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Martinez-Silva MA, Dupont-Prinet A, Houle C, Vagner M, Garant D, Bernatchez L, Audet C. Growth regulation in brook charr Salvelinus fontinalis. Gen Comp Endocrinol 2023; 331:114160. [PMID: 36356646 DOI: 10.1016/j.ygcen.2022.114160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 09/12/2022] [Accepted: 11/02/2022] [Indexed: 11/09/2022]
Abstract
Fish growth can be modulated through genetic selection. However, it is not known whether growth regulatory mechanisms modulated by genetic selection can provide information about phenotypic growth variations among families or populations. Following a five-generation breeding program that selected for the absence of early sexual maturity and increased growth in brook charr we aimed to understand how the genetic selection process modifies the growth regulatory pathway of brook charr at the molecular level. To achieve this, we studied the regulation of growth traits at three different levels: 1) between lines-one under selection, the other not, 2) among-families expressing differences in average growth phenotypes, which we termed family performance, and 3) among individuals within families that expressed extreme growth phenotypes, which we termed slow- and fast-growing. At age 1+, individuals from four of the highest performing and four of the lowest performing families in terms of growth were sampled in both the control and selected lines. The gene expression levels of three reference and ten target genes were analyzed by real-time PCR. Results showed that better growth performance (in terms of weight and length at age) in the selected line was associated with an upregulation in the expression of genes involved in the growth hormone (GH)/insulin growth factor-1 (IGF-1) axis, including the igf-1 receptor in pituitary; the gh-1 receptor and igf-1 in liver; and ghr and igf-1r in white muscle. When looking at gene expression within families, family performance and individual phenotypes were associated with upregulations of the leptin receptor and neuropeptid Y-genes related to appetite regulation-in the slower-growing phenotypes. However, other genes related to appetite (ghrelin, somatostatin) or involved in muscle growth (myosin heavy chain, myogenin) were not differentially expressed. This study highlights how transcriptomics may improve our understanding of the roles of different key endocrine steps that regulate physiological performance. Large variations in growth still exist in the selected line, indicating that the full genetic selection potential has not been reached.
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Affiliation(s)
| | - Aurélie Dupont-Prinet
- Institut des Sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, QC G5L 3A1, Canada
| | - Carolyne Houle
- Département de Biologie, Université du Sherbrooke, Sherbrooke, QC J1K 2R1, Canada
| | - Marie Vagner
- Laboratoire des Sciences de l'Environnement Marin, UMR 6539 (CNRS/Univ Brest/IRD/Ifremer), Plouzané 29280, France
| | - Dany Garant
- Département de Biologie, Université du Sherbrooke, Sherbrooke, QC J1K 2R1, Canada
| | - Louis Bernatchez
- Institut de Biologie Intégrative et des Systèmes (IBIS), Département de Biologie, Université du Laval, Québec, QC G1V 0A6, Canada
| | - Céline Audet
- Institut des Sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, QC G5L 3A1, Canada
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Hu F, Zhao Y, Dong F, Wang H, Zheng M, Zhang W, Chen X. Insights into the mechanisms of tris(2-chloroethyl) phosphate-induced growth inhibition in juvenile yellow catfish Pelteobagrus fulvidraco. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2022; 247:106170. [PMID: 35468409 DOI: 10.1016/j.aquatox.2022.106170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 03/28/2022] [Accepted: 04/06/2022] [Indexed: 06/14/2023]
Abstract
With the gradual elimination of brominated flame retardants (BFRs), the production and application of tris (2-chloroethyl) phosphate (TCEP), as a substitute of BFRs, has increased greatly. The objective of the present study was to comprehensively explore the potential adverse effects of TCEP on fish growth and the possible underlying mechanisms. To this end, juvenile yellow catfish (Pelteobagrus fulvidraco) were exposed to environmentally relevant concentrations of TCEP (0, 1, 10 and 100 µg/L) for 30 days. The results showed that exposure to high concentrations of TCEP (10 and 100 µg/L) significantly decreased body weight, body length and specific growth rate (SGR). Plasma IGF-I levels and hepatic mRNA levels of igf1 and igf1r were all reduced, while the transcriptional levels of IGFBPs (igfbp2, igfbp3, igfbp5) were significantly up-regulated in the liver of yellow catfish under exposure to 10 and 100 µg/L TCEP. TCEP-induced growth inhibition might be related to somatostatin (SS) signaling system, as evidenced by elevated mRNA transcriptions of ss in brain and its receptors (sstr2, sstr3, sstr5) in liver. In addition, fish exposed to high concentrations of TCEP displayed multiple histological alterations in liver. Taken together, these findings suggested that TCEP (>10 µg/L) might exert its inhibitory effect on fish growth through interfering with the GH/IGF axis and SS signaling system, and by impairing hepatic structures.
