1,721,245 research outputs found
The role of secretin in appetite control
No full textMultiple gut hormones are involved in the regulation of food intake. Secretin
(SCT), a classical gut hormone, is released into the circulation from the duodenal
S-cells when acidic chyme enters the duodenum and performs the major functions
of delaying gastric emptying, stimulating fluid secretion from pancreas and liver
to optimize the digestion process. In recent years, SCT and its receptor (SCTR)
have been identified in discrete nuclei of the hypothalamus, including the
paraventricular nucleus (PVN) and the arcuate nucleus (Arc). The occurrence of
SCT and SCTR in the brain regions that are engaged in regulating body energy
homeostasis and the release pattern of SCT after meals support a functional role of
SCT in appetite control. In this study, the effect of SCT on feeding behavior was
investigated using wild-type (wt), SCT?/?, and SCT receptor-deficient (SCTR?/?)
mice. We found that both central and peripheral administration of SCT could
reduce food intake in wt but not in SCTR?/?mice. SCT induce Fos expression in
the PVN and Arc, suggesting the activation of hypothalamic feeding centers by
this peptide. Consistent with this notion, SCT was found to increase
proopiomelanocortin (POMC), but reduce agouti-related protein (AgRP)
transcripts in the Arc, and augment thyrotropin-releasing hormone (TRH) and
melanocortin-4 receptor (MC4R) mRNA expression in the PVN. In addition,
pretreatment with SHU9119, an antagonist for MC4R, abolished the anorexia
induced by SCT, suggesting that SCT may inhibit food intake via a
melanocortin-dependent pathway. Gut hormones signals the brain to modulate the
feeding behavior via the vagal afferent nerve, bloodstream or both. Here we
showed that peripheral SCT-induced anorexia was attenuated in mice with
subdiaphragmatic vagotomy, capsaicin treatment and bilateral midbrain
transections. In summary, our data identify peripheral SCT as an anorectic peptide
exerting its action via the melanocortin system and the vagal afferent contributes a
major route in mediating the inhibitory effect of peripheral SCT on food intake.
The present findings advance our understanding of the role of gut hormones in the
regulation of appetite.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Molecular evolution of secretin/glucagon receptor superfamily in osteichthyans
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
The role of secretin in mediating the osmoregulatory functions of angiotensin II
No full textpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Secretin modulates the postnatal development of mouse cerebellar cortex via PKA- and ERK- dependent pathways
No full textThe role of secretin (SCT) and secretin receptor (SCTR) in behavioral control has been extensively studied. Without an intact SCT/SCTR axis, multiple neurobehavioral functions including motor coordination, motor learning, social behavior and cognitive behavior are impaired in different mouse models. The cerebellum has been well-established as the control center for motor coordination and motor learning while there is growing acceptance for its importance in cognition. Notably, normal cerebellar function depends on well-orchestrated processes during morphogenesis and development. In particular, the cerebellum exhibits dramatic morphological change and considerable weight increase during the postnatal period due to Purkinje cell dendritogenesis and granular cell proliferation and migration. Of equal importance, apoptosis acts as part of a “quality-control” to help provide precise postnatal development. Nevertheless, it remains unclear whether the SCT/SCTR axis is involved in regulating postnatal morphogenesis and development of the cerebellum, which has been implicated in the pathogenesis of psychiatric disorders. In the present study, the potential role of SCT in cerebellar development was explored at multiple postnatal stages. Both SCT and SCTR were found to be constitutively expressed in the postnatal cerebellum with their expression levels significantly and consistently upregulated at the earliest postnatal stages. The expression of SCT was observed almost exclusively in Purkinje cells, whereas high expression levels of SCTR were shown in several cerebellar cell types, including Purkinje cells and granular cells. Using SCT knockout (Sct-/-) mice and their wild-type littermates (Sct+/+), it was demonstrated that SCT deprivation resulted in various abnormal developmental phenotypes, including reduced Purkinje cell density, underdeveloped