A MicroRNA Associated With Caste Determination in a Bumblebee is Expressed from a Mirtron Within a Homologue of Vitellogenin

Our aim was to use next-generation sequencing to identify the miRNAs associated with caste determination in queen-destined and worker-destined larvae of the bumble bee, Bombus terrestris. We found that two miRNAs (miR-6001-5p and miR-6001-3p) were upregulated in queen-destined larvae that had passed the critical developmental period when caste becomes irreversible in this species. The two miRNAs form a duplex that is expressed from the gene VHDL, a homologue of Vitellogenin. This finding suggests a new connection between miRNAs and a key protein known to play multiple roles in regulating reproductive division of labour in eusocial Hymenoptera . Overall design: We made miRNA profiles from two development points (termed early-instar and late-instar) in queen-destined and worker-destined larvae of Bombus terrestris (four replicates per phenotype, making 16 libraries in total). Early-instar larvae are still capable of developing into either queens or workers, while the caste of late-instar larvae has already been determined. We then used bioinformatics methods to compare the miRNA profile between each phenotype, and isolated miRNAs that were differentially expressed.