Correlated expression patterns of microRNA genes with age-dependent behavioural changes in honeybee

The hive-living honeybees (Apis mellifera) show age-dependent behavioural changes; young bees usually nurse the broods in the colony and the older bees engage in foraging activities. These developmentally regulated behavioural changes were previously shown to be correlated with genome-wide transcriptional changes in the honeybee brain. The indigenous small regulatory RNA molecules, known as microRNAs (miRNAs), are potent regulators of gene expression and also are developmentally regulated. Thus, we wanted to study if there might be correlation of differential expression of miRNA genes in the brain with age-dependent behavioural changes of the bees. We determined expression patterns of a set (n = 20) of predicted miRNA genes, by quantitative real-time PCR assays, in the brains of young and old bees that were engaged in nursing or foraging activities in the colony, respectively. Our data show correlated up-regulation of miRNA-124, miRNA-14, miRNA-276, miRNA-13b, let-7 and miRNA-13a in the young nurse bees. miRNA-12, miRNA-9, miRNA-219, miRNA-210, miRNA-263, miRNA-92 and miRNA-283 showed correlated expression patterns in the old forager bees. The modular changes of miRNA genes in the young nurse and old forager bees suggest possible roles of miRNAs in age-dependent behavioural changes in bees. The correlated expression of intronic miRNA genes and their host genes as well as of miRNA genes physically clustered in the genome are also observed.