Glucagon-like peptide (GCGL) is a novel potential TSH-releasing factor (TRF) in Chickens: I) Evidence for its potent and specific action on stimulating TSH mRNA expression and secretion in the pituitary

Evidence for Neuropeptide W Acting as a Physiological Corticotropin-releasing Inhibitory Factor in Male Chickens

In vertebrates, adrenocorticotropin (ACTH), released by the pituitary gland, is a critical part of the stress axis and stress response. Generally, the biosynthesis and secretion of ACTH are controlled by both hypothalamic stimulatory factors and inhibitory factors [eg, ACTH-releasing inhibitory factor (CRIF)], but the identity of this CRIF remains unrevealed. We characterized the neuropeptide B (NPB)/neuropeptide W (NPW) system in chickens and found that NPW could directly target the pituitary to inhibit growth hormone (GH) and prolactin (PRL) secretion via neuropeptide B/W receptor 2 (NPBWR2), which is completely different from the mechanism in mammals. The present study first carried out a series of assays to investigate the possibility that NPW acts as a physiological CRIF in chickens. The results showed that (1) NPW could inhibit ACTH synthesis and secretion by inhibiting the 3',5'-cyclic adenosine 5'-monophosphate/protein kinase A signaling cascade in vitro and in vivo; (2) NPBWR2 was expressed abundantly in corticotrophs (ACTH-producing cells), which are located mainly in cephalic lobe of chicken pituitary, as demonstrated by single-cell RNA-sequencing, immunofluorescent staining, and fluorescence in situ hybridization; (3) dexamethasone could stimulate pituitary NPBWR2 and hypothalamic NPW expression in chicks, which was accompanied by the decease of POMC messenger RNA levels, as revealed by in vitro and subcutaneous injection assays; and (4) the temporal expression profiles of NPW-NPBWR2 pair in hypothalamus-pituitary axis and POMC in pituitary were almost unanimous in chicken. Collectively, these findings provide comprehensive evidence for the first time that NPW is a potent physiological CRIF in chickens that plays a core role in suppressing the activity of the stress axis.

Identification of Key Candidate Genes in Runs of Homozygosity of the Genome of Two Chicken Breeds, Associated with Cold Adaptation

Simple Summary

The search for genomic regions related to adaptive abilities preserved in the chicken gene pool of two breeds, which have not been under intensive selection pressure, is of great importance for breeding in the future. This study aimed to identify key candidate genes associated with the adaptation of chickens to cold environments (using the example of the Russian White breed) by using molecular genetic methods. A total of 12 key genes on breed-specific ROH (runs of homozygosity) islands were identified, which may be potential candidate genes associated with the high level of adaptability of chickens to cold environments in the early postnatal period. These genes were associated with lipid metabolism, maintaining body temperature in cold environments, non-shivering thermogenesis and muscle development and are perspectives for further research.

Abstract

It is well known that the chicken gene pools have high adaptive abilities, including adaptation to cold environments. This research aimed to study the genomic distribution of runs of homozygosity (ROH) in a population of Russian White (RW) chickens as a result of selection for adaptation to cold environments in the early postnatal period, to perform a structural annotation of the discovered breed-specific regions of the genome (compared to chickens of the Amroks breed) and to suggest key candidate genes associated with the adaptation of RW chickens to cold environments. Genotyping of individual samples was performed using Illumina Chicken 60K SNP BeadChip^® chips. The search for homozygous regions by individual chromosomes was carried out using the PLINK 1.9 program and the detectRuns R package. Twelve key genes on breed-specific ROH islands were identified. They may be considered as potential candidate genes associated with the high adaptive ability of chickens in cold environments in the early postnatal period. Genes associated with lipid metabolism (SOCS3, NDUFA4, TXNRD2, IGFBP 1, IGFBP 3), maintaining body temperature in cold environments (ADIPOQ, GCGR, TRPM2), non-shivering thermogenesis (RYR2, CAMK2G, STK25) and muscle development (METTL21C) are perspectives for further research. This study contributes to our understanding of the mechanisms of adaptation to cold environments in chickens and provides a molecular basis for selection work.

