Melatonin plays an important role in regulating the reproduction of seasonally propagated mammals. Its receptor MTNR1a (Melatonin receptor 1a) is mainly involved in circadian rhythm and reproductive regulation, and MTNR1b (Melatonin receptor 1b) is closely related to a variety of diseases. In order to investigate the biological function of melatonin receptor gene, the expression patterns and localization of MTNR1a and MTNR1b in different yak tissues were clarified in this study. The expression patterns of MTNR1a and MTNR1b in different tissues of adult male yak and in testes at different developmental stages (30 days old, 2, 4, 6 and 8 years old) was detected by qRT- PCR. Furthermore, the MTNR1a and MTNR1b in testes of yaks of different ages were localized by immunohistochemical technique. The results showed that the expression of MTNR1a mRNA was highest in pineal gland, followed by lung, muscle and testis. The expression of MTNR1a mRNA in the testes was gradually increasewith age, and tended to be stable after 4 years old. The MTNR1a protein is expressed in the testis tissue of yak at different developmental stages, and round spermatozoa showed strong immunolocalization, followed by primary spermatocytes. MTNR1a protein was expressed in pineal gland. The expression of MTNR1b mRNA was highest in pineal gland (P<0.05), followed by kidney, liver and hypothalamus. MTNR1b mRNA was expressed in yak testes of different ages, and the expression level increased with age, highest at 8 years old. The

immunohistochemistry result showed that the MTNR1b protein is mainly localized in round spermatids. The extensive expression of MTNR1a and MTNR1b genes in different tissues and testes of yaks at different developmental stages reveals their important roles in male yak reproduction and other physiological processes.

褪黑素对调节季节性繁殖哺乳动物的生殖具有重要调节作用。其受体MTNR1a（Melatonin receptor 1a，褪黑素受体1a）主要参与昼夜节律和生殖调控，MTNR1b（Melatonin receptor 1b，褪黑素受体1b）与多种疾病发生密切相关。为了探讨褪黑素受体基因的生物学功能，本实验对牦牛不同组织中MTNR1a、MTNR1b基因的表达与定位情况进行了研究。采用qRT-PCR (Quantitative Real-Time PCR, qRT-PCR) 检测成年雄性牦牛各组织及不同发育阶段（30日龄，2岁、4岁、6岁和8岁龄）牦牛睾丸组织中MTNR1a、MTNR1b mRNA的表达规律，并运用免疫组化技术对不同年龄牦牛睾丸中MTNR1a、MTNR1b蛋白进行了定位研究。结果发现，MTNR1a mRNA在松果体组织中表达量最高，肺脏、肌肉和睾丸次之；随着年龄增加，MTNR1a mRNA在睾丸中的表达量逐渐升高，到4岁后表达量趋于平稳；MTNR1a蛋白在不同发育阶段牦牛睾丸组织中均有表达，圆形精子呈现较强的免疫阳性，其次为初级精母细胞；MTNR1b mRNA在松果体表达量最高（P<0.05），肾脏、肝脏和下丘脑次之；在不同年龄牦牛睾丸中MTNR1b mRNA均有表达，且随着年龄的增加表达量逐渐增加，在8岁时表达量最高；MTNR1b蛋白主要定位在圆形精子细胞中。MTNR1a、MTNR1b基因在牦牛不同组织及不同发育阶段睾丸中的广泛表达，揭示了其在雄性牦牛生殖等生理过程中的重要作用。