Biogenic Amine Signaling Systems in the Red Imported Fire Ant

General and Comparative Endocrinology xxx (2018) xxx–xxx

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General and Comparative Endocrinology

journal homepage: www.elsevier.com/locate/ygcen

Research paper Biogenic amine signaling systems in the red imported ﬁre ant, Solenopsis invicta – Possible contributors to worker division of labor ⇑ ⇑ Yi-xiang Qi , Tian zeng, Lei Wang, Yong-yue Lu

Department of Entomology, College of Agriculture, South China Agricultural University, Guangzhou, China article info abstract

Article history: The red imported fire ant, Solenopsis invicta Buren, is a dangerous invasive pest in the United States, China Received 23 November 2017 and other countries. Efficient division of labor is one of the main reasons for the success of this social Revised 5 March 2018 insect. Biogenic amines are important regulators of worker division of labor in this eusocial insect, but Accepted 7 March 2018 the related molecular mechanisms are largely unknown. In this study, we identified 10 candidate bio- Available online xxxx genic amine synthetic enzyme genes and 17 candidate biogenic amine receptor genes in the genome of S. invicta. Quantitative real-time PCR results indicated that foragers had higher head transcripts levels Keywords: of all the tested enzyme genes than nurses did. In the abdomen, only the rate-limiting enzyme genes for Biogenic amine the biosynthesis of serotonin and dopamine were higher in foragers than in nurses. Among the tested Enzyme Receptor serotonin receptors, only the expression of 5-HT2A gene showed significant difference between foragers Division of labor and nurses. In the head, more abundant 5-HT2A transcripts were detected in foragers than in nurses. Foragers expressed higher Octb4R than nurses in the head and abdomen. However, much lower mRNA levels of Dop3 receptor gene were detected in both body regions of foragers than nurses. Several other octopamine and tyramine receptor genes were also differentially expressed between foragers and nurses in the head and/or in the abdomen. Our results will improve the understanding of molecular mechanisms underlying biogenic amine modulation of the worker division of labor in S. invicta. Ó 2018 Elsevier Inc. All rights reserved.

1. Introduction 5-hydroxytryptophan (5-HTP) via tryptophan hydroxylase. Then, AADC converts 5-HTP into 5-HT (Fig. 1A). Tryptophan hydroxylase Biogenic amines are important neuroactive molecules in the is encoded by the phenylalanine hydroxylase (TPH) gene or trypto- central nervous system of both vertebrates and invertebrates. They phan hydroxylase (TRH) gene in Drosophila melanogaster (Coleman function as neurotransmitters, neuromodulators, and neurohor- and Neckameyer, 2005). TPH is expressed in non-neural tissues, mones to modulate multiple physiological and behavioral pro- while TRH is expressed in the neural tissues (Neckameyer et al., cesses, such as emotions, aggression, circadian rhythms and 2007). So far, five 5-HT receptors including 5-HT1A, 5-HT1B,5- locomotion (Beaulieu and Gainetdinov, 2011; Farooqui, 2012; HT2A, 5-HT2B and 5-HT7 were identified in Drosophila (Verlinden Nichols and Nichols, 2008). In insects, the actions of biogenic ami- et al., 2015). Based on the data from characterized insect 5-HT nes, including serotonin (5HT), octopamine (OA), tyramine (TA) receptors, most insects seem to possess one 5-HT7 type serotonin and dopamine (DA), are mediated via specific membrane proteins receptor, but may possess two 5-HT1 and/or two 5-HT2 receptors that primarily belong to the superfamily of G-protein-coupled (Verlinden et al., 2015)(Fig. 1D). However, A. mellifera possess only receptors (GPCR), the stimulation of which leads to the subsequent one 5-HT1 receptor (Hauser et al., 2006; Thamm et al., 2010). The changes of the intracellular concentrations of second messengers, 5-HT1 receptors couple preferentially to Gi/o proteins and inhibit including cyclic adenosine monophosphate (cAMP) and calcium cAMP synthesis. The 5-HT2 receptors couple preferentially to 2+ (Ca )(Blenau and Baumann, 2001). Gq/11 proteins, which mediate the hydrolysis of inositol phosphates 2+ 5-HT synthesis requires two enzymes, tryptophan hydroxylase and a subsequent increase in cytosolic Ca levels. The 5-HT7 and aromatic L-amino acid decarboxylase (AADC) (Fig. 1A). As receptors couple preferentially to Gs proteins and promote cAMP the first step of 5-HT synthesis, tryptophan is converted to formation (Blenau and Baumann, 2001)(Fig. 1D). OA biosynthesis from tyrosine is a two-step process in a de novo pathway (Fig. 1B). In the first step, tyrosine is decarboxylated ⇑ Corresponding authors. E-mail addresses: [email protected] (Y.-x. Qi), [email protected] to TA by tyrosine decarboxylase (TDC). In the second step, TA is (Y.-y. Lu). hydroxylated on the b-carbon of the side chain to OA by tyramine https://doi.org/10.1016/j.ygcen.2018.03.012 0016-6480/Ó 2018 Elsevier Inc. All rights reserved.

