Abstract
Simple SummaryPhytosterols are important micronutrients that are essential for production of insect molting hormones and cellular membrane integrity. Past research has shown that the key phytosterol that honey bees need is 24-methylenecholesterol. This phytosterol improves honey bee longevity and sustains brood production. Hence, it is important to understand how 24-methylenecholesterol can shape honey bee physiology by altering protein profiles of vital honey bee tissues. Nurse bees secrete glandular secretions (brood food) using hypopharyngeal and mandibular glands in their head regions. Further, it has been shown that this sterol is selectively accumulated in nurse bee heads. Thus, it is imperative to examine the protein profiles of nurse bee heads, in response to dietary 24-methylenecholesterol manipulation. In this study, groups of newly emerged nurse bees were fed with varying concentrations of dietary 24-methylenecholesterol, while the control groups received no sterol. We found that dietary sterol manipulation altered the protein profiles in nurse bee heads, with important nutritional marker proteins being upregulated in high dietary sterol groups. The important proteins identified in this study may serve as vital markers of nutritional stress related to sterols in honey bees, paving the way for future research on bee nutrition.Phytosterols are important micronutrients that are precursors of important molting hormones and help maintain cellular membrane integrity in insects including bees. Previous research has shown that 24-methylenecholesterol is a key phytosterol that enhances honey bee longevity and improves nurse bee physiology. Nurse bees have the ability to selectively transfer this sterol to developing larvae through brood food. This study examines the physiological impacts of 24-methylenecholesterol on nurse bees, by analyzing the protein profiles of nurse bee heads upon dietary sterol manipulation. Dietary experimental groups consisting of newly emerged honey bees were provided with varying concentrations of 24-methylenecholesterol for three weeks. At the end of the study, honey bees were collected and proteomic analysis was performed on honey bee heads. A total of 1715 proteins were identified across experimental groups. The mean relative abundances of nutritional marker proteins (viz. major royal jelly proteins 1, 4, 5, 7) were higher in experimental groups supplemented with higher dietary sterol concentrations, when compared with the control dietary group. The mean relative abundances of important enzymatic proteins (aminopeptidase and calcium-transporting ATPase) were higher in control groups, whereas mean relative abundances of oxysterol-binding protein and fatty acid-binding protein were higher in higher dietary sterol groups.
Highlights
Nutrition is the key to honey bee colony health and survival, ensuring individual bees are healthy to counteract detrimental impacts of pathogens, parasites and pesticides [1,2,3,4]
Other groups observed were proteins that were part of extracellular regions, cell membranes and membrane structures, membrane-enclosed lumen, protein-containing complex, within the extracellular matrix, supramolecular complex and synapse (Figure 5C). To our knowledge this is the first study to report changes in the nurse bee head proteome in response to diets containing different concentrations of a key phytosterol (24-methylenecholesterol)
Previous studies have shown high quantities of 24-methylenecholesterol in the hypopharyngeal glands of honey bees that consumed an artificial diet containing this particular sterol [13]. This may have significant implications, as hypopharyngeal glands are the sites of MRJP1 production [31], and MRJP1 was more abundant in bees fed sterol-rich diets in our current study
Summary
Nutrition is the key to honey bee colony health and survival, ensuring individual bees are healthy to counteract detrimental impacts of pathogens, parasites and pesticides [1,2,3,4]. Poor nutrition is cited as one of the important factors for global bee declines. Pollen and nectar are the two important sources of nutrition, with pollen providing vital macronutrients Micronutrients such as phytosterols [5,6]. Micronutrients are important for optimal nutrition and sustenance of honey bees. Of these micronutrients, phytosterols play a critical role as precursors of insect molting hormones and assist in maintaining insect cellular membrane integrity [7,8]. Bees are sterol auxotrophs [8,9], they are dependent on pollen for their vital phytosterol needs
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