Juvenile Hormone Biosynthesis Gene Expression in the corpora allata of Honey Bee (Apis mellifera L.) Female Castes

Abstract

Juvenile hormone (JH) controls key events in the honey bee life cycle, viz. caste development and age polyethism. We quantified transcript abundance of 24 genes involved in the JH biosynthetic pathway in the corpora allata-corpora cardiaca (CA-CC) complex. The expression of six of these genes showing relatively high transcript abundance was contrasted with CA size, hemolymph JH titer, as well as JH degradation rates and JH esterase (jhe) transcript levels. Gene expression did not match the contrasting JH titers in queen and worker fourth instar larvae, but jhe transcript abundance and JH degradation rates were significantly lower in queen larvae. Consequently, transcriptional control of JHE is of importance in regulating larval JH titers and caste development. In contrast, the same analyses applied to adult worker bees allowed us inferring that the high JH levels in foragers are due to increased JH synthesis. Upon RNAi-mediated silencing of the methyl farnesoate epoxidase gene (mfe) encoding the enzyme that catalyzes methyl farnesoate-to-JH conversion, the JH titer was decreased, thus corroborating that JH titer regulation in adult honey bees depends on this final JH biosynthesis step. The molecular pathway differences underlying JH titer regulation in larval caste development versus adult age polyethism lead us to propose that mfe and jhe genes be assayed when addressing questions on the role(s) of JH in social evolution.

Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

“…The JH titer and/or JH biosynthetic gene expression is known to be affected by nutritional conditions in M. sexta, Ae. aegypti, D. melanogaster and A. mellifera (Bomtorin et al 2014;Cymborowski et al 1982;Noriega 2004;Tu et al 2005). These results imply a crosstalk between nutritional signals and the JH biosynthetic pathway, and such interactions may also be important mechanisms to regulate presoldier differentiation in Z. nevadensis.…”

“…Based on the EST libraries derived from the corpora allata and corpora cardiaca of three insect species (cockroach Diploptera punctata Eschscholtz and mosquitoes Aedes aegypti L. and Anopheles albimanus Weidemann), JH biosynthetic genes were identified, and the expression of at least six genes was examined (Noriega et al 2006). The expression of JH biosynthetic genes was also observed in the corpora allata and corpora cardiaca of the honeybee Apis mellifera L. (Bomtorin et al 2014). Moreover, based on an EST library derived from multiple tissues of the silkworm moth Bombyx mori L., eight genes in the mevalonate pathway were identified, and specific expression in the corpora allata was elucidated (Kinjoh et al 2007; Ueda et al .…”

“…For example, knockdown of JHAMT by RNA interference (RNAi) resulted in a lower level of JH synthesis in the corpora allata in the desert locust Schistocerca gregaria Forsskål (Marchal et al 2011). A decrease in the JH titer in A. mellifera was also achieved by JHAMT RNAi (Bomtorin et al 2014). CYP15A1, encoding JH epoxidase (Helvig et al 2004), converts methyl farnesoate into JH III, and RNAi resulted in an increase in the level of methyl farnesoate in the corpora allata and a decrease in the JH titer in S. gregaria (Marchal et al 2011).…”

Differential expression of miRNAs related to caste differentiation in the honey bee, Apis mellifera

“…Dozens of JH-related genes, which involved in JH signaling, biosynthesis, and metabolism, have been recently identified in the honey bee genome (Bomtorin et al 2014;Cheng et al 2014). One of them is juvenile hormone acid methyltransferase (NCBI Reference Sequence database: XM_001119986), which is differentially expressed during the caste differentiation .…”

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

“…We selected the methyl farnesoate epoxidase gene ( MFE ) as an indicator of JH production, since the expression levels of this gene, coding for the enzyme that catalyzes the final step of JH III biosynthesis, are known to be correlated with JH titers, e.g., in honeybee workers (Bomtorin et al, 2014). MFE was also identified in a number of other insect species (Daimon and Shinoda, 2013), in which, unlike in honeybees, JH preserved its ancestral gonadotropic function reported also in bumblebees (Shpigler et al, 2014, 2016).…”