The Neuroproteomic Basis of Enhanced Perception and Processing of Brood Signals That Trigger Increased Reproductive Investment in Honeybee (Apis mellifera) Workers

A comparative transcriptome analysis of the head of 1 and 9 days old worker honeybees (Apis mellifera)

The role of bees in the environment, economic, biodiversity and pharmaceutical industries is due to its social behavior, which is oriented from the brain and hypopharyngeal gland that is the center of royal jelly (RJ) production. Limited studies have been performed on the head gene expression profile at the RJ production stage. The aim of this study was to compare the gene expressions in 9 and 1-day-old (DO) honeybee workers in order to achieve better understanding about head gene expression pattern. After sequencing of RNAs, transcriptome and their networks were compared. The head expression profile undergoes various changes. 1662 gene transcripts had differential expressions which 1125 and 537 were up and down regulated, respectively, in 9_DO compared with 1_DO honey bees. The day 1th had more significant role in the expression of genes related to RJ production as major RJ protein 1, 2, 3, 5, 6 and 9 encoding genes, but their maximum secretion occurred at day 9th. All process related to hypopharyngeal glands activities as CYP450 gene, fatty acid synthase gene, vitamin B6 metabolism and some of genes involved in fatty acid elongation and degradation process had an upward trend from 1_DO and were age-dependent. By increasing the age, the activity of pathways related to immune system increased for keeping the health of bees against the chemical compound. The expression of aromatic amino acid genes involved in Phenylalanine, tyrosine and tryptophan biosynthesis pathway are essential for early stage of life. In 9_DO honeybees, the energy supplying, reducing stress, protein production and export pathways have a crucial role for support the body development and the social duties. It can be stated that the activity of honeybee head is focused on energy supply instead of storage, while actively trying to improve the level of cell dynamics for increasing the immunity and reducing stress. Results of current study identified key genes of certain behaviors of honeybee workers. Deeper considering of some pathways will be evaluated in future studies.

Major royal jelly proteins influence the neurobiological regulation of the division of labor among honey bee workers

Age-based division of labor among workers is a fundamental life-history trait of many social insects, including the Western honey bee, Apis mellifera L. Extensive studies of the causation of the most pronounced transition from performing tasks in the nest to outside foraging indicate hormonal regulation of complex physiological changes. However, the proximate neurobiological mechanisms that cause the behavioral repertoire to change are still not understood and require novel approaches to be fully characterized. Thus, we established the first comprehensive monoclonal antibody microarray in honey bees with 16,320 antibodies to directly identify proteins in the brain that regulate the transition to foraging. Major royal jelly protein (MRJP) 1 and MRJP3 were identified as potential protein effectors and further investigated. A series of experimental manipulations of the workers' behavioral transition led to changes in MRJP1 and MRJP3 quantities in accordance with their presumed functional role. Injection of MRJPs into the brain resulted in increased task-reversal from foraging to nursing and decreased task-progression from nursing to foraging, while the latter was increased by injection with MRJP antibodies. Finally, down-regulation of MRJP1 and MRJP3 expression via RNAi injection into the brain increased the transition from in-hive nursing to outside foraging, confirming a causal role of these two proteins in the proximate regulation of behavior and life-history of honey bee workers. Interaction partners of MRJP1 and MRJP3 in the honey bee brain included other regulators of honey bee behavior and life history. Thus, our transformative methodological advancement of proteome analysis in honey bees reveals novel regulators of honey bee behavior, extends our understanding of the functional pleiotropy of MRJPs, and supports a general nutrition-based model of the regulation of the age-based division of labor in honey bees.

