MicroRNA regulation of stable lipid loss in honey bees, Apis mellifera

Adult workers of the Western honey bee (Apis mellifera) undergo a robust loss of abdominal lipid mass as a part of their age-related division of labor and a shift from tending brood and other jobs inside the hive to foraging outside. This lipid loss is plastic; workers can speed up or delay lipid loss depending on the needs of the colony. Once reduced, low lipid levels are maintained for the remainder of the individual’s life independent of diet or task. While key endocrine-signaling pathways, including insulin-like signaling (IIS) and juvenile hormone (JH), govern robust changes in abdominal gene expression during lipid loss, little is known about the gene regulatory mechanisms involved. MicroRNAs (miRNAs) are small non-coding RNAs that repress translation. We hypothesized that miRNAs influence lipid levels through the regulation of IIS/JH associated gene expression. To test this hypothesis, we developed antagomir (miRNA-silencing) constructs for two miRNAs, ame-miR-305 and ame-miR-375, both of which decrease fat body miRNA expression in vivo. Antagomir treatment showed that ame-miR-305 regulates a transcription factor associated with JH signaling, Krüppel homolog-1, and analyses of other relevant genes are in progress. In addition, treatment with antagomir for ame-miR-305 reduced abdominal fat body lipid mass in early summer bees, suggesting that miRNAs may coordinate worker physiological status. We anticipate that our results will contribute both to our understanding of division of labor in honey bees and the genomic mechanisms that regulate it.