| Summary: | Over the last years there has been an improved understanding of the underlying mechanisms involved in nutrient sensing, and how the gastrointestinal tract (GIT) conveys information on ingested food to the brain and other organs. In mammals, several receptors from the G protein‐coupled receptors (GPCRs) superfamily have been identified as nutrient sensors that respond to organic nutrients or their breakdown products, i.e. fatty acids, sugars, amino acids (AAs) and proteolytic products. The AAs and peptides sensory mechanisms in the GIT are involved in modulating pancreatic exocrine and endocrine secretions as well as protein digestion in order to optimize nutrient utilization and control feed intake. While it is well acknowledged that the nutrient sensing system is a key player in the control of these functions in mammals, almost no information exist in teleosts, the largest vertebrate group with more than 25000 species. In Atlantic salmon ( Salmo salar ), a key commercial species in global aquaculture, it is of high interest to understand how specific AA enhance feed intake, growth and fish quality. In addition, Atlantic salmon has undergone an additional and relatively recent whole‐genome duplication event, the salmonid‐specific 4th WGD. Atlantic salmon therefore represent an excellent model system to study the role of gene duplication and adaptation. Key mammalian GPCRs involved in AA and peptide sensing in GIT belong to GPCR family C and A, respectively. The lysophosphatidic acid receptor 5 (LPAR5) belongs to family A and is responsive to peptides. The family C consists of members such as the metabotropic glutamate receptors (mGluRs), calcium‐sensing receptor (CasR), GPCR family C subtype 6A (GPRC6A) and taste receptors (T1Rs). Whereas the mGluRs are monogamous for L‐Glu, the CasR, GPR6A and T1Rs are promiscuous by nature and respond to, e.g., subsets of L‐α‐AAs and divalent cations. Such promiscuity for nutrients by the receptors in relevant tissues allows for a specific nutrient‐sensing capacity of emerging ...
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