SIALYLTRANSFERASE MESSENGER-RIBONUCLEIC-ACID INCREASES IN THYROTROPHS OF HYPOTHYROID MICE - AN IN-SITU HYBRIDIZATION STUDY

Hypothyroid patients and mice have been shown to have circulating TSH that is more highly sialylated than their euthyroid counterparts. To learn about the underlying cellular mechanisms responsible for this increased sialylation of TSH, we used in situ hybridization to examine the beta-galactoside alpha-2,6-sialyltransferase (STase) mRNA content in thyrotrophs and corticotrophs of euthyroid and hypothyroid mice. Mice were treated with or without 0.05% propylthiouracil for 1, 2, 3, 4, or 6 weeks, then pituitaries were removed, and 5-mu m slices were immunocytochemically stained for TSH and ACTH. Adjacent sections were used for in situ hybridization. A 48-mer deoxynucleotide probe to rat STase and two control probes were labeled with S-35, and autoradiography was performed. There was an approximately 140% increase in STase mRNA in hypothyroid thyrotrophs compared to euthyroid thyrotrophs by the first week, with a mean increase of 170% in weeks 1-6, whereas corticotrophs exhibited no change in STase mRNA. The increase in hybridization of the STase probe in hypothyroid thyrotrophs may be due to an increased transcription of the STase gene, stabilization of the STase mRNA, or both. Thus, modulation of the STase mRNA levels occurs in thyrotrophs and represents one important mechanism by which the oligosaccharides of TSH are altered under different physiological conditions.