Evolutionarily conserved TRH neuropeptide pathway regulates growth in Caenorhabditis elegans

Abstract

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...

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

“…This include neuropeptide S (NPS) and crustacean cardioactive peptide (CCAP), orexin and allatotropin, neuropeptide FF/gonadotropin-inhibitory hormone (GnIH) and SIFamide galanin and allatostatin-A (Ast-A), as well as a link between vertebrate endothelin/gastrin-releasing peptide/neuromedin-B peptides and protostomian CCHamide/elevenin/GGNG peptides. Similar in silico analyses combined with receptor characterization studies in recent years have now increased the number of this core-set of bilaterian neuropeptides [36,57,62,66,139]. Thus, the origins of as many as 30 neuropeptide genes/families can now be traced back to Urbilateria as orthologs of several vertebrate neuropeptide signaling systems have been identified in insects and other protostomes ( Fig.…”

“…As more insect genomes and transcriptomes were sequenced [31,42,83,190,194] it became apparent that Drosophila has one of the smallest insect neuropeptidomes owing to the fact that it has lost several neuropeptide signaling systems which are present in basal insects like the migratory locust Locusta migratoria and the termite Zootermopsis nevadensis [31]. Neuropeptide systems lost in Drosophila include AKH/corazonin related peptide (ACP) [195], agatoxin-like peptide (ALP) [196], allatostatin-CCC [197], allatotropin [37], calcitonin, elevenin, neuroparsin, SMYamide [31], thyrotropin-releasing hormone (TRH) [66], tryptopyrokinin [198], neuroparsins [199] and inotocin (related to vertebrate oxytocin/vasopressin) [159]. The lack of powerful genetic tools in other insect models has hampered investigations into these signaling systems.…”

“…At first, the massive amount of new information mined from sequence databases was daunting, but with the rapid development of powerful genetic and imaging tools much experimental progress has been made to increase the understanding of the multiple functions of neuropeptides, especially in the worm Caenorhabditis elegans [see [39,[47][48][49][50][51][52][53][54][55][56]] and the fly Drosophila melanogaster (as will be discussed in this review) and more recently, in the marine annelid Platynereis dumerilii [57][58][59][60][61]. It is generally accepted that many of the genes encoding neuropeptides and peptide receptors in insects and other invertebrates are ancestrally related to those found in mammals [32,33,44,57,62], and recent work has suggested that in quite a few cases functions of peptidergic signaling are also partly conserved over evolution [19,23,[63][64][65][66]. Thus, invertebrates with their less complex neuronal and endocrine systems are being explored as models of neuropeptide signaling in a variety of functions [reviewed in [1, 2, 5-7, 9, 10, 30, 31, 43, 46, 67-74]].…”

New techniques, applications and perspectives in neuropeptide research

“…Beyond introducing a neuropeptide or a neuropeptide antagonist, neuropeptide production can be altered at the genetic level in organisms, such as mice, through the production of knockout or transgenic animals, or through targeted genome editing approaches (e.g. the CRISPR/Cas system) (Hay et al, 2017;Shao et al, 2016;Van Sinay et al, 2017). CRISPR/Cas has gained a lot of popularity for its speed, ease of use and efficiency compared to other methods used to knockout genes or create transgenic animals (Hay et al, 2017).…”

Royalactin induces copious longevity via increased translation and proteasome activity in C. elegans

“…Body size of WT adults was quantified analogous to refs. 73 Worm volumes were approximated using the cylinder volume formula: V = πL(W/2) 2 .…”