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Tissue distribution showed that ctrp was abundantly expresse
Tissue distribution showed that ctrp9 was abundantly expressed in the kidney of male and female tilapia. In mice, the Ctrp9 was identified in adipose tissue, and the expression levels were higher in females than that of males (Wong et al., 2009). Recent studies indicated that Ctrp9 was also expressed in heart and the expression levels of Ctrp9 were higher in heart than that of adipose tissue (Appari et al., 2017, Breitbart et al., 2013). Moreover, the expression level of ctrp9 was also most abundant in the kidney of grouper (Yang et al., 2017), and ctrp9 was mostly expressed in the intestine and kidney of lamprey (Chen et al., 2016). In this study, the expression of adipor1 and adipor2 were widely distributed in all tissues of tilapia. Previous studies indicated that AdipoR1 and AdipoR2 reported in other species had a wide range of distribution, including fish (Qin et al., 2014, Sanchez-Gurmaches et al., 2012), chicken (Ramachandran et al., 2007) and mammals (Kadowaki and Yamauchi, 2005, Yamauchi et al., 2003). The wide range of expression suggest that adiponectin receptors possess multiple biological functions in vertebrates. The expression levels of adipor1/2 were higher in the hypothalamus and Ezatiostat receptor regions of tilapia. Initial studies showed that AdipoRs were expressed in the brain, pituitary, hypothalamus and POMC (proopiomelanocortin) and NPY (Neuropeptide Y) neurons (Guillod-Maximin et al., 2009, Rodriguez-Pacheco et al., 2007, Yamauchi et al., 2003) in mammals. Moreover, adipors were expressed in CNS (central nervous system) in grouper (Qin et al., 2014). Our results revealed that the expression of adipor1/2 were abundant in the gonad of tilapia, in line with previous studies in rat, pig, chicken and fish (Chabrolle et al., 2007, Lord et al., 2005, Qin et al., 2014, Ramachandran et al., 2007). In addition, the studies indicated that AdipoRs mRNA levels in ovary is equal to that of in liver (Ramachandran et al., 2007). Qin and colleagues reported that the adipor2 mRNA expression was highest in the gonad of grouper (Qin et al., 2014). Furthermore, the AdipoRs were also expressed in rat and human testis (Caminos et al., 2008, Civitarese et al., 2004). Overall, the AdipoRs expression in the gonad is an universal phenomenon. The high expression levels of adipors is also in the gut and stomach in tilapia. It is speculated that the Adipors may be involved in digestion and resorption in tilapia.
The CTRP9 gene / protein level was regulated by many factors during different physiological processes. Female mice expresses higher levels of the Ctrp9 transcript than males and the Ctpr9 expression levels in ob/ob mice changed in an age-dependent manner (Wong et al., 2009). In human, serum CTRP9 was significantly higher in the obese group compared to the lean group (Wolf et al., 2016). In subjects with type 2 diabetes, the elevated serum CTRP9 concentration were significantly associated with gender, higher body mass index, and homeostatic model assessment of insulin resistance (Jung et al., 2014). And in type 2 diabetes, serum CTRP9 concentrations were significantly correlated with leptin. When subjected to multiple regression analysis, leptin was predictive of serum CTRP9 concentrations (Bai et al., 2017). After fasted 7 days, the ctrp9 gene expression was decreased in grouper liver and was restored back to the normal levels after refeeding (Yang et al., 2017). The CTRP9 level was also associated with the immune factors. In the coronary atherosclerosis disease patients, serum level of CTRP9 was negatively related to TNF-α and IL-6 (Wang et al., 2015).
Conclusion
In conclusion, we have identified the sequences of Ctrp9, Adipor1 and Adipor2 in tilapia, and examined their tissue distribution of both sexes. The recombinant gCtrp9 markedly decrease the genes expression related to reproduction in HPG axis and reduce the levels of sex hormone in serum of tilapia after i.p injection. To the best of our knowledge, our data, for the first time, provides evidence for a regulative effect of Ctrp9 on reproduction in a teleost. To clarify the mechanism underlying the impact of Ctrp9 on the regulation of reproduction in tilapia, studies on the interaction of Ctrp9 and Adipor1 and Adipor2 is currently underway.