Purkinje cell dendritic arbors, premature granular cell migration, and increased apoptotic activity. Furthermore, the signaling pathways utilized by SCT to regulate apoptosis were characterized. In Sct-/- mice, the phosphorylation levels of ERK1/2 and its downstream effector p90RSK were significantly decreased, whereas phosphorylated Akt remained unchanged. SCT deprivation further reduced the expression of CREB and its downstream survival proteins bcl-2 and bcl-xl. On ex vivo cultured para-sagittal cerebellar sections harvested from Sct-/- mice, SCT treatment significantly stimulated ERK1/2, p90RSK and CREB phosphorylation and bcl-2 and bcl-xl expression in a dose-dependent manner. In contrast, caspase-3 activation was negatively correlated with SCT dosage. The addition of PKA inhibitor H89, and/or ERK1/2 inhibitor U0126, or p90RSK inhibitor BI-D1870 all remarkably abolished the anti-apoptotic effect of SCT, which could only be fully abolished by co-treatment with H89 and U0126. Moreover, ERK1/2 and its downstream effector p90RSK were partially suppressed in the presence H89. In a similar manner, CREB phosphorylation and expressions of bcl-2 and bcl-xl were restored by SCT, and this recovery was partially suppressed by H89 or U0126 but was fully suppressed when both drugs were combined. Taken together, these results clearly indicate the convergence of PKA and ERK signaling pathways toward the CREB survival pathway and caspase-3 apoptotic pathway. In summary, the results of this study illustrate that SCT, as a previously unrecognized participant, is required for normal cerebellar postnatal development, emphasizing the necessary role of SCT in cerebellar-related functions.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Cloning and characterization of the first amphibian secretins and secretin receptor: functional implication ofsecretin with orexin in amphibians
No full textpublished_or_final_versionBiological SciencesMasterMaster of Philosoph
Potential roles of primitive secretin-like and insulin-like peptides in embryogenesis of a cephalochordate, the amphioxus
No full textSecretin and insulin peptide families are two well-studied hormone families which have pleiotropic actions on both the digestive tract and the brain in vertebrate. Their involvements in vertebrate embryogenesis have been abundantly reported. Defects in these proteins will lead to various diseases such as sterility, diabetes, growth retardation. But it’s always hard to fully understand the physiological roles of these genes when researches are performed on complex systems of vertebrate. Amphioxus belongs to the cephalochordata lineage, it has a unique evolutionarily position where is at the transition of invertebrate to vertebrate, it keeps most features of the ancient vertebrates and the embryo development is much simpler. Thus, in this project, We use amphioxus as animal model, studying the molecular and functional evolution of secretin- and insulin-like peptides in embryogenesis, providing insights into some of the complex issues in vertebrate embryo development.
Amphioxus CRH-like peptides and receptors were identified in this study, functional analyses revealed that two of the cloned receptors (Bflo_CRHRa and Bbel_CRHRa) can be activated by amphioxus CRH peptide, demonstrating the existence of functional CRH peptide-receptor pair before the origin of vertebrates. By qRT‐PCR and immunofluorescence staining, it was found that CRH peptide and receptor possessed a similar distribution pattern with the highest expression level in the nerve cord. The characterization of CRH peptide-receptor pair means all five subfamilies of secretin-like GPCRs and peptides have been identified in amphioxus. Phylogenetic analysis placed amphioxus peptides/receptors at the base of the clade comprising vertebrate corresponding peptides/receptors, indicating that members in vertebrate secretin-like ligands and GPCR family were evolved from one pre-existing ancestral gene of Chordate.
Studies of amphioxus transcriptome data revealed that both secretin and insulin family peptides have high expression in neurula stage during embryogenesis. In order to understand their potential roles during different embryo development stages, whole mount in situ hybridization was performed to show the spatio-temporal expression pattern. All tested 8 secretin family peptides were expressed in the developing nerve cord while ILP and IGFBP had distinct expressions in the gut, implying important and different roles of these two peptide families in amphioxus embryogenesis.