Single-Cell RNA Sequencing Analysis of Chicken Anterior Pituitary: A Bird's-Eye View on Vertebrate Pituitary

It is well-established that anterior pituitary contains multiple endocrine cell populations, and each of them can secrete one/two hormone(s) to regulate vital physiological processes of vertebrates. However, the gene expression profiles of each pituitary cell population remains poorly characterized in most vertebrate groups. Here we analyzed the transcriptome of each cell population in adult chicken anterior pituitaries using single-cell RNA sequencing technology. The results showed that: (1) four out of five known endocrine cell clusters have been identified and designated as the lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs, respectively. Somatotrophs were not analyzed in the current study. Each cell cluster can express at least one known endocrine hormone, and novel marker genes (e.g., CD24 and HSPB1 in lactotrophs, NPBWR2 and NDRG1 in corticotrophs; DIO2 and SOUL in thyrotrophs, C5H11ORF96 and HPGDS in gonadotrophs) are identified. Interestingly, gonadotrophs were shown to abundantly express five peptide hormones: FSH, LH, GRP, CART and RLN3; (2) four non-endocrine/secretory cell types, including endothelial cells (expressing IGFBP7 and CFD) and folliculo-stellate cells (FS-cells, expressing S100A6 and S100A10), were identified in chicken anterior pituitaries. Among them, FS-cells can express many growth factors, peptides (e.g., WNT5A, HBEGF, Activins, VEGFC, NPY, and BMP4), and progenitor/stem cell-associated genes (e.g., Notch signaling components, CDH1), implying that the FS-cell cluster may act as a paracrine/autocrine signaling center and enrich pituitary progenitor/stem cells; (3) sexually dimorphic expression of many genes were identified in most cell clusters, including gonadotrophs and lactotrophs. Taken together, our data provides a bird's-eye view on the diverse aspects of anterior pituitaries, including cell composition, heterogeneity, cell-to-cell communication, and gene expression profiles, which facilitates our comprehensive understanding of vertebrate pituitary biology.

Evolution of thyrotropin-releasing factor extracellular communication units

Thyroid hormones (THs) are ancient signaling molecules that contribute to the regulation of metabolism, energy homeostasis and growth. In vertebrates, the hypothalamus-pituitary-thyroid (HPT) axis links the corresponding organs through hormonal signals, including thyrotropin releasing factor (TRF), and thyroid stimulating hormone (TSH) that ultimately activates the synthesis and secretion of THs from the thyroid gland. Although this axis is conserved among most vertebrates, the identity of the hypothalamic TRF that positively regulates TSH synthesis and secretion varies. We review the evolution of the hypothalamic factors that induce TSH secretion, including thyrotropin-releasing hormone (TRH), corticotrophin-releasing hormone (CRH), urotensin-1-3, and sauvagine, and non-mammalian glucagon-like peptide in metazoans. Each of these peptides is part of an extracellular communication unit likely composed of at least 3 elements: the peptide, G-protein coupled receptor and bioavailability regulator, set up on the central neuroendocrine articulation. The bioavailability regulators include a TRH-specific ecto-peptidase, pyroglutamyl peptidase II, and a CRH-binding protein, that together with peptide secretion/transport rate and transduction coupling and efficiency at receptor level shape TRF signal intensity and duration. These vertebrate TRF communication units were coopted from bilaterian ancestors. The bona fide elements appeared early in chordates, and are either used alternatively, in parallel, or sequentially, in different vertebrate classes to control centrally the activity of the HPT axis. Available data also suggest coincidence between apparition of ligand and bioavailability regulator.

