In this thesis we tried to clarify the role of the chicken thyrotropin receptor (cTSHR) and thyroid hormone receptor β2 (TRβ2) in the feedforward and feedback interactions within the hypothalamo-pituitary thyroidal axis (HPT). As the activity of the HPT alters during late embryogenesis and perinatal period, we examined whether both receptor types participate in adjusting thyroid hormone (TH) concentrations during this critical developmental period.
First, we have cloned and functionally characterized the chicken TSHR and detected cTSHR mRNA in various extra-thyroidal tissues such as pituitary gland and diencephalon, two major control levels of the HPT. Next to the full-length receptor, 2 N-terminal and 3 C-terminal variants were discovered but whether they are actually translated into proteins still needs to be verified. Furthermore, by measuring the thyroidal cTSHR mRNA expression towards hatching with real-time PCR we found that the thyroid gland does not become more sensitive for TSH stimulation as relative cTSHR mRNA levels did not change during this developmental period. Other factors such as an elevated feedforward stimulation are more likely candidates for increasing the thyroxine (T4) levels during late embryogenesis. Combined