Crowning the Queen

The tale of the honeybee queen is a classic and popular example of developmental plasticity (aka changes in development in response to the environment). Although this is not a marine example, it is an elegant system for looking at the role of larval development in ecosystem function. Queens, worker bees and drones all have the same genome, but have very different final forms. The important determining factor in social class is eating like a queen. You are what you eat. A diet of Royal Jelly causes hormones to rage and a queen to develop. 

The role of Royal Jelly has been well established, but only now have the active ingredient(s) in the jelly and mechanism by which it works been revealed. M. Kamakura, apparently singlehandedly, discovered that a single protein, royalactin, was responsible for making a queen. Furthermore, he connected royalactin to changes in hormones through epithelial growth factor (EGF) signaling.

This work was a breakthrough in understanding the signaling mechanisms involved in drastically altering development. It identifies new players and seemingly disproved the involvement of another key player - insulin.

Researchers at Arizona State, however, were convinced of the involvement of the insulin-like signaling pathway and set out to find a unifying model for making a queen. N. Mutti and colleagues found that IRS, a protein that interacts with the insulin receptor, was essential for the action of royal jelly. Honeybee larvae lacking IRS turned into workerbees even when fed royal jelly. It appears that IRS may be the key to both EGF and insulin signaling pathways. Mutti proposes that IRS could act as alternative substrate for the EGF receptor - when larvae are fed royal jelly IRS signals through the EGF receptor and without royal jelly IRS signals through the insulin pathway providing a definitive signaling switch between the life of royalty and the short life of a busy worker.

Although more experiments are needed to show that IRS alternatively interacts with the two receptors in a diet-dependent manner, this is an elegant mechanism for controlling development and drives home the importance of signals.  Signals arguably initiate the earliest developmental processes and then fine tune the program to a final, fully functional organism.  In some ways, gene regulatory networks can be thought of as an intermediate tuning knob to achieve the right signal output. If we start to think of development in this way, it is easy to see how the environment could have such large effects on development.


References:

Kamakura, M. 2011. Royalactin induces queen differentiation in honeybees. Nature 473, 478–483 doi:10.1038/nature10093

Mutti, N. S., Dolezal, A. G., Wolschin, F., Mutti, J. S., Gill, K. S. and Amdam, G. V. 2011. IRS and TOR nutrient-signaling pathways act via juvenile hormone to influence honey bee caste fate. J. Exp. Biol. 214, 3977-3984  http://jeb.biologists.org/content/214/23/i.2