Juvenile hormone degradation enzymes in insect development: emerging insights from functional genetics

Development, physiology, and reproduction in insects require juvenile hormones (JHs). Given such essential functions, the availability of these potent small molecules is tightly controlled by synthesis, transportation, and degradation. Insects possess two classes of enzymes to degrade JHs: the canonically extracellular JH esterases (JHEs) and intracellular JH epoxide hydrolases (JHEHs). While the biochemical activities of JHEs and JHEHs have been investigated in over sixty insect species in the last 50 years, functional studies have been hindered, until recently, by extensive genetic redundancies. This review highlights how increased availability of 'omics datasets and advances in genetic manipulation have revealed novel and sometimes unexpected insights into the functions of each class of JH degradation enzyme during development and beyond. These studies provide the tools and framework to not only answer many longstanding questions regarding where, when, and how each JH degradation enzyme regulates JH availability, but also hold promise to reveal the molecular mechanisms by which JHs impart diverse functions across development.