alpha-MSH acetylation in the pituitary gland of the sea bream (Sparus aurata L.) in response to different backgrounds, confinement and air exposure

Abstract

MSH is a pituitary hormone derived by post-translational processing from POMC and involved in stress and background adaptation. N-terminal acetylation of MSH to monoacetyl -MSH or diacetyl -MSH increases the bioactivity of the peptide. The aim of this study was to characterize -MSH acetylation in the sea bream (Sparus aurata L.) pituitary gland in response to the stressors air exposure and confinement, as well as in fish adapted for 15 days to a white, gray or black background. Pituitary homogenates were purified by reversed-phase HPLC (RP-HPLC). The -MSH content of fractions was measured by RIA. Immunoreactive RP-HPLC fractions were further analyzed by electrospray mass spectrometry and the peptide sequence determined as SYSMEHFRWGKPV-NH 2 . In the pituitary gland of sea bream, des-, mono-and diacetyl -MSH were identified. Then plasma -MSH levels were measured in sea bream adapted to different backgrounds. Surprisingly, we found the highest plasma -MSH levels in white-adapted as compared with black-adapted sea bream with intermediate values for gray-adapted fish. This observation is in contrast with results that have been obtained in eel, trout or terrestrial vertebrates. Next, des-, mono-and diacetyl -MSH forms were measured in homogenates of the pituitary gland and in plasma of sea bream exposed to air, to confinement, or to different backgrounds. Monoacetyl -MSH was the predominant form in all control and experimental groups. The lowest content of monoacetyl -MSH relative to des-and diacetyl -MSH was found in white-adapted fish. Levels of des-and diacetyl -MSH forms were similar under all conditions. We observed that monoacetyl -MSH is the most abundant isoform in the pituitary gland after background adaptation, confinement and air exposure, in sea bream. These data indicate that the physiologically most potent isoform of -MSH may vary from species to species.

Characterization of the sea bass melanocortin 5 receptor: a putative role in hepatic lipid metabolism

“…Therefore, acetylation seems to be critical for sbMC5R activation but not the level of acetylation since monoacetyl (-MSH) and diacetyl-MSH were equipotent when activating the receptor. All three MSH isoforms have been described in fish pituitary (Dores et al, 1993) and the regulation of MSH acetylation seems to be an important mechanism for background adaptation and pigment patterns (Arends et al, 2000;Kobayashi et al, 2009). SbMC5R was weakly activated by incubation with human ACTH and -MSH.…”

Background adaptation and water acidification affect pigmentation and stress physiology of tilapia, Oreochromis mossambicus

“…The involvement of aMSH in pigmentation in fish has been reported for several species, such as catfish, eel and trout (Baker et al, 1984), while in arctic charr, flounder, gilthead sea bream and red porgy such an involvement could not be demonstrated (Arends et al, 2000;Baker et al, 1984;Höglund et al, 2002;Salm et al, 2004). Earlier conclusions by Eys and Peters (1981) based on infusion of very high concentrations of exogenous aMSH do not corroborate our findings and we ascribe this to the concentrations used in that study.…”

Handling does not affect reproductive signals of male threespine stickleback

“…Although measurement of signals in the field avoids potential effects of laboratory lighting on signal expression, spectrophotometric techniques still require investigators to capture and handle subjects, an experience that is likely stressful to the animal (Aerends et al 1999(Aerends et al , 2000van der Salm et al 2006). Whereas signal reflectance characteristics of feathers and fur are stable and unaffected by handling stress, signal colour in fish can change rapidly in response to stressful conditions (Green and Baker 1991).…”