Expression profile of thyroid hormone deiodinases in the adult laying hen (Gallus gallus domesticus)

In this study, the mRNA expression of three deiodinases (DIO1, DIO2, and DIO3) was investigated in adult (96-week-old) female chicken tissues by using real-time quantitative PCR and specific TaqMan probes. The analysis included the hypothalamus, pituitary gland, thyroid gland, lungs, heart, stomach, small intestine, spleen, pancreas, skeletal muscle, adipose tissue, skin, and reproductive system (RS). Within the RS, deiodinase expression was measured in all oviductal segments (infundibulum, magnum, isthmus, shell gland, and vagina) and the prehierarchical (small [SWF] and large white follicles [LWF]) and preovulatory (F3, F2, and F1) ovarian follicles, with separate analyses for the theca and granulosa layers. The three deiodinases were present in all tissues. Compared to control thyroid tissue, the highest expression of DIO1 was in the liver, followed by the kidney and small intestine. DIO2 exhibited the most significant expression levels in the liver and pituitary gland. The most outstanding result was the extremely high expression of DIO3 in the ovary, with the maximal level in the granulosa layer of preovulatory follicles, followed by the theca layers and the prehierarchical follicles. The expression profiles of deiodinases in adult chicken hens are highly tissue-specific, reflecting the diverse physiological roles of thyroid hormones in these tissues. The exceptionally high expression of DIO3 in the ovary, particularly in the granulosa layer, indicates an essential role of this enzyme in maintaining an appropriate 3,3',5-triiodothyronine (T3) concentration for follicular development and its participation in protection against excessive transfer of maternal T3 to the oocyte yolk.