Recipe for a Busy Bee: MicroRNAs in Honey Bee Caste Determination

Social caste determination in the honey bee is assumed to be determined by the dietary status of the young larvae and translated into physiological and epigenetic changes through nutrient-sensing pathways. We have employed Illumina/Solexa sequencing to examine the small RNA content in the bee larval food, and show that worker jelly is enriched in miRNA complexity and abundance relative to royal jelly. The miRNA levels in worker jelly were 7-215 fold higher than in royal jelly, and both jellies showed dynamic changes in miRNA content during the 4(th) to 6(th) day of larval development. Adding specific miRNAs to royal jelly elicited significant changes in queen larval mRNA expression and morphological characters of the emerging adult queen bee. We propose that miRNAs in the nurse bee secretions constitute an additional element in the regulatory control of caste determination in the honey bee.The research was supported by National Sciences Foundation of China Grant No.30630040; National Key Basic Research & Development Program 973 under Grant Nos. 2009CB825401 and 2007CB946901 to RSC, the earmarked fund for Modern Agro-industry Technology Research System (No. CARS-45-KXJ3), and a grant of the National Natural Science Foundation of China (NSFC 30571409) to SKS, and the Nature and Science Foundation Commission of Zhejiang Province (R3080306) to SKS. Zhang was supported by the Australian Research Council through the ARC Centre of Excellence in Vision Science (CE0561903). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

MIWI and piRNA-mediated cleavage of messenger RNAs in mouse testes.

The piRNA machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves piRNA-guided cleavage of transposon-derived transcripts. As many piRNAs also appear to have the capacity to target diverse mRNAs, this raises the intriguing possibility that piRNAs may act extensively as siRNAs to degrade specific mRNAs. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated piRNAs with experimentally identified cleaved mRNA fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5' end of putative targeting piRNAs. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both piRNAs and mRNA fragments, features that resemble the pattern of piRNA amplification by the 'ping-pong' cycle. Through mapping of MIWI-RNA interactions by CLIP-seq and gene expression profiling, we found that many potential piRNA-targeted mRNAs directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between piRNAs and mRNA targets and the requirement for both the slicer activity and piRNA-loading ability of MIWI in piRNA-mediated target repression. Importantly, we demonstrated that proper turnover of certain key piRNA targets is essential for sperm formation. Together, these findings reveal the siRNA-like function of the piRNA machinery in mouse testes and its central requirement for male germ cell development and maturation

Recipe for a Busy Bee: MicroRNAs in Honey Bee Caste Determination

<div><p>Social caste determination in the honey bee is assumed to be determined by the dietary status of the young larvae and translated into physiological and epigenetic changes through nutrient-sensing pathways. We have employed Illumina/Solexa sequencing to examine the small RNA content in the bee larval food, and show that worker jelly is enriched in miRNA complexity and abundance relative to royal jelly. The miRNA levels in worker jelly were 7–215 fold higher than in royal jelly, and both jellies showed dynamic changes in miRNA content during the 4^th to 6^th day of larval development. Adding specific miRNAs to royal jelly elicited significant changes in queen larval mRNA expression and morphological characters of the emerging adult queen bee. We propose that miRNAs in the nurse bee secretions constitute an additional element in the regulatory control of caste determination in the honey bee.</p></div

Novel miRNA candidates in worker and royal jelly.

<p>Only transcripts represented by more than 10 sequence reads in any sample are shown.</p

Concentration levels of 34 miRNAs in worker and royal jelly.

<p>Concentration levels of 34 miRNAs in worker and royal jelly.</p

Morphological changes in the adult queen after ingestion of miR-184 in royal jelly by the larvae.

<p><i>Note: The method for the feeding experiment is described in “Materials and methods”. The Control and miR-184 groups consisted of queen larvae reared with royal jelly in queen cups. These were fed either 5 ul DEPC-treated water (Control group) or 5 ul miR-184 (100 ng/µl) in DEPC-treated water (miR-184 group), respectively, when they were 2 days (26∼32 hrs after hatching) and 3 days (50∼56 hrs after hatching) old. The Normal worker group consisted of worker bees collected from the experimental colony during the same season.</i></p

Dynamic variation in jelly miRNA concentrations during larval development.

<p>Only miRNAs with significant (p<0.05; t-test) variation in concentration are shown. A. Royal jelly. B. Worker jelly. All concentrations are scaled to 1 on day 4 in royal jelly.</p

Composition of small RNAs in worker and royal jelly RNA samples.

<p>Composition of small RNAs in worker and royal jelly RNA samples.</p