Molecular evolution of GIP and Exendin and their receptors

Glucose-dependent insulinotropic polypeptide (GIP) is a product of the Gip gene and acts as an incretin hormone in mammals. Gip is most closely related to the proglucagon (Gcg) and Exendin genes and diverged from these very early in vertebrate evolution. In mammals, GIP acts through its specific receptor, encoded by the Gipr gene, which belongs to a subfamily of 7-transmembrane G-protein coupled receptor (GPCR) genes that also includes those for the proglucagon-derived peptides (Gcgr, Glp1r, and Glp2r), and the receptor for Exendin (Grlr). Gip, Gipr, Exendin, and Grlr genes are found in species from most vertebrate classes. While most species that have a Gip gene also have a Gipr gene, two classes of vertebrates, cartilaginous fish and birds, retain conserved Gip genes but lack Gipr genes. This raises the possibility the GIP signals through other receptors in some vertebrates. Exendin genes and the gene for its receptor, Grlr, are also found in diverse vertebrates, with the notable exception of mammals. Both GIP and Exendin likely have important roles in vertebrate physiology, but their roles are either dispensable or can be replaced by other hormones.

Characterization of a novel thyrotropin-releasing hormone receptor, TRHR3, in chickens

The physiological roles of thyrotropin-releasing hormone (TRH) are proposed to be mediated by TRH receptors (TRHR), which have been divided into 3 subtypes, namely, TRHR1, TRHR2, and TRHR3, in vertebrates. Although 2 TRH receptors (TRHR1 and TRHR3) have been predicted to exist in birds, it remains unclear whether TRHR3 is a functional TRH receptor similar to TRHR1. Here, we reported the functionality and tissue expression of TRHR3 in chickens. The cloned chicken TRHR3 (cTRHR3) encodes a receptor of 387 amino acids, which shares high-amino-acid identities (63–80%) to TRHR3 of parrots, lizards, Xenopus tropicalis, and tilapia and comparatively lower sequence identities to chicken TRHR1 or mouse TRHR2. Using cell-based luciferase reporter assays and Western blot, we demonstrated that similar to chicken TRHR1 (cTRHR1), cTRHR3 expressed in HEK 293 cells can be potently activated by TRH and that its activation stimulates multiple signaling pathways, indicating both TRH receptors are functional. Quantitative real-time PCR revealed that cTRHR1 and cTRHR3 are widely, but differentially, expressed in chicken tissues, and their expression is likely controlled by promoters located upstream of exon 1, which display strong promoter activities in cultured DF-1 cells. cTRHR1 is highly expressed in the anterior pituitary and testes, while cTRHR3 is highly expressed in the muscle, testes, fat, pituitary, spinal cord, and many brain regions (including hypothalamus). These findings indicate that TRH actions are likely mediated by 2 TRH receptors in chickens. In conclusion, our data provide the first piece of evidence that both cTRHR3 and cTRHR1 are functional TRH receptors, which helps to elucidate the physiological roles of TRH in birds.

Arginine vasotocin (AVT)/mesotocin (MT) receptors in chickens: Evidence for the possible involvement of AVT-AVPR1 signaling in the regulation of oviposition and pituitary prolactin expression

Two structurally related peptides, arginine vasotocin (AVT) and mesotocin (MT), are reported to regulate many physiological processes, such as anti-diuresis and oviposition in birds, and their actions are likely mediated by four AVT/MT receptors (AVPR1A, AVPR1B, MTR and AVPR2b), which are orthologous/paralogous to human AVPR1A, AVPR1B, OXTR and AVPR2 respectively. However, our knowledge regarding the functions of these avian AVT/MT receptors has been limited. Here, we examined the functionality and expression of these receptors in chickens and investigated the roles of AVT in the anterior pituitary. Our results showed that 1) AVPR1A, AVPR1B and AVPR2b could be preferentially activated by AVT, monitored by cell-based luciferase reporter assays and/or Western blot, indicating that they are AVT-specific receptors (AVPR1A; AVPR1B) or AVT-preferring receptor (AVPR2b) functionally coupled to intracellular calcium, MAPK/ERK and cAMP/PKA signaling pathways. In contrast, MTR could be activated by AVT and MT with similar potencies, indicating that MTR is a receptor common for both peptides; 2) Using qPCR, differential expression of the four receptors was found in chicken tissues including the oviduct and anterior pituitary. In particular, only AVPR1A is abundantly expressed in the uterus, suggesting its involvement in mediating AVT-induced oviposition. 3) In cultured chick pituitary cells, AVT could stimulate ACTH and PRL expression and secretion, an action likely mediated by AVPR1B and/or AVPR1A abundantly expressed in anterior pituitary. Collectively, our data helps to elucidate the roles of AVT/MT in birds, such as the 'oxytocic action' of AVT, which induces uterine muscle contraction during oviposition.