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Affiliation(s)
- Fengxiao Hu
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Yixin Zhao
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Feilong Dong
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Hongkai Wang
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Mengyan Zheng
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Weini Zhang
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Xinhua Chen
- Key Laboratory of Marine Biotechnology of Fujian Province, Institute of Oceanology, Fujian Agriculture and Forestry University, Fuzhou 350002, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China.
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Chandhini S, Trumboo B, Jose S, Varghese T, Rajesh M, Kumar VJR. Insulin-like growth factor signalling and its significance as a biomarker in fish and shellfish research. FISH PHYSIOLOGY AND BIOCHEMISTRY 2021; 47:1011-1031. [PMID: 33987811 DOI: 10.1007/s10695-021-00961-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 05/04/2021] [Indexed: 06/12/2023]
Abstract
The insulin-like growth factor signalling system comprises insulin-like growth factors, insulin-like growth factor receptors and insulin-like growth factor-binding proteins. Along with the growth hormones, insulin-like growth factor signalling is very pivotal in the growth and development of all vertebrates. In fishes, insulin-like growth factors play an important role in osmoregulation, besides the neuroendocrine regulation of growth. Insulin-like growth factor concentration in plasma can assess the growth in fishes and shellfishes and therefore widely applied in nutritional research as an indicator to evaluate the performance of selected nutrients. The present review summarizes the role of insulin-like growth factor signalling in fishes and shellfishes, its significance in aquaculture and in evaluating growth, reproduction and development, and discusses the utility of this system as biomarkers for early indication of growth in aquaculture.
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Affiliation(s)
- S Chandhini
- Centre of Excellence in Sustainable Aquaculture and Aquatic Animal Health Management (CAAHM), Department of Aquaculture, Kerala University of Fisheries and Ocean Studies, Panangad, Kochi, 682506, Kerala, India
| | - Bushra Trumboo
- Centre of Excellence in Sustainable Aquaculture and Aquatic Animal Health Management (CAAHM), Department of Aquaculture, Kerala University of Fisheries and Ocean Studies, Panangad, Kochi, 682506, Kerala, India
| | - Seena Jose
- National Centre for Aquatic Animal Health, Cochin University of Science and Technology, Kochi, 682016, Kerala, India
| | - Tincy Varghese
- Fish Physiology and Biochemistry Division, ICAR-Central Institute of Fisheries Education, Off-Yari Road, Versova, Andheri (W), Mumbai, 400061, India
| | - M Rajesh
- ICAR-Directorate of Coldwater Fisheries Research, Anusandhan Bhawan, Bhimtal, 263136, Uttarakhand, India
| | - V J Rejish Kumar
- Centre of Excellence in Sustainable Aquaculture and Aquatic Animal Health Management (CAAHM), Department of Aquaculture, Kerala University of Fisheries and Ocean Studies, Panangad, Kochi, 682506, Kerala, India.
