Regulation of growth hormone expression by thyrotropin-releasing hormone through the pituitary-specific transcription factor Pit-1 in chicken pituitary.
Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone beta- (TSHbeta) encoding genes. Pit-1 has been identified in several mammalian and avian species. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and it stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully developed a competitive RT-PCR for the detection of Pit-1 expression in the chicken pituitary, that was sensitive enough to detect picogram levels of Pit-1 mRNA. Applying this method, the effect of TRH injections on Pit-1 mRNA expression was determined in the pituitary of chick embryos and growing chicks. In both 18-day-old embryos and 10-day-old male chicks the Pit-1 mRNA expression was significantly increased following TRH injection, thereby indicating that the stimulatory effects of TRH on several pituitary hormones is mediated via its effect on Pit-1 expression. Therefore, a semi-quantitative RT-PCR method was used to detect possible changes in GH levels. TRH affected the GH mRNA levels at both developmental stages. These results, combined with the data on Pit-1 mRNA expression, indicate that Pit-1 has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH.
Van As
P
P
Laboratory for Physiology and Immunology of Domestic Animals, Department of Animal Production, Katholieke Universiteit Leuven, Kasteelpark Arenberg 30, B-3001 Leuven, Belgium. pieter.vanas@agr.kuleuven.ac.be
Careghi
C
C
Bruggeman
V
V
Onagbesan
O M
OM
Van der Geyten
S
S
Darras
V M
VM
Decuypere
E
E
D000818:Animals; D002642:Chick Embryo / Q000378:metabolism; D002645:Chickens / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D013006:Growth Hormone / Q000096:biosynthesis*; D008297:Male; D009154:Mutation; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods / Q000662:veterinary; D012680:Sensitivity and Specificity; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology / Q000502:physiology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000502:physiology*
D012333:RNA, Messenger; D014157:Transcription Factors; D013973:Thyrotropin-Releasing Hormone; D013006:Growth Hormone