No abstract

Type II suppressor of cytokine signaling (SOCS) serve as feedback repressors for cytokines and are known to inhibit growth hormone (GH) actions. However, direct evidence for SOCS modulation of GH-induced insulin-like growth factor 1 (Igf1) expression is lacking, and the post-receptor signaling for SOCS expression at the hepatic level is still unclear. To shed light on the comparative aspects of SOCS in GH functions, grass carp was used as a model to study the role of type II SOCS in GH-induced Igf1 expression. Structural identity of type II SOCS, Socs1-3 and cytokine-inducible SH2-containing protein (Cish), was established in grass carp by 5'/3'-RACE, and their expression at both transcript and protein levels were confirmed in the liver by RT-PCR and LC/MS/MS respectively. In carp hepatocytes, GH treatment induced rapid phosphorylation of JAK 2 , STATs, MAPK, PI3K, and protein kinase B (Akt) with parallel rises in socs1-3 and cish mRNA levels, and these stimulatory effects on type II SOCS were shown to occur before the gradual loss of igf1 gene expression caused by prolonged exposure of GH. Furthermore, GH-induced type II SOCS gene expression could be negated by inhibiting JAK 2 , STATs, MEK 1/2 , P 38 MAPK , PI3K, and/or Akt respectively. In CHO cells transfected with carp GH receptor, over-expression of these newly cloned type II SOCS not only suppressed JAK 2 /STAT 5 signaling with GH treatment but also inhibited GH-induced grass carp Igf1 promoter activity. These results, taken together, suggest that type II SOCS could be induced by GH in the carp liver via JAK 2 /STATs, MAPK, and PI3K/Akt cascades and serve as feedback repressors for GH signaling and induction of igf1 gene expression.

We identified extracellular signal-regulated kinase 2 (erk2) from green mud crab, Scylla paramamosain, in this article. It was originally identified from an expressed sequence tag fragment from a normalized gonadal cDNA library. 5¢ Rapid amplification of cDNA end (RACE) technique was used to obtain the 5¢ untranslated region (UTR). The full-length cDNA of Sp-erk2 is 1516 bp, including a 5¢-terminal UTR of 19 bp, an open-reading frame of 1098 bp, and a 3¢-terminal UTR of 399 bp. The translated protein is 365 amino acids in length with a predicted molecular weight of 42 kDa, which is the same as other species. It is the first time that the expression of Sp-erk2 in different stages of ovary development of crustacean was analyzed, and the result showed that the expression of Sp-erk2 increased gradually with ovarian development, with a peak in the mature phase. In situ hybridization histochemistry was used to clarify the detail of expression. Positive signals illustrated that Sp-erk2 mRNA is present in follicular cells when the ovary is in early stages, and in both follicular cells and oocytes when it is in mature phases. All above suggest that Sp-erk2 is important for ovarian development.

No abstract

Insulin is a key hormone for metabolism and glucose homeostasis. In mammals, it also acts as a satiety factor with inhibitory effect on food intake, but its biological actions in appetite control in lower vertebrates is still unknown. Spexin (SPX), a neuropeptide with pleotropic functions, has been recently confirmed to be a novel satiety factor in fish model via functional coupling with insulin, although the details of their interactions have yet to be elucidated. In this study, using goldfish as a model, the mechanism for feeding regulation by insulin and its functional interactions with SPX at hepatic level were examined. As a first step, goldfish insulin was cloned and found to be widely expressed at tissue level, especially with high levels of expression in the liver and visceral fat. In silico modeling also showed that the 3D structure of the mature peptide of goldfish insulin was highly comparable if not identical to its human counterpart. In goldfish liver cell culture, insulin mRNA level could be up-regulated by SPX treatment via PLC/IP 3 /PKC and Ca 2+ /CaM/CaMK-II pathways, while the opposite was true by removing endogenous SPX using immunoneutralization with SPX antiserum. In whole animal experiment, IP injection with insulin was found to inhibit feeding behavior and food consumption in goldfish. Similar treatment in vivo was also effective in elevating POMC, CART, CCK and leptin mRNA levels with concurrent drop in NPY, AGRP and apelin transcript expression in the telencephalon, optic tectum and hypothalamus, the brain areas known to be involved in feeding control in fish models. Using brain cell culture prepared from these three areas, similar changes in transcript expression for the respective orexigenic and anorexigenic factors were also noted with insulin treatment in a time- and dose-dependent manner. These findings, as a whole, suggest that SPX can act in an autocrine/paracrine manner to induce insulin expression in goldfish liver and the subsequence rise of insulin in circulation presumably can inhibit food intake through differential regulation of orexigenic/anorexigenic signals expressed in brain areas involved in appetite control in fish model.