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Title

The stress system in Solea senegalensis: molecular and physiological approaches

AuthorsWunderink, Yvette S.; Engels, Steef; Halm, Silke ; Yúfera, Manuel ; Martínez-Rodríguez, Gonzalo ; Flik, Gert; Klaren, Peter H. M.; Mancera, Juan Miguel
Issue DateApr-2011
CitationV Workshop The cultivation of the Soles (2011)
AbstractThe hypothalamus-pituitary-interrenal (HPI) axis is pivotal in the adaptive stress response of fish. Hypothalamic corticotropin-releasing hormone (CRH) initiates the endocrine stress response and stimulates the release of adrenocorticotropic hormone (ACTH) from the pituitary pars distalis. ACTH activates the interrenal cells of the head kidney to produce and release cortisol, which is the main stress steroid. Together with other peptides like MSH and ß-endorphin, ACTH derives from the precursor protein proopiomelanocortin (POMC) by post-translational cleavage. CRH activity is regulated by a specific CRH binding protein (CRH-BP), which is generally considered to be a potent antagonist of CRH. Chronic exposure to stressors can lead to allostatic overload, which negatively affects reproduction, growth and immune functions leading to diseases and reduced animal welfare. Considering plasma cortisol levels in fish as readout for stress, increased stocking density (a typical situation in aquaculture activity) is known to evoke crowding stress. However, the precise role of the central HPI axis has not yet been established. Furthermore, fish in aquaculture must cope with exposure to a series of acute stressors such as transport, weighing, sorting/grading and sudden environmental changes e.g. in food availability, water temperature and salinity. Proceeding from this notion, we developed new tools at molecular level (characterization of the cDNAs coding for S. senegalensis CRH, CRH-BP and two forms of POMC) and investigated their roles in relation to a chronic stressor (viz. increased stocking density) and the ability to cope with a subsequent acute stressor (viz. transfer to increased ambient salinity). Therefore, juveniles were kept at three densities (1.9, 4.7 and 9.8 kg/m2) for 33 days, and then transferred from seawater (SW, 39¿ salinity) to high salinity seawater (HSW, 55¿). The highest density imposed stress as indicated by elevated cortisol levels and CRH mRNA expression, compared to fish kept at low density. Fish kept at high density responded differently to a posterior transfer to HSW showing no cortisol or CRH response, but osmoregulatory and metabolic parameters were affected. These results indicate a compromised capacity to cope with a subsequent acute stressor, which might implicate that S. senegalensis does not adapt successfully to high stocking density. No differences in CRH-BP mRNA expression levels were found at different stocking densities but transfer to HSW enhanced expression in both low and high density stocked fish, suggesting that CRH-BP acts as a modulator of the acute stress response under our experimental conditions. As for POMC, two transcripts were found, most likely presenting subfunction partitioning between the paralogues: S. senegalensis POMC ¿A¿ shows a high homology of 98% identity with S. solea POMC, but cannot cleave to ACTH and completely lacks the opioid consensus in the ß-endorphin part. POMC ¿B¿, however, lacks the N-terminal cleavage site for ß-MSH. Furthermore, ß-endorphin derived from POMC A seems to be under neutral evolution, whereas POMC B possesses well-conserved peptide regions under strong purifying selection. Also, differential mRNA expression was seen between POMC A and B, suggesting different physiological roles, which will be further investigated. When investigating POMC mRNA expression in the Solea stress system, we recommend keeping in mind POMC¿s structure in order for correct interpretation.
DescriptionTrabajo presentado en el V Workshop The cultivation of the Soles, celebrado en Faro (Portugal) del 5 al 7 de abril de 2011.
URIhttp://hdl.handle.net/10261/104139
Appears in Collections:(ICMAN) Comunicaciones congresos
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