Regulation of Pituitary Cocaine- and Amphetamine-Regulated Transcript Expression and Secretion by Hypothalamic Gonadotropin-Releasing Hormone in Chickens

There is increasing evidence that cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the anterior pituitary of birds and mammals, suggesting that CART peptide may be a novel pituitary hormone and its expression and secretion is likely controlled by the hypothalamic factor(s). To substantiate this hypothesis, using chicken as an animal model, we examined the effects of gonadotropin-releasing hormone (GnRH) on pituitary CART secretion and expression and investigated whether GnRH could modulate plasma CART levels. The results showed that: (1) chicken GnRH (GnRH1 and GnRH2) could potently stimulate CART peptide secretion in intact pituitaries incubated in vitro, as detected by Western blot; (2) GnRH could also stimulate CART mRNA expression in cultured pituitary cells, as revealed by quantitative real-time polymerase chain reaction (qPCR) assay; (3) GnRH actions on pituitary CART expression and secretion are likely mediated by GnRH receptor coupled to the intracellular Ca²⁺, MEK/ERK, and cAMP/PKA signaling pathways; and (4) plasma CART levels are high in chickens at various developmental stages (1.2–3.5 ng/ml) and show an increasing trend towards sexual maturity, as detected by enzyme-linked immunosorbent assay (ELISA). Moreover, plasma CART levels could be significantly induced by intraperitoneal administration of GnRH in chicks. Taken together, our data provide the first collective evidence that CART peptide is a novel pituitary hormone and its expression and secretion are tightly controlled by hypothalamic GnRH, thus likely being an active player in the hypothalamic-pituitary-gonadal (HPG) axis.

Activation of GLP-1 and Glucagon Receptors Regulates Bile Homeostasis Independent of Thyroid Hormone

BACKGROUND

Balanced coagonists of glucagon-like peptide-1 (GLP-1) and glucagon receptors are emerging therapies for the treatment of obesity and diabetes. Such coagonists also regulate lipid metabolism, independent of their body weight lowering effects. Many actions of the coagonists are partly mediated by fibroblast growth factor 21 (FGF21) signaling, with the major exception of bile homeostasis. Since thyroid hormone is an important regulator of bile homeostasis, we studied the involvement of thyroid hormone in coagonist-induced changes in lipid and bile metabolism.

METHODS

We evaluated the effect of a single dose of coagonist Aib2 C24 chimera2 at 150 to 10000 µg/kg on tetraiodothyronine (T4) and triiodothyronine (T3) in high-fat diet-induced obese (DIO) mice and chow-fed mice. Repeated dose treatment of coagonist (150 µg/kg, subcutaneously) was assessed in four mice models namely, on lipid and bile homeostasis in DIO mice, propylthiouracil (PTU)-treated DIO mice, methimazole (MTM)-treated DIO mice and choline-deficient, L-amino acid-defined, highfat diet (CDAHFD)-induced nonalcoholic steatohepatitis (NASH).

RESULTS

Single dose treatment of coagonist did not alter serum T3 and T4 in chow-fed mice and DIO mice. Coagonist treatment improved lipid metabolism and biliary cholesterol excretion. Chronic treatment of GLP-1 and glucagon coagonist did not alter serum T3 in hypothyroid DIO mice and CDAHFDinduced NASH. Coagonist increased serum T4 in DIO mice after 4 and 40 weeks of treatment, though no change in T4 levels was observed in hypothyroid mice or mice with NASH.

