Neuroendocrine cells in Drosophila melanogaster producing GPA2/GPB5, a hormone with homology to LH, FSH and TSH
Research highlights
► The glycoprotein hormone GPA2/GPB5 is a neuroendocrine hormone in Drosophila. ► In the absence of GPA2/GPB5 survival is compromised in Drosophila. ► Drosophila GPA2/GPB5 is perhaps an antidiuretic hormone.
Introduction
Many hormones and neuropeptides have homologs in both protostomes and deuterostomes and thus must be evolutionarily very old. One group of such evolutionarily old hormones is the dimers consisting of a glycoprotein A (GPA) and a glycoprotein B (GPB). The insect hormone bursicon is such a GPA/GPB dimer [23], [24], as are the vertebrate hormones LH, FSH, TSH and hCG. The vertebrate hormones share the same GPA, but each has its own GPB. Genome analysis revealed the existence of another GPA, not only in vertebrates but also in invertebrates, including insects. This new GPA, which has been called GPA2, forms a dimer with GPB5 [16], [32]. The vertebrate GPA2/GPB5 dimer has been shown to stimulate the receptors of TSH, but not those of LH or FSH, and accordingly this hormone has been named thyrostimulin [26]. Elegant work on the characterization of Drosophila GPA2/GPB5 [32] has shown that it acts through a Drosophila leucine-rich repeats-containing G protein-coupled receptor (DLGR). This receptor, DLGR1, was previously identified from Drosophila by its similarity to the vertebrate receptors for LH, FSH and TSH [15]. With the notable exception of the honeybee, genes encoding GPA2 and GPB5 dimers are present in most insect species with a completely sequenced genome e.g. [17], [18], [22], [31].
It is an interesting question as to where this hormone is produced and what its function may be in insects. Drosophila melanogaster has become an ever more important model for insect neuropeptides and neurohormones and many of its neuroendocrine cells have been identified over the last decade [27], [29], [34]. This suggests that the identification of the cells producing GPA2/GPB5 may yield clues as to its function.
Section snippets
Flies
Drosophila melanogaster was maintained in the laboratory at 25 °C in a 12 h dark/12 h light cycle on a standard corn meal feed. Jean-René Martin donated w−; UAS-bax, UAS-GFP/CyO, other fly stocks were obtained from the Bloomington Drosophila Stock Center (Bloomington, Indiana, USA).
Generation of transformants
To generate the GPB5-gal4 flies, the putative promoter of Drosophila GPB5 gene was amplified by PCR from genomic DNA using the following primers: 5′-CGCGAATTCGAAGGACGGTTGTGACAGGT-3′ and
Results
The antiserum to part of Drosophila GPB5 gave some background labeling, particularly in the fat body, however, within the central nervous system, labeling appeared specific although very weak (Supplementary data, Fig. 1), but it was different from that obtained with the flies that express gal4 under control of the putative promoter of GPB5 (Fig. 1). To resolve the ambiguity in the localization of the endocrine cells producing this hormone, we used in situ hybridization to establish which of
Discussion
Antisera do not always have the specificity one hopes for. Although our GPB5 antiserum turned out to be useless for immunohistology, the combination of GPB5-gal4 transgenic flies and in situ hybridization permitted us to demonstrate where the neuroendocrine cells producing this hormone are localized. The in situ hybridization allowed us to demonstrate that GPA2 and GPB5 are produced by the same abdominal neuroendocrine cells. These experiments also showed that the expression revealed by the
Acknowledgments
We thank two anonymous reviewers for their constructive criticism on the manuscript, Jean-Luc Morel for help with microscopy and an aliquot of rhodamine-labled phalloidin, Anne-Émilie Allain for Cy5-labeled anti-rabbit IgG, Jean-René Martin for UAS-Bax,UAS-GFP flies, Heinrich Dircksen for CCAP antiserum, the Bloomington stock center for fly stocks and BestGene for fly transformation. This work was funded by institutional operating funds from the CNRS while AS was supported by a scholarship from
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