At the Transition from Invertebrates to Vertebrates, a Novel GnRH-Like Peptide Emerges in Amphioxus

Abstract

Gonadotropin-releasing hormone (GnRH) is a critical reproductive regulator in vertebrates. Homologous peptides are also found in invertebrates, with a variety of characterized functions. In the amphioxus, an invertebrate that provides the best model for the transition to vertebrates, four GnRH receptors (GnRHRs) were previously described, but their native ligands were not identified. Using a more sensitive search methodology with hidden Markov models, we identified the first GnRH-like peptide confirmed in the amphioxus Branchiostoma floridae. This peptide specifically activated one of the four GnRHRs. Although the primary structure of this peptide was divergent from any previously isolated GnRH peptide, the minimal conserved residues found in all other GnRH superfamily members were retained. The peptide was immunolocalized in proximity of the central canal of the anterior nerve cord, a region where other neuropeptides and receptors have been found. Additionally, the amphioxus GnRH-like gene was positioned in a locus surrounded by syntenic homologs of the human GnRH paralogon. The amphioxus GnRH-like peptide, with its distinct primary structure, activated a receptor with equal potency to multiple ligands that span the GnRH superfamily.

Phylogenetic analysis of phenotypic characters of Tunicata supports basal Appendicularia and monophyletic Ascidiacea

“…A neural gland is present in nearly all investigated species, except thaliacean species (Braun and Stach, ). Based on the similar position of Hatschek's pit and groove as well as the presence of gonadotropin hormones and the indication that gonadotropin‐releasing hormones are found in neural fibres close to Hatschek's pit, Hatschek's pit are coded in Cephalochordata as homologous to the neural gland and dorsal tubercle in tunicates (Stach, ; Gorbman, ; Roch et al., ). For Petromyzontidae the neural gland is homologized with the adenohypophysis, based on similarities of development, position and function (Romer and Parsons, ; Gorbman, , ; Kah et al., ). Position of neural gland compared to brain: (0) not ventral; (1) ventral.…”

The significance of Ciona intestinalis as a stem organism in integrative studies of functional evolution of the chordate endocrine, neuroendocrine, and nervous systems

“…a, C-terminal amidated; GnRH, gonadotropin releasing hormone; TK, tachykinin; NTLP, neurotensin-like peptide; OT/VP, oxytocin/vasopressin; CCK, cholecystokinin; +++, potent; ++, relatively potent; +, weak; N.D., not determined as well as the molecular and functional diversity among animal species (Millar et al, 2004;Millar, 2005;Kanda et al, 2006;Kah et al, 2007;Tello and Sherwood, 2009;Kawada et al, 2013;Roch et al, 2014). In C. intestinalis, six authentic GnRH peptides (t-GnRH-3 to -8), one structurally related peptide (Ci-GnRH-X), and four GnRH receptors (Ci-GnRH-R1 to -R4) have so far been identified (Adams et al, 2003;Kusakabe et al, 2003;Tello et al, 2005;Kawada et al, 2009a; Table 1).…”

Vertebrate Cranial Placodes as Evolutionary Innovations—The Ancestor's Tale

“…For example, gonadotropins were initially reported to be present in amphioxus based on such immunohistochemical studies (e.g., Nozaki & Gorbman, 1992) but were recently shown to be absent from the amphioxus genome like all other adenohypophyseal hormones Putnam et al, 2008). One GnRH peptide previously isolated from amphioxus (Chambery, Parente, Topo, Garcia-Fernandez, & D'Aniello, 2009) could not be confirmed in genomic analyses, but in contrast, another GnRH-like peptide has recently been identified in the amphioxus genome (Roch, Tello, & Sherwood, 2014). Since this peptide activates only one out of four GnRH receptors, additional GnRH peptides are probably present in amphioxus but remain to be identified.…”