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Small RNA expression and caste differentiation in the honeybee

ABSTRACT: Honeybees are very important eusocial insects and are involved in the pollination of many plants. Queen bees and worker bees develop from the same fertilized eggs, and are thus genetically identical despite their substantial behavioural and physiological differences. The mechanism governing developmental differences between worker and queen bees has always attracted much interest. While there are several reports on mRNA expression related to caste differentiation, no systematic investigation of small RNAs has thus far been carried out. Results: Using deep sequencing we systematically profiled small RNA expression in 4th-6th day worker larvae and queen larvae (the critical stages at which the fates of workers and queens are determined), and found that 38 miRNAs were differentially expressed between worker and queen larvae. In addition, 639 mature miRNA candidates were identified in our work for the first time, of which, 526 were expressed only in workers (318) or queens (208). Conclusion: We present the first profile of honeybee small RNAs and explore the mechanism of caste differentiation between worker and queen bees. Caste-specific expression patterns and large discrepancies in small RNA profiles between worker and queen bees indicate that small RNAs may be related to the differential development of worker and queen bee larvae. Results presented here will make a valuable contribution to understanding the caste switch between worker and queen bees.

ORGANISM(S): Apis mellifera

PROVIDER: GSE52630 | GEO | 2014/07/28

SECONDARY ACCESSION(S): PRJNA229500

REPOSITORIES: GEO

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Project description:Honeybees are very important eusocial insects and are involved in the pollination of many plants. Queen bees and worker bees develop from the same fertilized eggs, and are thus genetically identical despite their substantial behavioural and physiological differences. The mechanism governing developmental differences between worker and queen bees has always attracted much interest. While there are several reports on mRNA expression related to caste differentiation, no systematic investigation of small RNAs has thus far been carried out. Results: Using deep sequencing we systematically profiled small RNA expression in 4th-6th day worker larvae and queen larvae (the critical stages at which the fates of workers and queens are determined), and found that 38 miRNAs were differentially expressed between worker and queen larvae. In addition, 639 mature miRNA candidates were identified in our work for the first time, of which, 526 were expressed only in workers (318) or queens (208). Conclusion: We present the first profile of honeybee small RNAs and explore the mechanism of caste differentiation between worker and queen bees. Caste-specific expression patterns and large discrepancies in small RNA profiles between worker and queen bees indicate that small RNAs may be related to the differential development of worker and queen bee larvae. Results presented here will make a valuable contribution to understanding the caste switch between worker and queen bees. Three healthy 10-frame colonies of ‘Zhenongda No.1’- a high-yielding royal jelly breed of Apis mellifera ligustica , were maintained at the Huajiachi campus of Zhejiang University. In each colony, the queen laid eggs over a period of 24 hours in one empty frame which was subsequently moved to an egg-free super-chamber. After 66 hours (less than 18 hours after hatching), we transferred 150 larvae into queen cups to rear queens in each colony and put the queen cup frames into their corresponding colonies. 40-60 worker larvae and queen larvae were collected from each colony after 4 days (73~90 h after hatching), 5 days (97~114 h after hatching) and 6 days (121~138 h after hatching). The larval samples were collected into 50 ml tubes, immediately frozen in liquid nitrogen and stored at -80C until being used for RNA extraction. After total RNA was extracted and quantified , relative equal amounts of total RNAs from each of the three sampling days were pooled into respectively worker and queen samples, and the fraction of small RNAs less than 30nt long was retained and sequenced on the Illumina/Solexa high-throughput platform (HTP).

Project description:In honeybees, differential feeding of female larvae promotes the occurrence of two different phenotypes, a queen and a worker, from identical genotypes. Nutritional factors affect both endocrine responses and gene expression and, thus, change the larval developmental pattern. It is widely accepted that two types of alterations occur during this process: incremental alterations, which affect general growth, and character state alterations that result in the presence or absence of specific structures. Previous studies revealed a link between incremental alterations and differential expression of physiometabolic genes. Here, we report evidence for molecular changes that affect character states, controlling the expression of worker-like characteristics. By using cDNA microarray analyses of more than 6,000 Apis mellifera ESTs we found 240 differentially expressed genes (DEG) between developing queens and workers. Comparative analyses showed that many genes recorded as up-regulated in prospective workers appear to be unique to A. mellifera suggesting that the workers developmental pathway involves the participation of novel genes. We also show that workers up-regulate more developmental genes than queens, whereas queens up-regulate a greater predominance of physiometabolic genes. The latter include genes coding for metabolic enzymes and genes whose products are known to regulate the rate of mass-transforming processes and the general growth of the organism (e.g., tor). Many DEG are likely to be involved in processes favoring the development of caste-specific structures, like brain, legs and ovaries, as well as genes that code for cytoskeleton constituents. Treatment of developing worker larvae with juvenile hormone (JH) revealed 52 JH responsive genes, specifically during the critical period of castes development. Using Gibbs sampling and Expectation Maximization algorithms, we discovered eight overrepresented cis-elements from 4 gene groups. Graph theory and complex networks concepts were adopted to attain powerful graphical representations of the interrelation between cis-elements and genes and objectively quantify the degree of relationship between these entities. We suggest that clusters of functionally related DEGs are co-regulated during caste development in honeybees. This network of interactions is activated by nutrition-driven stimuli in early larval stages. Our data are consistent with the hypothesis that JH is a key component of the developmental determination of queen-like characters. We propose a conceptual model of caste differentiation in A. mellifera based on gene-regulatory networks. Keywords: caste differentiation during larval development; JH effect

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Small RNA expression and caste differentiation in the honeybee

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