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Tuesday, April 24, 2012

Honeybee jobs may depend on miRNAs

There are a variety of occupations within a colony of honeybees (Apis mellifera). The best known is that of queen, a position that is held by one individual from birth to death. The rest of the work details are sorted by age rather than aptitude. All bees start out caring for larvae (nurse bees), progress through food preparation, go on to maintain and protect the hive and finally, if they live long enough, become foragers collecting nectar and pollen.

It turns out that age isn’t the only thing distinguishing nurse bees from foragers.  Yehuda Ben-Shahar of Washington University, St. Louis and his colleagues have shown that different bee work assignments are associated with different levels of specific non-coding microRNAs (miRNAs). These snippets of RNA, usually just over 20 nucleotides long, are known to play important roles in regulating gene expression. In bees, they appear to be involved in the progression from one task to another.

The scientists were able to use information from the previously sequenced honeybee genome to identify 97 miRNAs in the heads of honeybees. A few of these miRNAs were present in different amounts in foragers versus in nurses. This held true even when colonies were artificially manipulated to cultivate exceptionally old nurse bees, indicating that the differences were a function of behavior rather than being strictly due to age.

Even more interesting, many of the miRNAs were present only in the brains of eusocial insects (colony insects such as bees, ants and termites). The researchers identified four miRNAs that are present in various species of bee, but not in solitary wasps. Taken together, these data suggest that miRNAs may have played a role in the evolution of the division of labor that is the hallmark of eusociality.