Effect of queen cell numbers on royal jelly production and quality

Royal jelly (RJ) is a popular functional food with a wealth of health-promoting effects. Over 90% of the global RJ is produced in China mainly by a high RJ-producing honeybee (RJB) strain that can accept and feed a great number of queen larvae for RJ production. To elucidate RJ changes due to queen cell numbers (QCNs), we compared the yield, larval acceptance rate, metabolic and proteomic profiles, and antioxidant activities of RJ from 1 to 5 strips of queen cells (64 per strip) in RJB colonies. As QCNs increased, the larval acceptance rate was not found to vary (p = 0.269) whereas the RJ weight per cell began to significantly decline in the 5-strip colonies (p < 0.05). Increased QCNs had a profound impact on RJ metabolic profiles and mainly reduced fatty acid levels. Remarkably, the 10-hydroxy-2-decenoic acid (10-HDA) content, a most important indicator of RJ quality, declined gradually from 2.01% in the 1-strip colonies to 1.52% in the 5-strip colonies (p < 0.001). RJ proteomic profiles were minimally altered and antioxidant activities were not significantly changed by QCNs. Collectively, the metabolomics and proteomics data and the antioxidant activity test represent a global evaluation of the quality of RJ produced with different QCNs. Our findings gain new insights into higher-quality RJ production using the high-yielding RJBs.

Genetic Drift and Purifying Selection Shaped Mitochondrial Genome Variation in the High Royal Jelly-Producing Honeybee Strain (Apis mellifera ligustica)

Mitochondrial genomes (mitogenomes) are involved in cellular energy metabolism and have been shown to undergo adaptive evolution in organisms with increased energy-consuming activities. The genetically selected high royal jelly-producing bees (RJBs, Apis mellifera ligustica) in China can produce 10 times more royal jelly, a highly nutritional and functional food, relative to unselected Italian bees (ITBs). To test for potential adaptive evolution of RJB mitochondrial genes, we sequenced mitogenomes from 100 RJBs and 30 ITBs. Haplotype network and phylogenetic analysis indicate that RJBs and ITBs are not reciprocally monophyletic but mainly divided into the RJB- and ITB-dominant sublineages. The RJB-dominant sublineage proportion is 6-fold higher in RJBs (84/100) than in ITBs (4/30), which is mainly attributable to genetic drift rather than positive selection. The RJB-dominant sublineage exhibits a low genetic diversity due to purifying selection. Moreover, mitogenome abundance is not significantly different between RJBs and ITBs, thereby rejecting the association between mitogenome copy number and royal jelly-producing performance. Our findings demonstrate low genetic diversity levels of RJB mitogenomes and reveal genetic drift and purifying selection as potential forces driving RJB mitogenome evolution.

High royal jelly production does not impact the gut microbiome of honey bees

Background

Honey bees are not only essential for pollination services, but are also economically important as a source of hive products (e.g., honey, royal jelly, pollen, wax, and propolis) that are used as foods, cosmetics, and alternative medicines. Royal jelly is a popular honey bee product with multiple potential medicinal properties. To boost royal jelly production, a long-term genetic selection program of Italian honey bees (ITBs) in China has been performed, resulting in honey bee stocks (here referred to as RJBs) that produce an order of magnitude more royal jelly than ITBs. Although multiple studies have investigated the molecular basis of increased royal jelly yields, one factor that has not been considered is the role of honey bee-associated gut microbes.

Results

Based on the behavioral, morphological, physiological, and neurological differences between RJBs and ITBs, we predicted that the gut microbiome composition of RJBs bees would differ from ITBs. To test this hypothesis, we investigated the bacterial composition of RJB and ITB workers from an urban location and RJBs from a rural location in China. Based on 16S rRNA gene profiling, we did not find any evidence that RJBs possess a unique bacterial gut community when compared to ITBs. However, we observed differences between honey bees from the urban versus rural sites.

Conclusions

Our results suggest that the environmental factors rather than stock differences are more important in shaping the bacterial composition in honey bee guts. Further studies are needed to investigate if the observed differences in relative abundance of taxa between the urban and rural bees correspond to distinct functional capabilities that impact honey bee health. Because the lifestyle, diet, and other environmental variables are different in rural and urban areas, controlled studies are needed to determine which of these factors are responsible for the observed differences in gut bacterial composition between urban and rural honeybees.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00124-1.

