Localization and dynamics of Mel 1a melatonin receptor in the ovary of carp Catla catla in relation to serum melatonin levels

Abstract

We studied the localization, sub-cellular distribution and daily rhythms of a 37 kDa melatonin receptor (Mel 1aR) in the ovary to assess its temporal relationship with the serum melatonin levels in four different reproductive phases in carp Catla catla. Our immunocytochemical study accompanied by Western blot analysis of Mel 1aR in the ovary revealed that the expression of this 37-kDa protein was greater in the membrane fraction than in the cytosol. Ovarian Mel 1aR protein peaked at midnight and fell at midday in each reproductive phase. Conversely, serum melatonin levels in the same fish demonstrated a minimum diurnal value at midday in all seasons, but a peak at midnight (during pre-spawning, spawning, and post-spawning phases) or at late dark phase (during preparatory phase). In an annual cycle, band intensity of Mel 1aR protein showed a maximum at night in the spawning phase and a minimum in the post-spawning phase, demonstrating an inverse relationship with the levels of serum melatonin. Our data provide first evidence of the presence of Mel 1a melatonin receptor in carp ovary and offer interesting perspectives especially for the study of the mechanisms of the control of its rhythmicity and its response to external factors.