Molecular characterization and expression patterns of Atlantic bluefin tuna (Tunnus thynnus) leptin during the reproductive season.

The wide spectrum of tissues expressing the bftLep gene may suggest the hormone's multiple physiological functions in BFT. The mechanisms by which leptin regulates reproductive functions are not yet fully understood. However, the fact that leptin is being produced in the central nervous system (hypothalamus and pituitary) may suggest autocrine and/or paracrine regulation of the hypothalamic-pituitary-gonadal axis. Our striking findings that reveals a clear association between regressed gonads, depleted energy resources (as indicated by the low HIS and FSI values) and increased transcription of the bftLep gene in the hypothalamic tissue, further attest to this notion. Nevertheless, since expression levels do not necessarily mirror the circulating hormone levels, further studies employing homologous immunoassays, are required to clarify the specific physiological roles of leptin in the control of gonadal function in BFT.