Abstract
BackgroundMost of the proteins contained in royal jelly (RJ) are secreted from the hypopharyngeal glands (HG) of young bees. Although generic protein composition of RJ has been investigated, little is known about how age-dependent changes on HG secretion affect RJ composition and their biological consequences. In this study, we identified differentially expressed proteins (DEPs) during HG development by using the isobaric tag for relative and absolute quantification (iTRAQ) labeling technique. This proteomic method increases the potential for new protein discovery by improving the identification of low quantity proteins.ResultsA total of 1282 proteins were identified from five age groups of worker bees, 284 of which were differentially expressed. 43 (15.1%) of the DEPs were identified for the first time. Comparison of samples at day 6, 9, 12, and 16 of development relative to day 3 led to the unambiguous identification of 112, 117, 127, and 127 DEPs, respectively. The majority of these DEPs were up-regulated in the older worker groups, indicating a substantial change in the pattern of proteins expressed after 3 days. DEPs were identified among all the age groups, suggesting that changes in protein expression during HG ontogeny are concomitant with different states of worker development. A total of 649 proteins were mapped to canonical signaling pathways found in the Kyoto Encyclopedia of Genes and Genomes (KEGG), which were preferentially associated with metabolism and biosynthesis of secondary metabolites. More than 10 key high-abundance proteins were involved in signaling pathways related to ribosome function and protein processing in the endoplasmic reticulum. The results were validated by qPCR.ConclusionOur approach demonstrates that HG experienced important changes in protein expression during its ontogenic development, which supports the secretion of proteins involved in diverse functions in adult workers beyond its traditional role in royal jelly production.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-665) contains supplementary material, which is available to authorized users.
Highlights
Most of the proteins contained in royal jelly (RJ) are secreted from the hypopharyngeal glands (HG) of young bees
Proteins were extracted from the HGs at five time points that corresponded to specific stages of HG activity. isobaric tag for relative and absolute quantification (iTRAQ) labeling combined with liquid chromatography (LC)-mass spectrometry (MS)/MS and Mascot searches were used to identify proteins (Sample statistics are listed in Additional file 2: Table S1)
Our results show that the changes in protein expression throughout HG development can be related to different functions other than its traditional role in royal jelly production
Summary
Most of the proteins contained in royal jelly (RJ) are secreted from the hypopharyngeal glands (HG) of young bees. We identified differentially expressed proteins (DEPs) during HG development by using the isobaric tag for relative and absolute quantification (iTRAQ) labeling technique. This proteomic method increases the potential for new protein discovery by improving the identification of low quantity proteins. Royal jelly is a protein-rich secretion that serves as food for larvae and adult queen honey bees. The amount of RJ secreted by the secretory cells is positively correlated with size of the acini [5], with undeveloped or hypertrophied cells having less activity than glands of medium size. According to the age polyethism of bees, there are two described phases of the secretory cycle: production of RJ, followed by production of enzymes such as α-glucosidase, which increases with the age of the worker bee
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