Proteome Comparison of Hypopharyngeal Gland Development between Italian and Royal Jelly-Producing Worker Honeybees (Apis mellifera L)

The hypopharyngeal gland (HG) of the honeybee (Apis mellifera L) produces royal jelly (RJ) that is essential to feed and raise broods and queens A strain of bees (high royal jelly producing bee, RJb) has been selected for its high RJ production, but the mechanisms-of its higher yield are not understood In this study, we compared HG acini size RJ production, and protein differential expressions between the RJb and nonselected honeybee (Italian bee, ITb) using proteomics in combination with an electron microscopy, Western blot and quantitative real-time PCR (qRT-PCR) Generally the HG of both bees showed age-dependent changes in acini sizes and protein expression as worker behaviors changed from brood nursing to nectar ripening foraging, and storage activities The electron microscopic analysis revealed that the HG acini diameter of the RJb strain was large and produced 5 times more RJ than the ITb, demonstrating a positive correlation between the yield and HG acini size In addition, the proteomic analysis showed that RJb significantly upregulated a large group of proteins involved in carbohydrate metabolism and energy production those involved in protein biosynthesis development amino acid metabolism, nucleotide and fatty acid transporter, protein folding, cytoskeleton, and antioxidation, which coincides with the fact that the HGs of the RJb strain produce more RJ than the ITb strain that is owing to selection pressure We also observed age-dependent major royal jelly proteins (MRJPs) changing both-in form and expressional intensity concurrent with task-switching In addition to MRJPs, the RJb overexpressed proteins such as enolase and transitional endoplasmic reticulum ATPase, protein biosynthesis, and development proteins compared to the ITb strain to support its large HG growth and RJ secretion Because of selection pressure, RJb pursued a different strategy of increased RJ production by involving additional proteins compared to its original counterpart ITb To our knowledge, this morphological and proteomic comparison study on the HG of the two strains of worker honeybees associated with their age dependent division of labor is the first of its kind The study provided not only the quantity and quality differences in the HG from the RJb and the ITb but also addressed the cellular and behavioral biology development question of how the RJb strain can produce RJ more efficiently than its wild type strain (ITb)