In Vitro Effects of Thyroid-Stimulating Hormone on Total and Polysomal Ribonucleic Acid Synthesis in Monolayer Cultures of Sheep Thyroid Cells*

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Abstract
The effects of TSH on total cell RNA and polysomal RNA from monolayer cultures of sheep thyroid gland cells were investigated. The cells were dispersed from their glandular matrix with collagenase and subsequently cultured at high cell densities. A small transient increase in the incorporation of [3H]uridine into total cellular RNA was observed 1 h after TSH addition to the cultures. TSH addition also resulted in a 1.3- to 2.6-fold increase in the incorporation of either [3H]uridine or [3H]adenosine into the total polysomal RNA prepared from the postnuclear supernatant of detergent-lysed cells. Oligo(dT)-cellulose chromatography was used to fractionate polysomal RNA into poly (A)-containing and poly(A)-lacking classes. TSH increased the labeling but not the size distribution of RNA in the poly (A)-lacking class (mostly ribosomal RNA). However, the poly(A)-containing RNA molecules (mRNA) from TSH-treated cells were not only more heavily labeled, but the size distribution of these labeled molecules, as determined by sucrose density gradient sedimentation, was markedly larger than that of molecules from control cells. The effects of TSH on the increased incorporation of labeled nucleosides into thyroid cell RNA were observed 1) providing the cells were first preincubated for 48 h in the absence of exogeneous TSH, 2) after correcting for changes in the activity of the acid-soluble fractions, and 3) without significant changes in the total cellular contents of RNA or DNA. These results further support the concept of an effect of TSH on transcriptional and posttranscriptional events in thyroid cells in culture.