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Gene Expression Dynamics in Major Endocrine Regulatory Pathways along the Transition from Solitary to Social Life in a Bumblebee, Bombus terrestris

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ABSTRACT

Understanding the social evolution leading to insect eusociality requires, among other, a detailed insight into endocrine regulatory mechanisms that have been co-opted from solitary ancestors to play new roles in the complex life histories of eusocial species. Bumblebees represent well-suited models of a relatively primitive social organization standing on the mid-way to highly advanced eusociality and their queens undergo both, a solitary and a social phase, separated by winter diapause. In the present paper, we characterize the gene expression levels of major endocrine regulatory pathways across tissues, sexes, and life-stages of the buff-tailed bumblebee, Bombus terrestris, with special emphasis on critical stages of the queen's transition from solitary to social life. We focused on fundamental genes of three pathways: (1) Forkhead box protein O and insulin/insulin-like signaling, (2) Juvenile hormone (JH) signaling, and (3) Adipokinetic hormone signaling. Virgin queens were distinguished by higher expression of forkhead box protein O and downregulated insulin-like peptides and JH signaling, indicated by low expression of methyl farnesoate epoxidase (MFE) and transcription factor Krüppel homolog 1 (Kr-h1). Diapausing queens showed the expected downregulation of JH signaling in terms of low MFE and vitellogenin (Vg) expressions, but an unexpectedly high expression of Kr-h1. By contrast, reproducing queens revealed an upregulation of MFE and Vg together with insulin signaling. Surprisingly, the insulin growth factor 1 (IGF-1) turned out to be a queen-specific hormone. Workers exhibited an expression pattern of MFE and Vg similar to that of reproducing queens. Males were characterized by high Kr-h1 expression and low Vg level. The tissue comparison unveiled an unexpected resemblance between the fat body and hypopharyngeal glands across all investigated genes, sexes, and life stages.

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qRT-PCR analysis of tissue-specific relative expression levels of adipokinetic hormone (AKH) across castes of B. terrestris. AKH is involved in the mobilization of lipid, carbohydrates and/or proline stores. AKH is mainly expressed in brain-CC-CA samples, but minor expression occurred also in other tissues (see main text). Data represent mean ± SEM (n = 3–5) of normalized and rescaled expression levels. (A) Heatmap: Log-scale. Bar graphs: Relative transcript levels in linear scale (B) and log-transformed scale (C). Significantly different expression levels are indicated by different letters (p < 0.05).
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Figure 9: qRT-PCR analysis of tissue-specific relative expression levels of adipokinetic hormone (AKH) across castes of B. terrestris. AKH is involved in the mobilization of lipid, carbohydrates and/or proline stores. AKH is mainly expressed in brain-CC-CA samples, but minor expression occurred also in other tissues (see main text). Data represent mean ± SEM (n = 3–5) of normalized and rescaled expression levels. (A) Heatmap: Log-scale. Bar graphs: Relative transcript levels in linear scale (B) and log-transformed scale (C). Significantly different expression levels are indicated by different letters (p < 0.05).

Mentions: AKH was expressed in brain samples, which included also CC and CA, of all investigated specimens (Figures 9A–C, Supplementary Table S2). Unexpectedly, a minor expression was also detected in other tissues. AKH expression outside of CC was previously reported in fat bodies of A. mellifera workers (Wang et al., 2012) and brain tissues (i.e., without CC-CA) of the red firebug, P. apterus, where the translated neuropeptide was also localized and quantified (Kodrík et al., 2015). However, the significance of these observations is not clear yet.


Gene Expression Dynamics in Major Endocrine Regulatory Pathways along the Transition from Solitary to Social Life in a Bumblebee, Bombus terrestris
qRT-PCR analysis of tissue-specific relative expression levels of adipokinetic hormone (AKH) across castes of B. terrestris. AKH is involved in the mobilization of lipid, carbohydrates and/or proline stores. AKH is mainly expressed in brain-CC-CA samples, but minor expression occurred also in other tissues (see main text). Data represent mean ± SEM (n = 3–5) of normalized and rescaled expression levels. (A) Heatmap: Log-scale. Bar graphs: Relative transcript levels in linear scale (B) and log-transformed scale (C). Significantly different expression levels are indicated by different letters (p < 0.05).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121236&req=5

Figure 9: qRT-PCR analysis of tissue-specific relative expression levels of adipokinetic hormone (AKH) across castes of B. terrestris. AKH is involved in the mobilization of lipid, carbohydrates and/or proline stores. AKH is mainly expressed in brain-CC-CA samples, but minor expression occurred also in other tissues (see main text). Data represent mean ± SEM (n = 3–5) of normalized and rescaled expression levels. (A) Heatmap: Log-scale. Bar graphs: Relative transcript levels in linear scale (B) and log-transformed scale (C). Significantly different expression levels are indicated by different letters (p < 0.05).
Mentions: AKH was expressed in brain samples, which included also CC and CA, of all investigated specimens (Figures 9A–C, Supplementary Table S2). Unexpectedly, a minor expression was also detected in other tissues. AKH expression outside of CC was previously reported in fat bodies of A. mellifera workers (Wang et al., 2012) and brain tissues (i.e., without CC-CA) of the red firebug, P. apterus, where the translated neuropeptide was also localized and quantified (Kodrík et al., 2015). However, the significance of these observations is not clear yet.

View Article: PubMed Central - PubMed

ABSTRACT

Understanding the social evolution leading to insect eusociality requires, among other, a detailed insight into endocrine regulatory mechanisms that have been co-opted from solitary ancestors to play new roles in the complex life histories of eusocial species. Bumblebees represent well-suited models of a relatively primitive social organization standing on the mid-way to highly advanced eusociality and their queens undergo both, a solitary and a social phase, separated by winter diapause. In the present paper, we characterize the gene expression levels of major endocrine regulatory pathways across tissues, sexes, and life-stages of the buff-tailed bumblebee, Bombus terrestris, with special emphasis on critical stages of the queen's transition from solitary to social life. We focused on fundamental genes of three pathways: (1) Forkhead box protein O and insulin/insulin-like signaling, (2) Juvenile hormone (JH) signaling, and (3) Adipokinetic hormone signaling. Virgin queens were distinguished by higher expression of forkhead box protein O and downregulated insulin-like peptides and JH signaling, indicated by low expression of methyl farnesoate epoxidase (MFE) and transcription factor Kr&uuml;ppel homolog 1 (Kr-h1). Diapausing queens showed the expected downregulation of JH signaling in terms of low MFE and vitellogenin (Vg) expressions, but an unexpectedly high expression of Kr-h1. By contrast, reproducing queens revealed an upregulation of MFE and Vg together with insulin signaling. Surprisingly, the insulin growth factor 1 (IGF-1) turned out to be a queen-specific hormone. Workers exhibited an expression pattern of MFE and Vg similar to that of reproducing queens. Males were characterized by high Kr-h1 expression and low Vg level. The tissue comparison unveiled an unexpected resemblance between the fat body and hypopharyngeal glands across all investigated genes, sexes, and life stages.

No MeSH data available.


Related in: MedlinePlus