Meeting Abstract
P2.35 Friday, Jan. 4 cDNA cloning, mRNA expression, and negative feedback regulation of thyrotropin-beta (TSH-β) in the red drum (Sciaenops ocellatus) JONES, R.A.*; COHN, W.B.; VALVERDE, R.A.; LEINER, K.A.; MACKENZIE, D.S.; Texas A&M University; Texas A&M University; Southeastern Louisiana University; Texas A&M University; Texas A&M University rajones@mail.bio.tamu.edu
We report the molecular cloning of the full-length cDNA for thyrotropin-beta subunit (TSH-β) in a perciform fish, the red drum, Sciaenops ocellatus. Comparison of the translated cDNA with known sequences established regions of identity and similarity common to all TSH-βs, and specifically confirmed its closest similarity within vertebrates was to other fishes. A ~600 bp cDNA fragment was used as a probe to detect TSH-β mRNA levels expressed in red drum pituitaries. Northern blots showed a single band similar in size to other TSH-βs. RT-PCR analysis showed tissue specific expression of TSH-β that was readily detectable in pituitaries of both captive and wild animals, but undetectable in other tissues. In vitro incubation of pituitary glands from captive red drum indicated a steady level of expression beyond 24 hours suggesting that TSH-β expression is not inhibited by the hypothalamus. Chronic in vivo administration of the goitrogen methimazole increased TSH-β mRNA levels over controls, while chronic triiodothyronine (T3) administration greatly diminished TSH-β mRNA levels. These results are consistent with the hypothesis that TSH-β mRNA expression is regulated by the negative feedback of circulating thyroid hormones in red drum. Further, these results indicate that TSH-β expression will serve as a useful tool for examining the central regulation of thyroid function in a fish species which exhibits dynamic daily thyroxine cycles.
