Background: To obtain reliable quantitative RT-PCR data, normalization relative to stable housekeeping genes is required. However, in practice, expression levels of 'typical' housekeeping genes have been found to vary between tissues and under different experimental conditions. To date, validation studies of reference genes in insects are extremely rare and have never been performed in locusts. In this study, putative housekeeping genes were identified in the desert locust, Schistocerca gregaria and two different software programs (geNorm and Normfinder) were applied to assess the stability of thesegenes.

Neuropeptides are by far the largest and most diverse group of signaling molecules in multicellular organisms. They are ancient molecules important in regulating a multitude of processes. Their small proteinaceous character allowed them to evolve and radiate quickly into numerous different molecules. On average, hundreds of distinct neuropeptides are present in animals, sometimes with unique classes that do not occur in distantly related species. Acting as neurotransmitters, neuromodulators, hormones, or growth factors, they are extremely diverse and are involved in controlling growth, development, ecdysis, digestion, diuresis, and many more physiological processes. Neuropeptides are also crucial in regulating myriad behavioral actions associated with feeding, courtship, sleep, learning and memory, stress, addiction, and social interactions. In general, behavior ensures that an organism can survive in its environment and is defined as any action that can change an organism's relationship to its surroundings. Even though the mode of action of neuropeptides in insects has been vigorously studied, relatively little is known about most neuropeptides and only a few model insects have been investigated. Here, we provide an overview of the roles neuropeptides play in insect behavior. We conclude that multiple neuropeptides need to work in concert to coordinate certain behaviors. Additionally, most neuropeptides studied to date have more than a single function.

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.

In vertebrates thyrotropin-releasing hormone (TRH) is a highly conserved neuropeptide that exerts the hormonal control of thyroidstimulating hormone (TSH) levels as well as neuromodulatory functions. However, a functional equivalent in protostomian animals remains unknown, although TRH receptors are conserved in proto-and deuterostomians. Here we identify a TRH-like neuropeptide precursor in Caenorhabditis elegans that belongs to a bilaterian family of TRH precursors. Using CRISPR/Cas9 and RNAi reverse genetics, we show that TRH-like neuropeptides, through the activation of their receptor TRHR-1, promote growth in C. elegans. TRH-like peptides from pharyngeal motor neurons are required for normal body size, and knockdown of their receptor in pharyngeal muscle cells reduces growth. Mutants deficient for TRH signaling have no defects in pharyngeal pumping or isthmus peristalsis rates, but their growth defect depends on the bacterial diet. In addition to the decrease in growth, trh-1 mutants have a reduced number of offspring. Our study suggests that TRH is an evolutionarily ancient neuropeptide, having its origin before the divergence of protostomes and deuterostomes, and may ancestrally have been involved in the control of postembryonic growth and reproduction.thyrotropin-releasing hormone | C. elegans | neuropeptide | molecular evolution | growth regulation A fter Harris's initial proposal on the hypothalamic control of pituitary secretion (1), it took almost two decades to identify the first hypophysiotropic molecule. In 1969 the groups of Schally and Guillemin isolated the tripeptide pQHP-NH 2 (2, 3), named "thyrotropin-releasing hormone" (TRH). The sequence of TRH is fully conserved across all vertebrates, indicating that strong evolutionary pressure has acted to preserve its structure (4). In all vertebrate phyla TRH is synthesized from a larger precursor protein (preproTRH) that contains five to eight copies of the TRH sequence (4). Following the explosion of genome and transcriptome sequence data, preproTRH was identified in chordate species lacking a bona fide pituitary, e.g., cephalochordates (5), and in the genomes of more ancient deuterostomes, including echinoderms (6, 7). In contrast to vertebrate (pQHP-NH 2 ) and chordate (pQSP-NH 2 ) tripeptide TRHs, most predicted echinoderm TRHs are tetrapeptidesLike vertebrate TRH, they are small peptides with an N-terminal pyroglutamate, a C-terminal amide (-NH 2 ) group, and amino acids with aromatic or cyclic side chains at the second and third positions. TRH therefore is widely distributed throughout the deuterostomian lineage of the Animal Kingdom, suggesting an ancient origin for this neuropeptide hormone.In mammals, hypothalamic TRH is the prime regulator of the set point of thyroid-stimulating hormone (TSH) synthesis and secretion by the anterior pituitary thyrotrophs (9). TSH secretion stimulates the thyroid gland to produce the thyroid hormones (THs) thyroxine (T 4 ) and triiodothyronine (T 3 ). The hypothalamus-pituitary-thyroid (HPT) axis is essentia...

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.