Abstract：As we all known, the availability of thyroid hormone within the hypothalamus is a key determinant of seasonal transitions and they convert between bioactive and inactivating type through catalyzing by type Ⅱ iodothyronine deiodinase(DIO2) and type Ⅲ iodothyronine deiodinase(DIO3). So far, many previous studies has revealed that DIO2 and DIO3 genes might regulate seasonal reproduction in rodents (Rodentia) and sheep (Ovis aries), but it is not clear in regulation of goat seasonality. To determine the roles of the 2 genes in goat (Capra hircus) seasonal reproduction, their spatial expression profiles and the differences of expression levels in hypothalamic-pituitary-gonadal axis were analyzed between Jining Grey goat (year-round estrus) and Liaoning Cashmere goat (seasonal estrus) by using RT-PCR and Real-time quantitative PCR methods, respectively. The results showed that (1) DIO2 mRNA expressed in almost all tissues studied, while DIO3 mRNA was mainly found in goat hypothalamus, pituitary, cerebellum, hippocampus, pons, and it was also determined in ovary, adrenal gland and slightly expression in goat spleen, both gene were with similar tissue profiles between two goat breeds except a small quantity of DIO3 expression in cerebral cortex in Liaoning cashmere goat. (2) DIO2 was found in all of 4 tissues detected which related to reproductive regulation and in Jining Grey goat, it expressed higher in pituitary than other tissues (P＜0.05). For Liaoning Cashmere goat, the expressions were significant different among 4 tissues except between hypothalamus and pituitary. DIO2 mRNA expression was higher in pituitary for Jining Grey than Liaoning Cashmere goat (P＜0.05), while that was lower in uterus than Liaoning Cashmere goat (P＜0.05) and without obvious difference in ovary and hypothalamus between 2 breeds even it appeared higher levels in Jining Grey goat (P＞0.05). (3) In Jining Grey goat, the expression of DIO3 was the highest (P＜0.05) in hypothalamus among 4 tissues studied and uterus was detected no DIO3 mRNA. As for Liaoning Cashmere goat, DIO3 expressed the highest in ovary (P＜0.05), then hypothalamus and pituitary, at last lowest in uterus. The level of DIO3 mRNA was lower in ovary and uterus of Jining Grey compared to Liaoning Cashmere goat (P＜0.05), while its expression in hypothalamus was opposite (P＜0.05) and there was no difference in pituitary between these 2 breeds (P＞0.05). The results hinted that DIO2 and DIO3 genes might be related to regulation of seasonal reproduction in goats, which provides reference for preliminarily revealing the molecular regulatory mechanism in goat reproductive seasonality.