Please cite this article in press as: Qi, Y.-x., et al. Biogenic amine signaling systems in the red imported ﬁre ant, Solenopsis invicta – Possible contributors to worker division of labor. Gen. Comp. Endocrinol. (2018), https://doi.org/10.1016/j.ygcen.2018.03.012 2 Y.-x. Qi et al. / General and Comparative Endocrinology xxx (2018) xxx–xxx

Fig. 1. The biosynthesis pathway of biogenic amines and their receptor types in insects. (A) The biosynthesis pathway of serotonin. (B) The biosynthesis pathway of tyramine and octopamine. (C) The biosynthesis pathway of dopamine. (D) Classification schemes of serotonin receptors. (E) Classification schemes of tyramine and octopamine receptors. (F) Classification schemes of dopamine receptors. Abbreviations: TRH, tryptophan hydroxylase; TPH, phenylalanine hydroxylase; AADC, aromatic L-amino acid decarboxylase; TDC, tyrosine decarboxylase; TbH, tyramine b-hydroxylase; TH, tyrosine hydroxylase; DDC, DOPA decarboxylase; ebony, NBAD synthase; aaNAT, arylalkylamine N-acetyl transferase; Ca2+, calcium; cAMP, cyclic adenosine monophosphate; ", increase; ;, decrease. b-hydroxylase (TbH) (Blenau and Baumann, 2001). Tyrosine decar- thase (ebony) and arylalkylamine N-acetyl transferase (aaNAT) to boxylase is encoded by two genes dTdc1 and dTdc2 in D. melanoga- produce pigments other than melanin. NBAD hydrolase (tan) cat- ster. Both gene products have TDC activity in vivo. dTdc1 is alyzes the reaction in the opposite direction to ebony, increasing expressed non-neurally, while dTdc2 is expressed neurally (Cole dopamine concentration (Christie et al., 2014)(Fig. 1C). ebony, et al., 2005). Insect OA receptors are grouped into three classes: aaNAT and tan also participate in the inactivation of biogenic amines a-adrenergic-like receptors (Oct a-R), b-adrenergic-like receptors (Amherd et al., 2000; Denno et al., 2016). Currently, three classes of (Oct b-R) and octopamine/tyramine or tyramine receptors (TyrR) dopamine receptors have been characterized in insects (Fig. 1F). (Evans and Maqueira, 2005)(Fig. 1E). For the class of Oct a-R, Dop1 and Dop2 are functionally D1-like and increase cAMP levels two receptor types (Octa1R and Octa2R) have been characterized upon activation (Mustard et al., 2005; Xu et al., 2017). In contrast, in Drosophila and other insect species (Grohmann et al., 2003; Dop3 are functionally D2-like, in that they decrease cAMP levels Han et al., 1998; Huang et al., 2007, 2010, 2012; Qi et al., 2017; (Mustard et al., 2005; Xu et al., 2017). The third class of receptor that Wu et al., 2014). Three genes have been characterized that encode interacts with both dopamine and ecdysone (DopEcR) has been char- b-type OA receptors generating cAMP signals in Drosophila (Balfanz acterized in D. melanogaster (CG18314) (Srivastava et al., 2005). et al., 2005; Maqueira et al., 2005). Four genes coding for b-type OA CG13579 is an orphan gene. Based on the sequence similarities receptors have been identified and characterized in A. mellifera and phylogenetic relationships with other biogenic amine receptors (Balfanz et al., 2014; Hauser et al., 2006). The pharmacological (Hauser et al., 2006), we predicted it to be another DopEcR. properties of three TyrR have been characterized in Drosophila. Biogenic amines modulate various behaviors in ants, such as Orthologues of the TA3 (CG16766) receptor were only found in reproductive dominance, colony foundation, worker behavioral Drosophila species (Bayliss et al., 2013; Cazzamali et al., 2005). development, repertoire expansion, temporal polyethism, trophal- The biosynthesis of dopamine starts with the conversion of tyro- laxis, predatory aggression, nestmate recognition and subcaste- sine to L-3, 4-dihydroxyphenylalanine (L-DOPA) via the action of related division of labor (for review see Kamhi and Traniello, tyrosine hydroxylase (TH), which is the rate-limiting enzyme. L- 2013). Social insects like bees, ants and wasps often exhibit a divi- DOPA is then converted to dopamine by DOPA decarboxylase sion of labor, characterized by a differentiation in the tasks (DDC) (Christie et al., 2014). Dopamine is also utilized by NBAD syn- performed by the group members, a process that is believed to