Abstract: In order to study the regulation mechanism of TSHB-DIO2/DIO3 system on seasonal breeding of the yak,RT-PCR was used to analyze the cDNA sequences of gene TSHB,DIO2,and DIO3,and the phylogenetic tree was constructed based on the sequences of bovine gene TSHB,DIO2,and DIO3 in the GenBank. Further,their mRNA expression levels in hypothalamus,pituitary,ovary,oviduct and uterus were analyzed by real-time PCR. These results indicated that there was very close evolutionary relationship in yak’s gene TSHB,DIO2,and DIO3 between a yak and a bovine. The coding region of gene TSHB was 417 bp,and its expression level in pituitary was significantly higher than that in other tissues（P < 0.01）. The cDNA sequence of DIO2 gene was 951 bp and expressed in all tissues,but it was significantly higher in the uterus than that in the other four tissues（P < 0.01）. The cDNA sequences of DIO3 gene was 873 bp and was not detected in the uterus,the expression of which in the ovary was significantly higher than that in the pituitary,hypothalamus and oviduct（P < 0.01）. This study suggests that the TSHB-DIO2/DIO3 may be involved in the regulation of yak reproduction,which may provide a reference for preliminarily revealing the molecular regulation mechanism of yak seasonal breeding.

Key words: TSHB, DIO2, DIO3, yak, tissue expression