A population of neurons that produce hugin and express the diuretic hormone 44 receptor gene projects to the corpora allata in Drosophila melanogaster

Abstract

The corpora allata (CA) are essential endocrine organs that biosynthesize and secrete the sesquiterpenoid hormone, namely juvenile hormone (JH), to regulate a wide variety of developmental and physiological events in insects. CA are directly innervated with neurons in many insect species, implying the innervations to be important for regulating JH biosynthesis. Although this is also true for the model organism Drosophila melanogaster, neurotransmitters produced in the CA‐projecting neurons are yet to be identified. In this study on D. melanogaster, we aimed to demonstrate that a subset of neurons producing the neuropeptide hugin, the invertebrate counterpart of the vertebrate neuromedin U, directly projects to the adult CA. A synaptic vesicle marker in the hugin neurons was observed at their axon termini located on the CA, which were immunolabeled with a newly‐generated antibody to the JH biosynthesis enzyme JH acid O‐methyltransferase. We also found the CA‐projecting hugin neurons to likely express a gene encoding the specific receptor for diuretic hormone 44 (Dh44). Moreover, our data suggest that the CA‐projecting hugin neurons have synaptic connections with the upstream neurons producing Dh44. Unexpectedly, the inhibition of CA‐projecting hugin neurons did not significantly alter the expression levels of the JH‐inducible gene Krüppel‐homolog 1, which implies that the CA‐projecting neurons are not involved in JH biosynthesis but rather in other known biological processes. This is the first study to identify a specific neurotransmitter of the CA‐projecting neurons in D. melanogaster, and to anatomically characterize a neuronal pathway of the CA‐projecting neurons and their upstream neurons.

Female reproductive dormancy in Drosophila melanogaster is regulated by DH31-producing neurons projecting into the corpus allatum

“…In our previous studies, we have identified several neurons projecting to various endocrine organs, including the CA of D. melanogaster (41–43). To further identify CA-projecting neurons, we conducted immunostaining experiments using antibodies against some neuropeptides, and investigated whether any of these peptidergic-cell neuronal processes innervate the CA, as described previously for the hugin-positive neurons (43). Our results demonstrated that DH31-immunoreactive fibers and varicosities were present within the CA (Fig.…”

“…The samples were incubated with a primary antibody in a blocking solution overnight at 4 °C. The primary antibodies used were as follows: chicken anti-GFP antibody (Sigma #G6539, 1:2,000), rabbit anti-RFP antibody (Medical & Biological Laboratories PM005, 1:2,000), guinea pig anti-JHAMT antibody (43) 1:1,000–2,000); rabbit anti-JHAMT antibody (78) 1:1,000), mouse anti-DH31 antibody (this study; 1:200), guinea pig anti-DH31(31) from Michael Nitabach, Yale University, USA; 1:500), and rabbit antibody against PDF of the cricket Gryllus bimaculatus (93) 1:2000). Notably, previous studies have confirmed that anti-cricket PDF antibodies cross-react with D. melanogaster PDF protein (94, 95).…”

Neuroendocrine Regulation of Reproductive Dormancy in the Fruit Fly Drosophila melanogaster: A Review of Juvenile Hormone-Dependent Regulation

“…It is possible that these neurons are also present in the adult stage and positively regulate reproductive dormancy via inhibiting JH biosynthesis. In addition, our recent study has reported new CA-projection neurons that produce the neuropeptide hugin in D. melanogaster adults, which is unexpected given that the CAprojecting hugin neurons may not have a significant impact on JH biosynthesis in the CA (Mizuno et al, 2021). Further studies would be needed to clarify the role of the CA-projecting neurons in reproductive dormancy in D. melanogaster (Figure 3B).…”

Insect PRXamides: Evolutionary Divergence, Novelty, and Loss in a Conserved Neuropeptide System

“…A closer look at individual hugin -expressing neurons in the mandibular and maxillary neuromeres of the GNG reveals that each neuron innervates one of four targets: efferent neurons project to the RG or pharyngeal dilator muscles (PH), and INs target the superior medial protocerebrum (PC) or have descending axons (VNC). All have fine processes in the dorsal GNG and TC around the esophageal foramen ( Bader, colomb et al 2007 , Bader, Wegener et al 2007 ; Mizuno et al 2021 ).…”