The pro-opiomelanocortin genes in rainbow trout (Oncorhynchus mykiss): duplications, splice variants, and differential expression

Abstract

Pro-opiomelanocortin (POMC) is a precursor for several important peptide hormones involved in a variety of functions ranging from stress response to energy homeostasis. In mammals and fish, the POMC-derived peptide -melanocyte stimulating hormone (MSH) is known to be involved in appetite suppression through its interaction with melanocortin-4 receptors. The details of energy homeostasis in fishes are beginning to be elucidated and many of the genes involved in mammalian neuroendocrine signaling pathways are being discovered in fish. In salmonid fishes such as the rainbow trout, genome duplication adds another degree of complexity when trying to compare gene function and homology with other vertebrates. This is true of the POMC gene. Two copies of the POMC gene were previously identified, A and B, presumably resulting from the salmonid duplication. However, while investigating POMC involvement in the feeding response of rainbow trout, a second copy of POMC-A was discovered which is more likely the result of the salmonid duplication and suggests that POMC-B is a duplicate resulting from the earlier teleost duplication prior to tetrapod divergence. The duplicated POMC-A had five deleted amino acids, five inserted amino acids, and 39 amino acid differences from the published POMC-A. In addition to the duplicate POMC-A, a splice variant of the published POMC-A sequence was also identified. Quantitative real-time PCR assays were developed for the different POMC transcripts, and expression was examined in a variety of tissues. Expression of POMC transcripts was highest in the pituitary for all POMC genes, but varied among other tissues for POMC-A1, POMC-A2, POMC-A2s, and POMC-B. POMC-A1 was the only transcript to respond significantly to food deprivation.

Acute anorexigenic action of leptin in rainbow trout is mediated by the hypothalamic Pi3k pathway

“…The rainbow trout pomc genes are predominantly expressed in the hypothalamus and pituitary gland (Leder & Silverstein 2006), and cells bodies containing Pomc are primarily located in the NLT region and pituitary gland (Suzuki et al 1997, Tollemer et al 1999. Although colocalization of Pomc and LepR L has not been examined in the current study, the presence of LepR L as well as the activation of the Pi3k-Akt pathway by Lep in this region strongly suggests a direct Lep action in Pomc neurons, resulting in the increased expression of the pomca1, pomca2, and pomcb genes by the ICV Lep injection.…”

“…In rainbow trout, npy expression is high in the telencephalon, preoptic area and optic tectum, and relatively lower in the mediobasal hypothalamus (Doyon et al 2003). While the Pomc genes (pomca1, pomca2, pomcb) are highly expressed in the rainbow trout hypothalamus (Leder & Silverstein 2006), and the Pomc cell bodies are found in the NLT region (Suzuki et al 1997, Tollemer et al 1999. Peripheral Lep treatment of rainbow trout has transiently reduced the hypothalamic npy expression levels, while stimulating the expression of pomca1 and pomca2 (Murashita et al 2008), indicating a similar neuropeptide mediation of anorexigenic effects of Lep in fish as in mammals.…”

“…Npy, Agrp, and orexin are major orexigenic peptides expressed in the central nervous system, whereas Pomc, Cart, cholecystokinin (Cck), and corticotropin-releasing factor (Crf) are anorexigenic factors (Jensen et al 2001, Leder & Silverstein 2006, Xu & Volkoff 2007, Murashita et al 2009). The presence of Npy, beta-endorphin, and adrenocorticotropic hormone has been demonstrated in the lateral tuberal hypothalamic region in various fish species (Meek & Nieuwenhuys 1998).…”

Ceramide counteracts the effects of ghrelin on the metabolic control of food intake in rainbow trout

“…Analyses were performed on 1 µl cDNA using MAXIMA SYBR Green qPCR Mastermix (Life Technologies), in a total PCR reaction volume of 15 µl, containing 50-500 nmol l −1 of each primer. mRNA abundance of transcripts was determined as previously described in the same species by Leder and Silverstein (2006;POMCa1) Rolland et al (2015;mTOR). Sequences of the forward and reverse primers used for each gene expression are shown in Table 1.…”

Stress in Atlantic salmon: response to unpredictable chronic stress

“…We analysed the transcript abundance of pomca1 and pomcb1, paralogues that originate from the salmonid genome duplication (Arends et al, 1998;Leder and Silverstein, 2006;Macqueen and Johnston, 2014;Salbert et al, 1992). No changes in pomca1 and pomcb1 mRNA transcripts were observed when fish were subjected to either UCS or the novel stressor.…”