Identification of long noncoding RNAs reveals the effects of dinotefuran on the brain in Apis mellifera (Hymenopptera: Apidae)

Background

Dinotefuran (CAS No. 165252–70-0), a neonicotinoid insecticide, has been used to protect various crops against invertebrate pests and has been associated with numerous negative sublethal effects on honey bees. Long noncoding RNAs (lncRNAs) play important roles in mediating various biological and pathological processes, involving transcriptional and gene regulation. The effects of dinotefuran on lncRNA expression and lncRNA function in the honey bee brain are still obscure.

Results

Through RNA sequencing, a comprehensive analysis of lncRNAs and mRNAs was performed following exposure to 0.01 mg/L dinotefuran for 1, 5, and 10 d. In total, 312 lncRNAs and 1341 mRNAs, 347 lncRNAs and 1458 mRNAs, and 345 lncRNAs and 1155 mRNAs were found to be differentially expressed (DE) on days 1, 5 and 10, respectively. Gene set enrichment analysis (GSEA) indicated that the dinotefuran-treated group showed enrichment in carbohydrate and protein metabolism and immune-inflammatory responses such as glycine, serine and threonine metabolism, pentose and glucuronate interconversion, and Hippo and transforming growth factor-β (TGF-β) signaling pathways. Moreover, the DE lncRNA TCONS_00086519 was shown by fluorescence in situ hybridization (FISH) to be distributed mainly in the cytoplasm, suggesting that it may serve as a competing endogenous RNA and a regulatory factor in the immune response to dinotefuran.

Conclusion

This study characterized the expression profile of lncRNAs upon exposure to neonicotinoid insecticides in young adult honey bees and provided a framework for further study of the role of lncRNAs in honey bee growth and the immune response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07811-y.

Tachykinin signaling inhibits task-specific behavioral responsiveness in honeybee workers

Behavioral specialization is key to the success of social insects and leads to division of labor among colony members. Response thresholds to task-specific stimuli are thought to proximally regulate behavioral specialization, but their neurobiological regulation is complex and not well understood. Here, we show that response thresholds to task-relevant stimuli correspond to the specialization of three behavioral phenotypes of honeybee workers in the well-studied and important Apis mellifera and Apis cerana. Quantitative neuropeptidome comparisons suggest two tachykinin-related peptides (TRP2 and TRP3) as candidates for the modification of these response thresholds. Based on our characterization of their receptor binding and downstream signaling, we confirm a functional role of tachykinin signaling in regulating specific responsiveness of honeybee workers: TRP2 injection and RNAi-mediated downregulation cause consistent, opposite effects on responsiveness to task-specific stimuli of each behaviorally specialized phenotype but not to stimuli that are unrelated to their tasks. Thus, our study demonstrates that TRP signaling regulates the degree of task-specific responsiveness of specialized honeybee workers and may control the context specificity of behavior in animals more generally.

Multifunctionality and intrinsic disorder of royal jelly proteome

Royal Jelly (RJ) is a gelatinous white-yellowish fluid, possessing a sour taste and a slight phenolic smell that is secreted by the hypopharyngeal and mandibular salivary glands of the nurse honeybees, and is used in nutrition of larvae and adult queens. Similar to other substances associated with the activities of honeybees, RJ not only contains nutritive components, such as carbohydrates, proteins, peptides, lipids, vitamins, and mineral salts, but also represents a natural ingredient with cosmetic and health-promoting properties. RJ is characterized by remarkable multifunctionality, possessing numerous biological activities. Although this multifunctionality of RJ can be considered as a consequence of its complex nature, many proteins and peptides in RJ are polyfunctional entities themselves. In this article, we show that RJ proteins contain different levels of intrinsic disorder, have sites of post-translational modifications, can be found in multiple isoforms, and many of them possess disorder-based binding sites, suggesting that the conformational ensembles of the RJ proteins might undergo change as a result of their interaction with specific binding partners. All these observations suggest that the multifunctionality of proteins and peptides from RJ is determined by their structural heterogeneity and polymorphism, and serve as an illustration of the protein structure-function continuum concept.