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Feng P, Tian C, Lin X, Jiang D, Shi H, Chen H, Deng S, Zhu C, Li G. Identification, Expression, and Functions of the Somatostatin Gene Family in Spotted Scat ( Scatophagus argus). Genes (Basel) 2020; 11:genes11020194. [PMID: 32059553 PMCID: PMC7073721 DOI: 10.3390/genes11020194] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 01/31/2020] [Accepted: 02/07/2020] [Indexed: 12/24/2022] Open
Abstract
Somatostatins (SSTs) are a family of proteins consisting of structurally diverse polypeptides that play important roles in the growth regulation in vertebrates. In the present study, four somatostatin genes (SST1, SST3, SST5, and SST6) were identified and characterized in the spotted scat (Scatophagus argus). The open reading frames (ORFs) of SST1, SST3, SST5, and SST6 cDNA consist of 372, 384, 321, and 333 bp, respectively, and encode proteins of 123, 127, 106, and 110 amino acids, respectively. Amino acid sequence alignments indicated that all SST genes contained conserved somatostatin signature motifs. Real-time PCR analysis showed that the SST genes were expressed in a tissue specific manner. When liver fragments were cultured in vitro with synthetic peptides (SST1, SST2, or SST6 at 1 μM or 10 μM) for 3 h or 6 h, the expression of insulin-like growth factor 1 and 2 (Igf-1 and Igf-2) in the liver decreased significantly. Treatment with SST5 had no significant effect on Igf-1 and Igf-2 gene expression. This study provides an enhanced understanding of the gene structure and expression patterns of the SST gene family in S. argus. Furthermore, this study provides a foundation for future exploration into the role of SST genes in growth and development.
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Affiliation(s)
- Peizhe Feng
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
| | - Changxu Tian
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Xinghua Lin
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
| | - Dongneng Jiang
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Hongjuan Shi
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Huapu Chen
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Siping Deng
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Chunhua Zhu
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
| | - Guangli Li
- Fisheries College, Guangdong Ocean University, Zhanjiang 524088, China; (P.F.); (C.T.); (X.L.); (D.J.); (H.S.); (H.C.); (S.D.); (C.Z.)
- Guangdong Research Center on Reproductive Control and Breeding Technology of Indigenous Valuable Fish Species, Zhanjiang 524088, China
- Marine Ecology and Aquaculture Environment of Zhanjiang, Zhanjiang 524088, China
- Correspondence: ; Tel.: +86-75-92-383-124; Fax: +86-75-92-382-459
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Reindl KM, Sheridan MA. Peripheral regulation of the growth hormone-insulin-like growth factor system in fish and other vertebrates. Comp Biochem Physiol A Mol Integr Physiol 2012; 163:231-45. [DOI: 10.1016/j.cbpa.2012.08.003] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Revised: 08/03/2012] [Accepted: 08/07/2012] [Indexed: 10/28/2022]
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Shimomura T, Nakajima T, Horikoshi M, Iijima A, Urabe H, Mizuno S, Hiramatsu N, Hara A, Shimizu M. Relationships between gill Na⁺,K⁺-ATPase activity and endocrine and local insulin-like growth factor-I levels during smoltification of masu salmon (Oncorhynchus masou). Gen Comp Endocrinol 2012; 178:427-35. [PMID: 22749841 DOI: 10.1016/j.ygcen.2012.06.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 04/17/2012] [Accepted: 06/12/2012] [Indexed: 01/28/2023]
Abstract
We established profiles of insulin-like growth factor (IGF)-I mRNA in the liver, gill and white muscle and circulating IGF-I during smoltification of hatchery-reared masu salmon, and compared with that of gill Na(+),K(+)-ATPase (NKA) activity. Gill NKA activity peaked in May and dropped in June. Liver igf1 mRNA was high in March and decreased to low levels thereafter. Gill igf1 increased from March, maintained its high levels during April and May and decreased in June. Muscle igf1 mRNA levels were relatively high during January and April when water temperature was low. Serum IGF-I continuously increased from March through June. Serum IGF-I during March and May showed a positive correlation with NKA activity, although both were also related to fish size. These parameters were standardized with fork length and re-analyzed. As a result, serum IGF-I and gill igf1 were correlated with NKA activity. On the other hand, samples from desmoltification period (June) that had high serum IGF-I levels and low NKA activity disrupted the relationship. Expression of two IGF-I receptor (igf1r) subtypes in the gill decreased in June, which could account for the disruption by preventing circulating IGF-I from acting on the gill and retaining it in the blood. The present study suggests that the increase in gill NKA activity in the course of smoltification of masu salmon was supported by both endocrine and local IGF-I, and the decrease during desmoltification in freshwater was due at least in part to the down-regulation of gill IGF-I receptors.
