Spexin and a novel cichlid-specific spexin paralog both inhibit FSH and LH through a specific galanin receptor (Galr2b) in tilapia

Abstract

21Spexin (SPX) is a 14 amino acid peptide hormone that has pleiotropic functions 22 across vertebrates, one of which is involvement in the brain-pituitary-gonad axis of fish. 23 SPX(1) has been identified in each class of vertebrates, and a second SPX (named SPX2) 24 has been found in some non-mammalian species. We have cloned two spexin paralogs, 25 designated as Spx1a and Spx1b, from Nile tilapia (Oreochromis niloticus) that have 26 varying tissue distribution patterns. Spx1b is a novel peptide only identified in cichlid 27 fish, and is more closely related to Spx1 than Spx2 homologs as supported by 28 phylogenetic, synteny, and functional analyses. Kisspeptin, Spx, and galanin (Gal) 29 peptides and their corresponding kiss receptors and Gal receptors (Galrs), respectively, 30 are evolutionarily related. Cloning of six tilapia Galrs (Galr1a, Galr1b, Galr2a, Galr2b, 31 Galr type 1, and Galr type 2) and subsequent in vitro second-messenger reporter assays 32 for Gαs, Gαq, and Gαi suggests that Gal and Spx activate Galr1a/Galr2a and Galr2b, 33 respectively. A decrease in plasma follicle stimulating hormone and luteinizing hormone 34 concentrations was observed with injections of Spx1a or Spx1b in vivo. Additionally, 35 application of Spx1a to pituitary slices decreased the firing rate of LH cells, suggesting 36 direct inhibition at the pituitary level. These data collectively suggest an inhibitory 37 mechanism of action against the secretion of gonadotropins for a traditional and a novel 38 spexin paralog in cichlid species. 39 40 42 methods [1], and then also by chemical methods [2] in humans. These computational 43 methods have been attempted mostly on the basis of the characteristics of the 44 prohormones from which active neuropeptides are processed. The mature peptide 45 sequence contains 14 amino acids that are flanked by monobasic and dibasic proteolytic 46 cleavage sites. The mature spexin peptide was found to be identical in all tetrapods and 47 elephant shark, and differs in only one amino acid (A 13 T) in piscine species. A paralog of 48 spexin, termed Spx2, was later identified in non-mammalian species [3]. In mammals, 49 Spx was found to participate in inducing stomach contraction [1], inhibiting 50 adrenocortical cell proliferation[4], postnatal hypoxia response [5], cardiovascular and 51 renal modulation[6], nociceptive response [7], fatty acid absorption and weight regulation 52 [8], and diabetes [9]. In teleosts, functional studies of Spx1 mainly focused on its 53 inhibitory role in the regulation of reproduction [10] and food intake [2] [11]. However, a 54 recent study reported that spx1 knock-out zebrafish exhibited normal reproductive 55 capability but higher food intake than wild type fish, an effect mediated via increased 56 expression of the appetite stimulant, agouti-related peptide AgRP1 [12].57The galanergic neurotransmission system is one of the newest described signaling 58 systems. Today, the galanin family consists of galanin (Gal), galanin-like peptide (GalP), 59...

Structure and functions of spexin as a new neuroendocrine signal

“…However, in a study with grouper fishes, SPX treatment does not affect mRNA expression of LH and FSH in the pituitary (7). Contrary to this data, there are studies showing that SPX can inhibit LH and FSH secretion (9,20,22). In another study, the effect of SPX on gamete maturation and puberty onset was investigated, and it was reported that SPX knockout zebrafish has fertility without abnormality in the timing of pubertal onset or gamete maturation in the testes and ovary (55).…”

“…The widespread synthesis of SPX has pointed out that it regulates many physiological functions in the body. For instance, SPX affects food intake (6)(7)(8)(9)(10)25) glucose/fat metabolism (11)(12)(13)(14)(15) gastrointestinal motility (1,16), pain perception (5,17,18), endocrine (10,12,(19)(20)(21), reproductive (7,10,20,(22)(23)(24) and cardiovascular functions (17). Additionally, the important roles of SPX have been revealed in pathological conditions such as obesity, anorexia nervosa, diabetes, anxiety, and depression (26)(27)(28)(29)(30)(31).…”

Spexin in the European sea bass, Dicentrarchus labrax: Characterization, brain distribution, and interaction with Gnrh and Gnih neurons

“…The mature peptide sequence, NWTPQAMLYLKGAQ‐NH 2 , is flanked by RR/KR and GRR dibasic proteolytic cleavage sites, and it is identical in all tetrapods studied so far (Lv et al., 2019; Mirabeau et al., 2007; Sonmez et al., 2009), except in panda, dog, and cat with a substitution of Ala 6 to Ser 6 . In fish, Spx orthologs differ from mammalian and avian forms in only one amino acid, an Ala 13 to Thr 13 , a substitution that is present in all species investigated to date (Cohen et al., 2020; Lim et al., 2019; Ma et al., 2018). Recently, another paralogous form of Spx, called Spx2, has been identified in a few non‐mammalian species (D. K. Kim et al., 2014), and hence the initial mature Spx was termed Spx1.…”

“…Recently, another paralogous form of Spx, called Spx2, has been identified in a few non‐mammalian species (D. K. Kim et al., 2014), and hence the initial mature Spx was termed Spx1. It is worth mentioning that two Spx1 paralogs, designated as Spx1a and Spx1b, were found in Nile tilapia, while Spx2 is absent in this species (Cohen et al., 2020).…”

Identifying the Interaction of the Brain and the Pituitary in Social – and Reproductive – State of Tilapia by Transcriptome Analyses

“…While most of the significant factors along the HPG axis are conserved between mammals and teleost [4, 5], little is known about the mechanisms that regulate GnRH activity and its direct control on gonadotrophs. While various neuropeptides have been suggested to interact in the regulation of GtH secretion, such as kisspeptin [6, 7], neurokinin B and F [8, 9], GnIH [8], and spexin [10], how they interact with the different components of the HPG axis remains unknown. An additional important component of the HPG axis is the feedback regulation of sex steroids (testosterone [T] and estradiol [E 2 ]) on the brain and the pituitary.…”