Bee castes
Honeybees live in highly structured social colonies, where the three castes have specific roles in their society that are determined biologically. The royal caste consists of a single queen bee which is supported by workers and drones.
The workers are adult female foragers which cannot reproduce. Their main functions are to gather resources from the outside world and perform various societal tasks within the colony, such as feeding the drones, cleaning the hive and packing nectar and pollen into the honeycomb cells.
The drones are sexually mature males with the specific job of mating with the queen. They have no stings and are defenceless. Once they mate, which occurs in the open air on the wing, they die immediately.
The bees communicate with each other using pheromones which are detected by chemoreceptors on hair-like structures on the antennae. These sensilla trap the odours and direct them to odorant-binding proteins within the lymph cavities in the antennae.
It is reasonable to assume that the antennal protein complements of the three castes will vary to reflect the different activities and functions of the bees. However, although there have been some studies on the subset of soluble binding proteins and other antenna-specific proteins, no comparative studies of the proteomes have been published.
This omission has been corrected by scientists in China, led by senior reporter Jianke Li with colleagues from the Key Laboratory of Pollinating Insect Biology, Ministry of Agriculture/Institute of Apicultural Research, Beijing, and the Department of Bioengineering, Zhengzhou University.
Antenna proteomes reflect different activities
The team collected the antenna from 1000 foraging workers with pollen attached and from 1000 drone bees, all of known age. The proteins were extracted before separation by two-dimensional gel electrophoresis. The protein spots were stained with a fluorescent dye for image analysis to allow comparison of the protein intensities between the drones and workers.
More than 400 proteins were visualised on the gels, of which 90 were differentially expressed between the two castes. These spots were cut out of the gels and identified by mass spectrometry, searching against the Apis mellifera (honeybee) database of the NCBI. A total of 61 proteins were identified this way, 41 being up-regulated in the drone and 20 in the workers.
Many of the raised proteins in the foraging workers were related to carbohydrate metabolism and energy production, which the researchers attributed to the strong demand for energy to allow the bees to carry out their foraging activities.
A second class of up-regulated proteins in the workers were involved with molecular transport, to allow the sensory detection and collection of nectar and pollen.
In the drones, one class of up-regulated proteins were those related to fatty acid metabolism. This was explained by the need for drones to sense and follow the fatty acid pheromones which are released by the queen during mating flight.
Antioxidant proteins were also raised in the drones, in response to the high metabolic activity and the need to curtail oxidation reactions. In addition, some proteins of this type are present to degrade the odorant proteins rapidly, so that the insects can respond to changes in their location and concentration.
Other protein classes of interest were those associated with protein folding such as the heat shock proteins, which were elevated in the drone antennae only. This was attributed to the importance of protein-protein interactions and the prevention of protein aggregation during fatty acid oxidation.
Taking the drones and workers together, antenna proteins associated with carbohydrate metabolism and energy production and molecular transport took up more than 80% of the functional enrichment analysis and 45% of the biological interaction networks produced using a protein-protein interaction predictor. This overwhelming influence serves to emphasise their importance in the olfactory functions of both castes.
The differences in the proteomes of the workers and drones adds to current knowledge of honeybee antenna and should encourage further studies of the effects of caste, gender and work program on communication on the molecular basis behind communication between bees.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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