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Affiliation(s)
- Takahiro Shimomura
- Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan
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Sheridan MA, Hagemeister AL. Somatostatin and somatostatin receptors in fish growth. Gen Comp Endocrinol 2010; 167:360-5. [PMID: 19735661 DOI: 10.1016/j.ygcen.2009.09.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Revised: 08/20/2009] [Accepted: 09/02/2009] [Indexed: 01/25/2023]
Abstract
Multiple forms of somatostatin (SS) and SS receptors (SSTR) are produced widely in the tissues of fish and interact to coordinate numerous physiological processes. Insight into their role in growth regulation emerged from studies of abnormal growth and of whole animals. The influence of SS on organismal growth operates at several levels of the growth hormone (GH)-insulin-like growth factor-1 (IGF-1) system. SS inhibits production and release of pituitary GH, but not all forms of SS are equipotent in this action. SS also influences the GH-IGF-1 system in an extrapituitary manner by reducing sensitivity to GH as well as by inhibiting IGF-1 production and secretion, and diminishing IGF-1 sensitivity. Peripheral actions of SS are important for the local control of growth and may help to coordinate growth with other processes such as metabolism, development, and reproduction by reprogramming cell responsiveness.
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Affiliation(s)
- Mark A Sheridan
- Department of Biological Sciences, North Dakota State University, Fargo, ND 58108-6050, USA.
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Hanson A, Poudyal D, Hagemeister A, Reindl KM, Sheridan MA. The ERK and PI3K signaling pathways mediate inhibition of insulin-like growth factor-1 receptor mRNA expression by somatostatin. Mol Cell Endocrinol 2010; 315:57-62. [PMID: 19815052 DOI: 10.1016/j.mce.2009.09.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Revised: 09/28/2009] [Accepted: 09/30/2009] [Indexed: 01/11/2023]
Abstract
Somatostatins (SSs) are a structurally diverse family of peptide hormones that regulate various aspects of growth, development, and metabolism in vertebrates. Previously, we showed that SSs inhibit mRNA and functional expression of insulin-like growth factor-1 receptors (IGFR1) in gill filaments of rainbow trout. In this study, we used trout gill filaments, which express in high abundance two distinct IGFR1s, IGFR1A and IGFR1B, to examine the mechanism(s) through which SSs exert their inhibitory effects on IGFR1 expression. SS-14, a predominat SS isoform, directly stimulated the phosphorylation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt), a downstream target of phosphatidylinositol 3-kinase (PI3K), in filaments incubated in vitro. Activation of ERK and Akt by SS-14 was rapid, occuring within 5-10 min, and was concentration-dependent. The ERK pathway inhibitor, U0126, retarded SS-14-stimulated phosphorylation of ERK 1/2, whereas the PI3K inhibitor, LY294002, blocked SS-14-stimulated phosphorylation of Akt. SS-14-inhibited expression of IGFR1 mRNAs was blocked by both U0126 and LY294002. These data indicate that SS-14 inhibition of IGFR1 mRNA expression is mediated through the ERK and PI3K/Akt signaling pathways.