CONCLUSION

Our data demonstrate that coagonist of GLP-1 and glucagon receptors does not modulate bile homeostasis via thyroid signaling.

Identification of a Novel Functional Corticotropin-Releasing Hormone (CRH2) in Chickens and Its Roles in Stimulating Pituitary TSHβ Expression and ACTH Secretion

Corticotropin-releasing hormone (CRH), together with its structurally and functionally related neuropeptides, constitute the CRH family and play critical roles in multiple physiological processes. Recently, a novel member of this family, namely CRH2, was identified in vertebrates, however, its functionality and physiological roles remain an open question. In this study, using chicken (c-) as the animal model, we characterized the expression and functionality of CRH2 and investigated its roles in anterior pituitary. Our results showed that (1) cCRH2 cDNA is predicted to encode a 40-aa mature peptide, which shares a higher amino acid sequence identity to cCRH (63%) than to other CRH family peptides (23-38%); (2) Using pGL3-CRE-luciferase reporter system, we demonstrated that cCRH2 is ~15 fold more potent in activating cCRH receptor 2 (CRHR2) than cCRHR1 when expressed in CHO cells, indicating that cCRH2 is bioactive and its action is mainly mediated by CRHR2; (3) Quantitative real-time PCR revealed that cCRH2 is widely expressed in chicken tissues including the hypothalamus and anterior pituitary, and its transcription is likely controlled by promoters near exon 1, which display strong promoter activity in cultured DF-1 and HEK293 cells; (4) In cultured chick pituitary cells, cCRH2 potently stimulates TSHβ expression and shows a lower potency in inducing ACTH secretion, indicating that pituitary/hypothalamic CRH2 can regulate pituitary functions. Collectively, our data provides the first piece of evidence to suggest that CRH2 play roles similar, but non-identical, to those of CRH, such as its differential actions on pituitary, and this helps to elucidate the roles of CRH2 in vertebrates.

Forever young: Endocrinology of paedomorphosis in the Mexican axolotl (Ambystoma mexicanum)

The Mexican axolotl (Ambystoma mexicanum) is a salamander species that does not undergo metamorphosis, resulting in the retention of juvenile characteristics in the mature breeding stage (paedomorphosis). Here we review the endocrinological studies investigating the proximate cause of axolotl paedomorphosis with a focus on the hypothalamo-pituitary-thyroid (HPT) axis. It is well established that axolotl paedomorphosis is a consequence of low activity of the HPT axis. The pituitary hormone thyrotropin (TSH) is capable of inducing metamorphosis in the axolotl, which indicates that all processes and interactions in the HPT axis below the pituitary level are functional, but that TSH release is impaired. In metamorphosing species, TSH secretion is largely controlled by the hypothalamic neuropeptide corticotropin-releasing hormone (CRH), which seems to have lost its thyrotropic activity in the axolotl. However, preliminary experiments have not yet confirmed a role for faulty CRH signalling in axolotl paedomorphosis. Other hypothalamic factors and potential pituitary inhibitors need to be investigated to identify their roles in amphibian metamorphosis and axolotl paedomorphosis.

Thyrotropic activity of corticotropin-releasing hormone in an altricial bird species, the zebra finch (Taeniopygia guttata)

