鱼类生长抑素及其受体的研究进展

Progress of research on fish somatostatin and receptor

A central component of fish growth coordination is the Growth hormone-Insulin-like Growth Factor-Ⅰ(GH-IGF-Ⅰ) axis.The GH-IGFⅠ axis begins with GH production in the pituitary gland under the control of multiple hypothalamic hormones,including somatostatin(SS).SS have been proved to possess a variety of biological functions with widely distribution in the central nervous system and peripheral tissues.It plays roles in the physiological process of the central nervous system,modulating growth,development and metabolism processes.Research results on mammalian SS have been applied to produce new medicines.Research on fish somatostatin have lasted for over 25 years,and it has received more and more attentions.Fish is an important animal model and one of the important protein source of human,research on fish SS can help to understand the physiology roles of SS and to regulate fish growth and other physiologic processes.Mammalian SS exists as two predominant biologically active forms, SS14 peptide and its N-terminal extensions of 14 amino acids,SS28.Both SS14 and SS28 are encoded by a common gene and processed from a single precursor,PSSI.SS14 is highly conserved in all known vertebrate species,including several mammalian species,chicken,frog and fishes,with the same amino acid sequence.In addition to having PSSI,Fish possess one or two other different forms of somatostatin(SS),PSSⅡ and PSSⅢ.The PSSⅡ molecule is thought to be processed to a large form of SS(SS28 or SS25) with [Tyr7,Gly10]-SS14 at its C-terminus,while the PSSⅢ would produce a SS14 variant-SS14.All the three types of PSS genes had been cloned both in goldfish and Orange-spotted grouper.PSSs are widely distributed throughout the central nervous system(CNS) and peripheral tissues. PSS are differentially expressed,both in terms of the distribution among tissues and in terms of the relative abundance within a tissue.SS exerts diverse inhibitory actions through binding to specific membrane-bound G-protein-coupled receptors.There are different types of somatostatin receptor(Sst) with widely and completely distribution patterns.4 types of Sst had been cloned in fish.Researches results showed that SSs regulate growth and interact with reproduction, development and metabolism processes.SSs elicit their effects through a multifaceted signaling system consisting of several Sst.They influences organism growth on the GH-IGF-I axis through pituitary as well as through liver.SSs influence other growth related hormone systems and coordinate these systems with the GH-IGF-I axis to regulate the fish growth.Despite recent research progress,our understanding of the complex mechanisms through which SS modulates growth is only in the beginning stages.Many more studies will be necessary to fully describe the complex system and to understand the biological significance of the complexity.Future studies will need to answer the questions such as whether SS the main factor regulates the releasing of GH,whether a type of SS peptide connects with a special receptor,how many subtypes of receptor needed for SS to exert a kind of physiological function,etc.Ultimately,such work will lead to a better understanding of how SS regulate growth in fish and how growth is coordinated with reproduction and metabolism.

A central component of fish growth coordination is the Growth hormone - Insulin - like Growth Factor- Ⅰ （GH-IGF-Ⅰ ） axis. The GH-IGF-Ⅰ axis begins with GH production in the pituitary gland under the control of multiple hypothalamic hormones, including somatostatin （SS）. SS have been proved to possess a variety of biological functions with widely distribution in the central nervous system and peripheral tissues. It plays roles in the physiological process of the central nervous system, modulating growth, development and metabolism processes. Research results on mammalian SS have been applied to produce new medicines. Research on fish somatostatin have lasted for over 25 years, and it has received more and more attentions. Fish is an important animal model and one of the important protein source of human, research on fish SS can help to understand the physiology roles of SS and to regulate fish growth and other physiologic processes. Mammalian SS exists as two predominant biologically active forms, SS14 peptide and its N-terminal extensions of 14 amino acids, SSzs. Both SS14 and SSzs are encoded by a common gene and processed from a single precursor, PSSI. SS14 is highly conserved in all known vertebrate species, including several mammalian species, chicken, frog and fishes, with the same amino acid sequence. In addition to having PSSI, Fish possess one or two other different forms of somatostatin （ SS）, PSS Ⅱ and PSS Ⅲ. The PSS Ⅱ molecule is thought to be processed to a large form of SS （SSzs or SS25） with [Tyr^7 ,GIy^10 ]-SS14 at its C-terminus, while the PSS Ⅲ would produce a SS14 variant[ Pro^2]-SS14. All the three types of PSS genes had been cloned both in goldfish and Orange-spotted grouper. PSSs are widely distributed throughout the central nervous system （CNS） and peripheral tissues. PSS are differentially expressed, both in terms of the distribution among tissues and in terms of the relative abundance within a tissue. SS exerts diverse inhibitory actions through binding to specific membrane-bound G-protein-coupled receptors. There are different types of somatostatin receptor （Sst） with widely and completely distribution patterns. 4 types of Sst had been cloned in fish. Researches results showed that SSs regulate growth and interact with reproduction, development and metabolism processes. SSs elicit their effects through a multifaceted signaling system consisting of several Sst. They influences organism growth on the GH-IGF-I axis through pituitary as well as through liver. SSs influence other growth related hormone systems and coordinate these systems with the GH-IGF-I axis to regulate the fish growth. Despite recent research progress, our understanding of the complex mechanisms through which SS modulates growth is only in the beginning stages. Many more studies will be necessary to fully describe the complex system and to understand the biological significance of the complexity. Future studies will need to answer the questions such as whether SS the main factor regulates the releasing of GH, whether a type of SS peptide connects with a special receptor, how many subtypes of receptor needed for SS to exert a kind of physiological function, etc. Ultimately, such work will lead to a better understanding of how SS regulate growth in fish and how growth is coordinated with reproduction and metabolism.