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Affiliation(s)
- Andrea Hanson
- Department of Biological Sciences, North Dakota State University, Fargo, ND 58108-6050, USA
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Malkuch H, Walock C, Kittilson JD, Raine JC, Sheridan MA. Differential expression of preprosomatostatin- and somatostatin receptor-encoding mRNAs in association with the growth hormone-insulin-like growth factor system during embryonic development of rainbow trout (Oncorhynchus mykiss). Gen Comp Endocrinol 2008; 159:136-42. [PMID: 18783723 DOI: 10.1016/j.ygcen.2008.08.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Revised: 08/15/2008] [Accepted: 08/18/2008] [Indexed: 01/13/2023]
Abstract
Rainbow trout were used to evaluate the relationship between the somatostatin (SS) signaling and the growth hormone (GH)-insulin-like growth factor (IGF) systems during pre-hatch and post-hatch embryonic development. The expression of preprosomatostatins (PPSS), SS receptors (SSTR), GH receptors (GHR), IGF-1, IGF-2, and IGF type 1 receptors (IGFR1) was examined in various regions at the eyed-egg (29 days post-fertilization, dpf;), post-hatch (53dpf), swim-up (68dpf), and complete yolk-absorbed (90dpf) stages. In head, PPSSI mRNA abundance increased during development while that of PPSSII' decreased and that of PPSSII'' remained unchanged. In body and tail, mRNA abundance of all PPSSs remained unchanged except that of PPSSII'' which declined in the tail. SSTR expression increased as development progressed in all regions with the exception of SSTR1A mRNA which remained unchanged. mRNA levels of GHR1 declined in all regions of post-hatch embryos, whereas those of GHR2 remained unchanged. Expression of IGF-1 and IGF-2 in head and tail regions increased immediately after hatching, and then declined, whereas the expression of neither IGF changed during development in the body. The expression of IGFR1 mRNAs declined in all regions, reaching their lowest levels at 90dpf, with the exception of IGFR1A mRNA in the body which remained unchanged. The general decline in the expression of GH-IGF system components during development appears inversely related to a general increase in the expression of SS system elements, and suggests that these two systems interact to regulate the tissue expansion and tissue regression of embryogenesis.
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Affiliation(s)
- Heidi Malkuch
- Department of Biological Sciences, North Dakota State University, Stevens Hall, Fargo, ND 58105, USA
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Hagemeister AL, Sheridan MA. Somatostatin inhibits hepatic growth hormone receptor and insulin-like growth factor I mRNA expression by activating the ERK and PI3K signaling pathways. Am J Physiol Regul Integr Comp Physiol 2008; 295:R490-7. [DOI: 10.1152/ajpregu.00099.2008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previously, we reported that somatostatins (SS) inhibit organismal growth by reducing hepatic growth hormone (GH) sensitivity and by inhibiting insulin-like growth factor I (IGF-I) production. In this study, we used hepatocytes isolated from rainbow trout to elucidate the mechanism(s) associated with the extrapituitary growth-inhibiting actions of SS. SS-14, a predominant SS isoform, stimulated tyrosine phosphorylation of several endogenous proteins, including extracellular signal-regulated kinase (ERK), a member the mitogen-activated protein kinase (MAPK) family, and protein kinase B (Akt), a downstream target of phosphatidylinositol 3-kinase (PI3K). SS-14 specifically stimulated the phosphorylation of both ERK 1/2 and Akt in a concentration-dependent fashion. This activation occurred within 5–15 min, then subsided after 1 h. The ERK inhibitor U0126 retarded SS-14-stimulated phosphorylation of ERK 1/2, whereas the PI3K inhibitor LY294002 blocked SS-14-stimulated phosphorylation of Akt. SS-14-inhibited expression of GH receptor (GHR) mRNA was blocked by U0126 but not by LY294002. By contrast, U1026 had no effect on SS-14 inhibition of GH-stimulated IGF-I mRNA expression, whereas LY294002 partially blocked the inhibition of GH-stimulated IGF-I mRNA expression by SS-14. These results indicate that SS-14-inhibited GHR expression is mediated by the ERK signaling pathway and that the PI3K/Akt pathway mediates, at least in part, SS-14 inhibition of GH-stimulated IGF-I expression.
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