In chicken, corticotropin-releasing hormone (CRH) acts as a thyrotropin (TSH)-releasing factor, mediated by the type 2 CRH receptor (CRHR2) on the thyrotropes of the pituitary gland. It is not known whether CRH also controls TSH release in non-precocial avian species that have a different pattern of thyroidal activity during their life cycle. Therefore, we investigated the TSH-releasing capacity of CRH in an altricial species, the zebra finch (Taeniopygia guttata). Cellular localisation of type 1 CRH receptor (CRHR1) and CRHR2 mRNA in the pituitary was determined by in situ hybridisation, combined with immunohistochemical staining of pituitary thyrotropes. In addition, isolated pituitary glands were stimulated with CRH to determine the effect on TSH release. Lastly, the mRNA levels of hormones and receptors involved in the control of thyroidal and adrenal function were measured by qPCR in zebra finch chicks between hatching and fledging, and in adults. Most of the hypophyseal CRHR2 mRNA co-localised with thyrotropes, whereas CRHR1 mRNA was found inbetween thyrotropes. Pituitary glands stimulated in vitro with CRH showed increased secretion of TSH-like activity. Pituitary CRHR2 mRNA expression decreased while pituitary TSHB mRNA and brain CRH mRNA levels increased towards fledging, similar as seen in chicken hatching. These results suggest that CRHR2 expressed on thyrotropes is likely mediating CRH-induced TSH release in altricial avian species like it does in precocial species, and that the increased thyroid hormone levels towards fledging in altricial birds are the result of increased hypothalamic stimulation, in which the thyrotropic activity of CRH may initially play a role.

Characterization of the Apelin/Elabela Receptors (APLNR) in Chickens, Turtles, and Zebrafish: Identification of a Novel Apelin-Specific Receptor in Teleosts

Apelin receptor(s) (APLNR) are suggested to mediate the actions of apelin and Elabela (ELA) peptides in many physiological processes, including cardiovascular development and food intake in vertebrates. However, the functionality of APLNR has not been examined in most vertebrate groups. Here, we characterized two APLNRs APLNR1, APLNR2) in chickens and red-eared sliders, and three APLNRs in zebrafish (APLNR2a, APLNR2b, APLNR3a), which are homologous to human APLNR. Using luciferase-reporter assays or Western blot, we demonstrated that in chickens, APLNR1 (not APLNR2) expressed in HEK293 cells was potently activated by chicken apelin-36 and ELA-32 and coupled to Gi-cAMP and MAPK/ERK signaling pathways, indicating a crucial role of APLNR1 in mediating apelin/ELA actions; in red-eared sliders, APLNR2 (not APLNR1) was potently activated by apelin-36/ELA-32, suggesting that APLNR2 may mediate apelin/ELA actions; in zebrafish, both APLNR2a and APLNR2b were potently activated by apelin-36/ELA-32 and coupled to Gi-cAMP signaling pathway, as previously proposed, whereas the novel APLNR3a was specifically and potently activated by apelin. Similarly, an apelin-specific receptor (APLNR3b) sharing 57% sequence identity with zebrafish APLNR3a was identified in Nile tilapia. Collectively, our data facilitates the uncovering of the roles of APLNR signaling in different vertebrate groups and suggests a key functional switch between APLNR1 and APLNR2/3 in mediating the actions of ELA and apelin during vertebrate evolution.

Characterization of NMB, GRP and their receptors (BRS3, NMBR and GRPR) in chickens

The two structurally and functionally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) play critical roles in many physiological/pathological processes in mammals. However, the information regarding the expression and functionality of avian NMB, GRP and their receptors is limited. Here, we characterized cNMB, cGRP and their receptors (cNMBR, cGRPR and cBRS3) in chickens. Our results showed that: (1) cNMBR and cGRPR expressed in CHO cells could be potently activated by cNMB and cGRP, respectively, as monitored by cell-based luciferase reporter assays, indicating that cNMBR and cGRPR are cNMB- and cGRP-specific receptors; strikingly, BRS3 of chickens (/spotted gars), which is orthologous to mouse bombesin receptor subtype-3 (BRS3), could be potently activated by GRP and NMB, demonstrating that both peptides are the endogenous ligands for chicken (/spotted gar) BRS3; (2) quantitative real-time PCR (qPCR) revealed that cGRPR is widely expressed in chicken tissues with abundant expression in the ovary, pancreas, proventriculus, spinal cord and brain, whereas cNMB, cNMBR and cBRS3 are mainly expressed in the brain and testes; (3) interestingly, qPCR, Western blot and immunostaining revealed that cGRP is predominantly expressed in the anterior pituitary and mainly localized to LH-cells, suggesting that cGRP is likely a novel pituitary hormone in chickens. In summary, our data help to uncover the roles of GRP, NMB and their receptors in birds, and provide the first persuasive evidence from an evolutionary prospective that in vertebrates, GRP and NMB are the endogenous ligands for BRS3, an orphan receptor that has puzzled endocrinologists for more than two decades.

