Isolation and characterization of a mRNA encoding a novel insulin receptor (IR) subtype, IR2, from rainbow trout (Oncorhynchus mykiss) and patterns of expression of the four IR subtypes, IR1–IR4, in tissues and during embryonic development

In vitro insulin treatment reverses changes elicited by nutrients in cellular metabolic processes that regulate food intake in fish

“…The different actions observed for insulin in the hypothalamus versus the hindbrain may rely on a differential distribution of insulin receptors in these two tissues or on the fact that a different receptor subtype is mediating insulin actions in each location. Four distinct insulin receptors have been identified in rainbow trout, which are differentially expressed in the brain (Caruso et al, 2010). While no study is available on the distribution of the four receptor subtypes within the specific areas of the rainbow trout brain, the fact that they show a differential expression level in the brain opens the possibility of different expression levels in the hypothalamus and hindbrain, which could explain the tissue-specific actions observed here.…”

“…Insulin penetrates the blood-brain barrier (Gray et al, 2014) and binds to receptors located in brain regions including the hypothalamus and hindbrain (Arble and Sandoval, 2013). The presence of insulin receptors in the brain of fish, including rainbow trout (Caruso et al, 2010) and other species (Cruz et al, 2010;Ma et al, 2017), has been previously reported. Additionally, central actions of insulin could relate to its synthesis in brain, as demonstrated in several fish species (Caruso and Sheridan, 2011;Hrytsenko et al, 2008;Ma et al, 2017;Papasani et al, 2006).…”

“…Most of the observed variability is, however, in the C-peptide region of the preproinsulin (Caruso et al, 2008), which is removed during processing, resulting in a mature insulin peptide with a similar tertiary structure between rainbow trout and mammals (61.9% for insulin chain A and 79.3% for insulin chain B) (Caruso and Sheridan, 2011). Moreover, rainbow trout insulin receptors share the basic structural features of mammalian receptors (Caruso et al, 2010). Wortmannin has also been successfully used in fish models to block insulin actions (Paul et al, 2009).…”

Effects of insulin treatment on the response to oleate and octanoate of food intake and fatty acid–sensing systems in rainbow trout

“…Despite increased levels of circulating FA are known to elicit insulin release in fish [18], information about insulin action on lipid metabolism in fish is scarce and contradictory [19,20], and no evidence is available regarding the possible modulatory role of insulin on FAsensing systems. In rainbow trout, the expression of insulin receptors has been demonstrated in different tissues including hypothalamus and liver [21,22]. Also, in this species, insulin administration modulates brain glucosensing system [23][24][25] and inhibits FI [26].…”

Insulin receptors in largemouth bass ( Micropterus salmoides ): Cloning, characterization, tissue expression profile and transcriptional response to glucose tolerance test

“…The IRs have been isolated and characterized for some teleosts, and multiple but distinct IR‐encoding mRNAs have been identified. For example, four IRs (IR1, IR2, IR3 and IR4) are observed in the rainbow trout, Oncorhynchus mykiss (Caruso et al., 2010), while two IRs (IRa and IRb) have been detected in the turbot ( Psetta maxima ), grass carp ( Ctenopharyngodon idellus ), Japanese flounder ( Paralichthys olivaceus ) and zebrafish ( Danio rerio ) (Cai et al., 2016; Elies et al., 1999; Nakao et al., 2002; Toyoshima et al., 2008). In mammals, the binding of insulin to the α‐subunit of IRs may promote the phosphorylation of tyrosine in its own β‐subunit, to activate the downstream signal (Taniguchi et al., 2006).…”