Taking the advantage of biotechnology in generating amphioxus transgenic lines, seven amphioxus mutant lines have been generating including CTFP2, CRH, PACAP/Gluc-a, PACAP/GlucR, PTHR, ILP and IGFBP. Studies of ILP and IGFBP mutant lines were performed. We found IGFBP-/- amphioxus could survive to adulthood and no significant phenotypic change was detected during embryo development. ILP-/- amphioxus had severe growth retardation and could only reach two-gill-slit stage with less than one month’s life. Whole mount in situ hybridization study showed that ILP deficiency caused decreased expression of Pax1/9, Six1/2, Eya, Tbx1/10 in pharynx region and PTH2 in pre-oral pit in larva stage. No significant differences were detected for the checked anterior development markers. These results indicate that ILP is essential for amphioxus survival and it plays important roles in amphioxus embryogenesis especially in the gill development. And the involvement of insulin/IGF signaling in head and neural induction may be an innovation in vertebrate linage.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Class B GPCR ligands' expression patterns in developing amphioxus; their role embryogenesis and their evolutionary significance
No full textDue to its unique position in the evolutionary time scale at the interface of vertebrates and invertebrates Amphioxus, a cephalochordate in phylum chordate, has served as a model organism to study evolution for over a century. In our lab, we have previously reported the presence of an ortholog to Pituitary adenylate cyclase-activating peptide (PACAP), Glucagon, Parathyroid hormone (PTH) and their receptors in amphioxus. In this study, we analysed the expression pattern of class B guanine nucleotide-binding proteins (G protein)–coupled receptors (GPCRs) ligands which include Calcitonin-like, Corticotropin releasing hormone-like, PACAP-Glucagon-like and PTH-like peptides during the development of amphioxus embryo.
Taking advantage of the openly available transcriptome data from Branchiostoma floridae (Bf) and Branchiostoma Belcheri (Bb), two of the widely studied Amphioxus species; we explored the expression pattern and possible functions of class B ligands in the development of amphioxus. The differential expression across different developmental stages from un-fertilized egg through mature adult were analysed from the available data. We compared the expression pattern of the class B ligands across five other species; Danio rerio (Dr-zebrafish), Xenopus tropicalis (Xt- Western clawed frog), Pelodiscus sinensis (Ps-Chinese softshell turtle), Gallus gallus (Gg-Chicken) and Mus musculus (Mm-mouse). These data helped us to focus the study further on specific stages in development from early neurula through three gill-slit stage in amphioxus.
The hour-glass model of developmental evolution suggests that the constrains on evolution can induce stringency at the phylotypic stages (late neurula/early larvae) in amphioxus or early organogenesis in vertebrates. It is also important to note that the analysis on the transcriptomic data revealed that most class B GPCRs and ligands are expressed in these developmental stages. Although, there has been a constant debate on the hour-glass model, there is a general agreement that there are certain constrains like check-points in embryonic development which confer evolutionary stringency.
In this study, we hope to understand how conserved the expression patterns during embryonic development is for the various orthologs of known vertebrate class B members in amphioxus. We performed whole mount in-situ hybridization experiments on these set of genes from early neurula to three gill-slit stage larvae. The results might help in further understanding the neuroendocrine system which operates in basal chordates. With only about 20,000 neurons, amphioxus is also a useful tool in helping us to understand the development of the nervous system which is extremely complex among mammals.
Our investigation into the class B ligands revealed striking similarities in expression pattern in late neurula and larval stages with vertebrates. All the ligands’ transcripts were found to express in the late neurula and larval stages studied in the developing nerve cord. More interesting, when comparing the results with available information on vertebrate ortholog expression pattern, we identified similarities in the spaciotemporal expression of transcripts in PACAP-Glucagon subfamily in the developing embryo. This significant level of conservation in the expression pattern observed, has led us to propose that the class B GPCR ligands might have historically evolved as key signals in neuronal pattern formation during embryogenesis. Looking at non-chordate ortholog like DH44 (CRH-like) and DH31 (calcitonin-like) in Drosophila melanogaster, we speculate this might not be an implausible argument.published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Neurobiological role of secretin and its receptor in osmoregulation
No full textOsmoregulation is a survival key for terrestrial animals to defend constant osmotic risks from surroundings. Water imbalance would lead to irreversible damages to major organs, thus a sophisticated physiological and behavioural responses are evolved so as to maintain the constancy of milieu interieur. Recently, Secretin (SCT) has been shown as a neurophysiological factor in osmoregulation. Our previous studies revealed that SCT and its receptor (SCTR) can control water drinking behaviour and vasopressin (Vp) release during dehydration. Moreover, SCT/SCTR axis is required to mediate angiotensin II (ANGII) osmoregulatory actions and, SCTR and angiotensin II receptor type 1 subtype a (AT1aR) are able to form heteromer and regulate hyperosmolality-induced water drinking behaviour. Among the network of central osmoregulatory sites, subfornical organ (SFO) is the most upstream regulator with excitatory and inhibitory efferent to other osmoregulatory brain sites and responsible in detecting and responding to osmolality changes. We have previously shown that SCT and ANGII are capable of stimulating SFO and water intake, however the detailed mechanism of how SCT/SCTR regulates water homeostasis within brain regions and its interaction with AT1aR in Vp release are still unclear.
