Imagine a three-year-old with toys. Now picture a seven-year-old in class. Whether it’s the senseless handling of toys or the inability to stay quiet, there is no doubt that there are stereotypical behaviors people attribute to others. The big question remains: are our behaviors determined by nature or nurture? In other words, can our genes predict how we behave?
Yehuda Ben-Shahar, Assistant Professor in biology at Washington University in St. Louis, addresses this question through the study of honeybees. The results point to the significance of miRNAs as key regulators of behavior. Moreover, comparisons between honeybees and other insects, such as wasps and ants, suggest that social insects collectively share miRNAs absent in solitary ones.
The relatively recent discovery of miRNAs, which are tiny noncoding RNA sequences about 22 nucleotides long, render them as rather mysterious biological units with a wide array of possible functions. In light of recent studies on their involvement in nervous system functions, Ben-Shahar questions their possible role in behavior regulation.
Worker honeybees have a set sequence of tasks that they perform depending on their age. A few days after birth, a worker bee takes on the role of a nurse bee, which involves feeding larvae and secreting beeswax. A week later, the worker bee faithfully takes on other tasks, such as grooming other bees and ventilating the nest. With such a strict division of labor, honeybees naturally become Ben-Shahar’s ideal model organism.
While there is a strict protocol of task assignments, honeybees are also flexible enough to adjust their behaviors based on labor shortages, even if it means doing the same task past the typical age range. This plasticity adds to the appeal of honeybees as behavioral models.
Without previous research regarding this topic, Ben-Shahar designed his methods to study all possible miRNA in these bees’ heads. They extracted and sequenced all the small RNA fragments. After a series of sorting procedures, the researchers eventually narrowed down the sample to 97 miRNA fragments, including 17 novel ones.
Of the 97 isolated miRNA, five were selected for a behavioral experiment. In the study, scientists cultivated two colonies of bees of the same age. However, one colony was young foragers and the second was old nurses. Subsequently, they determined the level of expression of miRNAs in each colony.
Results showed that four of the five studied miRNAs were expressed at higher levels in foragers compared to nurses. Considering the fact that miRNA usually suppresses gene expression, this finding suggests that some genes transcribed in nurse bees were silenced in the foragers.
Taking a step back, researchers wondered whether miRNA could be generalized to the regulation of social behaviors as a whole. Honeybees are eusocial insects, meaning that individual bees make up colonies that function as “superorganisms.” If miRNAs speak to social creatures as a whole, perhaps similar ones are shared across species.
In a follow-up study, researchers found 19 miRNAs shared between honeybees and other eusocial insects. Moreover, five miRNAs were found only in eusocial insects and not in any other species.
miRNAs are great markers that can be used to map evolutionary relationships because they assume stable functional roles in animal genomes. Considering the importance of miRNA in regulating social behaviors, one can’t help but wonder whether or not these findings can be extended to humans. Unfortunately, Ben-Shahar doesn’t have any definite answers yet. In light of the complexity of human behaviors and the nearly 2,000 miRNA, more time is definitely needed to say anything for certain.
