic bacteria can interfere with the regulation of HDACs and HATs in insects which appear to manipulate host immunity and development. We conclude that histone acetylation/deacetylation in insects mediates transcriptional reprogramming during metamorphosis and in response to wounding and infection.Gene expression in eukaryotes is regulated by epigenetic mechanisms such as histone acetylation and deacetylation, which modify chromatin structure and alter the accessibility of DNA to transcription factors. The transfer of acetyl groups to and from histones is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs), which have opposing activities. The acetylation of histones by HATs increases DNA accessibility and therefore promotes gene expression, whereas HDACs reduce access to DNA and therefo