Due to substantial data showing the close association between SCT and SFO in controlling water drinking, this study firstly investigated if SCT has a specific osmoregulatory action in SFO neurons by using mouse models with SCT or SCTR gene ablation in a SFO cell-specific manner. Under water depletion, SCTSFO-/- and SCTRSFO-/- mice remarkably suppressed water drinking and the differences between water and salt intakes were absent compared with the sham controls. Meanwhile cFos expression and transcript levels in SFO of these specific knockout mice were greatly reduced compared with control, indicating that loss of SCT/SCTR in SFO could suppress neuronal activation in SFO under dehydration, and therefore resulting in reduced water drinking. In line with the electrophysiological data about SCT’s actions on SFO neuron subtypes, it can be concluded that SCT majorly acts on SFO excitatory neurons to promote water intake during dehydration.
Next, the hypothesis that SCTR/AT1aR heteromer mediates Vp release within hypothalamus was extensively examined. Earlier studies have indicated that SCTR/AT1aR heteromer participates in hyperosmolality-induced water intake, yet no information is available concerning the potential interactions of SCTR with AT1aR to control Vp expression and release. In this study, transmembrane (TM) peptides were utilized as biochemical tools to dissect the in vivo actions of SCTR/AT1aR heteromer in paraventricular nucleus (PVN). Central injection of STM2 and ATM4 attenuated SCT/ANGII-induced plasma Vp release and expression in PVN, and central injection of STM2, but not mutant peptides, could also suppress SCT-induced cFos expression in mainly magnocellular PVN cells. Since Vp is produced in magnocellular neurons of PVN, therefore these results indicated that SCTR/AT1aR regulates Vp release and expression in PVN. Furthermore, SCT-induced PKA gene expression in PVN and SCT-induced phosphorylation of pCREB in PVN tissues were reduced when SCTR/AT1aR heteromers were disrupted. Consequently, these results revealed that SCTR/AT1aR heteromer regulates Vp expression and release via cFos/PKA/CREB in magnocellular PVN cells.HKU 3 Minute Thesis Award, 1st Runner-up (2019)published_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Transcriptional regulation of mouse secretin receptor in hypothalamic cells
No full text
As a neuropeptide, both secretin and secretin receptor are expressed in the central nervous system (CNS). It has been revealed that the activities of secretin on hypothalamic cells of rodents are important for osmoregulation and food intake. In the present study, embryonic mouse hypothalamic cell line N42 was used to study the promoter activity of mouse secretin receptor (mSR). By 5′ deletion analysis, a promoter element was identified within ?282 to ?443, relative to the ATG codon, and it contains a GC-box (-297 to -286), a ras responsive element (RRE) (-289 to -276) and an E-box (-416 to -411). Electrophoretic mobility shift assay (EMSA) and supershift analyses showed that Sp1 interacted with the GC-box, another zinc finger
As a neuropeptide, both secretin and secretin receptor are expressed in the central nervous system (CNS). It has been revealed that the activities of secretin on hypothalamic cells of rodents are important for osmoregulation and food intake. In the present study, embryonic mouse hypothalamic cell line N42 was used to study the promoter activity of mouse secretin receptor (mSR). By 5′ deletion analysis, a promoter element was identified within ?282 to ?443, relative to the ATG codon, and it contains a GC-box (-297 to -286), a ras responsive element (RRE) (-289 to -276) and an E-box (-416 to -411). Electrophoretic mobility shift assay (EMSA) and supershift analyses showed that Sp1 interacted with the GC-box, another zinc fingerpublished_or_final_versionBiological SciencesDoctoralDoctor of Philosoph
Transcriptional regulation of the human secretin receptor gene
No full textpublished_or_final_versionZoologyDoctoralDoctor of Philosoph
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