The role of melatonin on zebrafish follicle development: An FT-IR imaging approach

Melatonin is an important hormone for the synchronization of the reproductive response to appropriate environmental conditions in photoperiodic animals. Even if a large amount of scientific evidences supports its positive impact on oocyte quality and fertilization rate, the biochemical processes involved are not completely understood. Fourier transform infrared (FT-IR) imaging technique has been applied to analyze the variations induced by melatonin administration on both growth and maturation phases of zebrafish oocytes. Chemical maps were acquired on thin ovary sections, from which average spectra were extracted for each class of oocytes. All average spectra were submitted to multivariate analysis, that separated them into different clusters according to oocyte class and treatment. The vibrational analysis highlighted modifications both in the proteic pattern, with an increment in helical structures with respect to β-sheets (amide I and II bands), and in the aliphatic chains and phosphate moieties for oocytes deriving from melatonin treated females. In addition, real time-PCR and enzyme-linked immunosorbent assay (ELISA) analyses showed that the administration of this hormone favoured the synthesis of vitellogenin. The reduction in gene expression involved in preventing oocyte maturation, such as bone morphogenetic protein (bmp15) and transforming growth factor (tgfβ1), was also observed together with the increase of the luteinizing hormone receptor (lhr), involved in the induction of oocyte maturation.