Abstract: Melatonin is an indole hormone secreted by the pineal gland， and involved in regulating the circadian， seasonal reproduction， antioxidant activity and antiapoptosis. The present study investigated the expression， distribution and relative expression quantity of Mel1a mRNA and Mel1a protein in different organs of duck， which laid the foundation for further study on regulating effect of melatonin on the reproductive physiology and other biological function. In this study， we collected the heart， spleen， brain， cerebellum， kidney， liver， lung， ovary， pancreas and muscle tissues of duck. The expression of Mel1a in duck tissues were detected by the methods of PCR and immunohistochemical techniques at mRNA and protein levels. The Mel1a mRNA relative expression quantities in different organs were detected by realtime PCR. The major results were described as follows: Mel1a mRNA was expressed in the heart， spleen， brain， cerebellum， kidney， liver， lung， ovary， pancreas and muscle tissues of duck. Mel1a protein was expressed in the brain， lung， liver， muscle， kidney， heart and pancreas tissues of duck. Moreover， realtime quantitative PCR was used to detect the relative expression level of Mel1a gene in different tissues and the gene expression level in brain was selected as a baseline. The quantitative results showed that Mel1a gene had high expression levels in brain， lung， ovary， spleen， cerebellum and pancreas and low levels in kidney， liver， muscle and heart. Melatonin plays an important role in physiological regulation function by binding to its receptors and it is very important to study the melatonin receptor expression and distribution， which are useful to elucidate the role and mechanism of melatonin on circadian rhythm， antiapoptosis， antioxidant activity， enhancing immunity， oocyte maturation and embryo development.

Key words: duck, Mel1a, immunohistochemistry, tissue expression, fluorescent quantitative PCR