Bursicon is a neurohumoral agent responsible for tanning and hardening of the cuticle and expansion of the wings during the final phase of insect metamorphosis. Although the hormonal activity was described more than 40 years ago, the molecular nature of bursicon has remained elusive. We identify here Drosophila bioactive bursicon as a heterodimer made of two cystine knot polypeptides. This conclusion was reached in part from the unexpected observation that in the genome of the honey bee, the orthologs of the two Drosophila proteins are predicted to be fused in a single open reading frame. The heterodimeric Drosophila protein displays bursicon bioactivity in freshly eclosed neck-ligated flies and is the natural agonist of the orphan G protein-coupled receptor DLGR2.

No abstract

Gene inactivation of the orphan G protein-coupled receptorLGR4, a paralogue of the epithelial-stem-cell marker LGR5, results in a 50% decrease in epithelial cell proliferation and an 80% reduction in terminal differentiation of Paneth cells in postnatal mouse intestinal crypts. When cultured ex vivo, LGR4-deficient crypts or progenitors, but not LGR5-deficient progenitors, die rapidly with marked downregulation of stem-cell markers and Wnt target genes, including Lgr5. Partial rescue of this phenotype is achieved by addition of LiCl to the culture medium, but not Wnt agonists. Our results identify LGR4 as a permissive factor in the Wnt pathway in the intestine and, as such, as a potential target for intestinal cancer therapy.

Male insects change behaviors of female partners by co-transferring accessory gland proteins (Acps) like sex peptide (SP), with their sperm. The Drosophila sex peptide receptor (SPR) is a G protein-coupled receptor expressed in the female's nervous system and genital tract. While most Acps show a fast rate of evolution, SPRs are highly conserved in insects. We report activation of SPRs by evolutionary conserved myoinhibiting peptides (MIPs). Structural determinants in SP and MIPs responsible for this dual receptor activation are characterized. Drosophila SPR is also expressed in embryonic and larval stages and in the adult male nervous system, whereas SP expression is restricted to the male reproductive system. MIP transcripts occur in male and female central nervous system, possibly acting as endogenous SPR ligands. Evolutionary consequences of the promiscuous nature of SPRs are discussed. MIPs likely function as ancestral ligands of SPRs and could place evolutionary constraints on the MIP/SPR class.

Leucine-rich repeat containing G protein-coupled receptors or LGRs are receptors with important functions in development and reproduction. Belonging to this evolutionarily conserved group of receptors are the well-studied glycoprotein hormone receptors and relaxin receptors in mammals, as well as the bursicon receptor, which triggers cuticle hardening and tanning in freshly enclosed insects. In this study, the numerous LGR sequences in different animal phyla are analyzed and compared. Based on these data a phylogenetic tree was generated. This information sheds new light on structural and evolutionary aspects regarding this receptor group. Apart from vertebrates and insects, LGRs are also present in early chordates (Urochordata, Cephalochordata and Hyperoartia) and other arthropods (Arachnida and Branchiopoda) as well as in Mollusca, Echinodermata, Hemichordata, Nematoda, and even in ancient animal life forms, such as Cnidaria and Placozoa. Three distinct types of LGR exist, distinguishable by their number of leucine-rich repeats (LRRs), their type-specific hinge region and the presence or absence of an LDLa motif. Type C LGRs containing only one LDLa (C1 subtype) appear to be present in nearly all animal phyla. We here describe a second subtype, C2, containing multiple LDLa motifs, which was discovered in echinoderms, mollusks and in one insect species (Pediculus humanis corporis). In addition, eight putative LGRs can be predicted from the genome data of the placozoan species Trichoplax adhaerens. They may represent an ancient form of the LGRs, however, more genomic data will be required to confirm this hypothesis.

Different neuroparsin variants were initially identified as anti-gonadotropic peptides from the pars intercerebralis-corpora cardiaca complex of the migratory locust, Locusta migratoria, and further studies revealed the pleiotropic activities of these peptides. Subsequently, additional neuroparsin-like peptides were discovered from other arthropod species. Studies in mosquitoes and locusts suggest that members of this conserved peptide family are involved in the regulation of insect reproduction and can even serve as molecular markers of the fascinating biological process of locust phase transition. Sequence analysis and multiple alignments revealed pronounced sequence similarities between arthropod neuroparsins and the N-terminal, growth factor binding region of vertebrate and mollusc insulin-like growth factor binding proteins (IGFBP). This observation led to the hypothesis that neuroparsins might interact with endogenous insulin-related peptides. The present paper gives an overview of several neuroparsin family members that have hitherto been described in insects, as well as of a number of newly identified neuroparsin precursors from other species.

No abstract

This study describes the identification and distribution of two novel neuroparsin precursor transcripts (Scg-NPP3/Scg-NPP4) in the desert locust, Schistocerca gregaria. Unlike Scg-NPP1 and Scg-NPP2, both transcripts were not only detected in the brain, but also in various other tissues, such as fat body, ventral nerve cord, testis and male accessory glands. Northern analysis showed that the levels of these transcripts are regulated during larval development, as well as during moulting and reproductive cycles. A significant increase in both mRNAs was observed during the period that just precedes the initial sexual activity of adult females and males. In silico analysis of sequence databases revealed the existence of several other neuroparsin-like peptides in a variety of arthropod species, including crustaceans and chelicerates. Neuroparsins also display similarities with vertebrate IGFBP.