Characterization of Neuropeptide B (NPB), Neuropeptide W (NPW), and Their Receptors in Chickens: Evidence for NPW Being a Novel Inhibitor of Pituitary GH and Prolactin Secretion

The 2 structurally and functionally related peptides, neuropeptide B (NPB) and neuropeptide W (NPW), together with their receptor(s) (NPBWR1/NPBWR2) constitute the NPB/NPW system, which acts mainly on the central nervous system to regulate many physiological processes in mammals. However, little is known about this NPB/NPW system in nonmammalian vertebrates. In this study, the functionality and expression of this NPB/NPW system and its actions on the pituitary were investigated in chickens. The results showed that: 1) chicken NPB/NPW system comprises an NPB peptide of 28 amino acids (cNPB28), an NPW peptide of 23 or 30 amino acids (cNPW23/cNPW30), and their 2 receptors (cNPBWR1 and cNPBWR2), which are highly homologous to their human counterparts. 2) Using a pGL3-CRE-luciferase reporter system, we demonstrated that cNPBWR2 expressed in Chinese hamster ovary cells can be potently activated by cNPW23 (not cNPB28), and its activation inhibits the intracellular cAMP signaling pathway, whereas cNPBWR1 shows no response to peptide treatment, suggesting a crucial role of cNPBWR2 in mediating cNPW/cNPB actions. 3) Quantitative real-time PCR revealed that cNPW and cNPB are widely expressed in chicken tissues, including hypothalamus, whereas cNPBWR1 and cNPBWR2 are mainly expressed in brain or pituitary. 4) In accordance with abundant cNPBWR2 expression in pituitary, cNPW23 could dose dependently inhibit GH and prolactin secretion induced by GHRH and vasoactive intestinal polypeptide, respectively, in cultured chick pituitary cells, as monitored by Western blotting. Collectively, our data reveal a functional NPB/NPW system in birds and offer the first proof that NPW can act directly on pituitary to inhibit GH/prolactin secretion in vertebrates.

Corticotropin-releasing hormone: Mediator of vertebrate life stage transitions?

Hormones, particularly thyroid hormones and corticosteroids, play critical roles in vertebrate life stage transitions such as amphibian metamorphosis, hatching in precocial birds, and smoltification in salmonids. Since they synergistically regulate several metabolic and developmental processes that accompany vertebrate life stage transitions, the existence of extensive cross-communication between the adrenal/interrenal and thyroidal axes is not surprising. Synergies of corticosteroids and thyroid hormones are based on effects at the level of tissue hormone sensitivity and gene regulation. In addition, in representative nonmammalian vertebrates, corticotropin-releasing hormone (CRH) stimulates hypophyseal thyrotropin secretion, and thus functions as a common regulator of both the adrenal/interrenal and thyroidal axes to release corticosteroids and thyroid hormones. The dual function of CRH has been speculated to control or affect the timing of vertebrate life history transitions across taxa. After a brief overview of recent insights in the molecular mechanisms behind the synergic actions of thyroid hormones and corticosteroids during life stage transitions, this review examines the evidence for a possible role of CRH in controlling vertebrate life stage transitions.

Corticotropin-releasing hormone (CRH) stimulates cocaine- and amphetamine-regulated transcript gene (CART1) expression through CRH type 1 receptor (CRHR1) in chicken anterior pituitary

Cocaine- and amphetamine-regulated transcript (CART) peptide(s) is generally viewed as neuropeptide(s) and can control food intake in vertebrates, however, our recent study revealed that CART1 peptide is predominantly expressed in chicken anterior pituitary, suggesting that cCART1 peptide is a novel pituitary hormone in chickens and its expression is likely controlled by hypothalamic factor(s). To test this hypothesis, in this study, we examined the spatial expression of CART1 in chicken anterior pituitary and investigated the effect of hypothalamic corticotropin-releasing hormone (CRH) on pituitary cCART1 expression. The results showed that: 1) CART1 is expressed in both caudal and cephalic lobes of chicken anterior pituitary, revealed by quantitative real-time PCR (qPCR), western blot and immuno-histochemical staining; 2) CRH potently stimulates cCART1 mRNA expression in cultured chick pituitary cells, as examined by qPCR, and this effect is blocked by CP154526 (and not K41498), an antagonist specific for chicken CRH type I receptor (cCRHR1), suggesting that cCRHR1 expressed on corticotrophs mediates this action; 3) the stimulatory effect of CRH on pituitary cCART1 expression is inhibited by pharmacological drugs targeting the intracellular AC/cAMP/PKA, PLC/IP3/Ca(2+), and MEK/ERK signaling pathways. This finding, together with the functional coupling of these signaling pathways to cCRHR1 expressed in CHO cells demonstrated by luciferase reporter assay systems, indicates that these intracellular signaling pathways coupled to cCRHR1 can mediate CRH action. Collectively, our present study offers the first substantial evidence that hypothalamic CRH can stimulate pituitary CART1 expression via activation of CRHR1 in a vertebrate species.

Extra-pituitary prolactin (PRL) and prolactin-like protein (PRL-L) in chickens and zebrafish

It is generally believed that in vertebrates, prolactin (PRL) is predominantly synthesized and released by pituitary lactotrophs and plays important roles in many physiological processes via activation of PRL receptor (PRLR), including water and electrolyte balance, reproduction, growth and development, metabolism, immuno-modulation, and behavior. However, there is increasing evidence showing that PRL and the newly identified 'prolactin-like protein (PRL-L)', a novel ligand of PRL receptor, are also expressed in a variety of extra-pituitary tissues, such as the brain, skin, ovary, and testes in non-mammalian vertebrates. In this brief review, we summarize the recent research progress on the structure, biological activities, and extra-pituitary expression of PRL and PRL-L in chickens (Gallus gallus) and zebrafish (Danio rerio) from our and other laboratories and briefly discuss their potential paracrine/autocrine roles in non-mammalian vertebrates, which may promote us to rethink the broad spectrum of PRL actions previously attributed to pituitary PRL only.

Characterization of the Two CART Genes (CART1 and CART2) in Chickens (Gallus gallus)

Cocaine- and amphetamine-regulated transcript (CART) peptide is implicated in the control of avian energy balance, however, the structure and expression of CART gene(s) remains largely unknown in birds. Here, we cloned and characterized two CART genes (named cCART1 and cCART2) in chickens. The cloned cCART1 is predicted to generate two bioactive peptides, cCART1(42-89) and cCART1(49-89), which share high amino acid sequence identity (94-98%) with their mammalian counterparts, while the novel cCART2 may produce a bioactive peptide cCART2(51-91) with 59% identity to cCART1. Interestingly, quantitative RT-PCR revealed that cCART1 is predominantly expressed in the anterior pituitary and less abundantly in the hypothalamus. In accordance with this finding, cCART1 peptide was easily detected in the anterior pituitary by Western blot, and its secretion from chick pituitaries incubated in vitro was enhanced by ionomycin and forskolin treatment, indicating that cCART1 is a novel peptide hormone produced by the anterior pituitary. Moreover, cCART1 mRNA expression in both the pituitary and hypothalamus is down-regulated by 48-h fasting, suggesting its expression is affected by energy status. Unlike cCART1, cCART2 is only weakly expressed in most tissues examined by RT-PCR, implying a less significant role of cCART2 in chickens. As in chickens, 2 or more CART genes, likely generated by gene and genome duplication event(s), were also identified in other non-mammalian vertebrate species including coelacanth. Collectively, the identification and characterization of CART genes in birds helps to uncover the roles of CART peptide(s) in vertebrates and provides clues to the evolutionary history of vertebrate CART genes.