The Thyrotropin β-Subunit Gene Is Repressed by Thyroid Hormone in a Novel Thyrotrope Cell Line, Mouse TαT1 Cells1

TSH is expressed in two populations of thyrotropes in the pituitary: one in the pars distalis and a second in the pars tuberalis. Pars distalis thyrotropes exhibit classical endocrine inhibition of TSH by thyroid hormone, whereas pars tuberalis thyrotropes do not. The majority of our understanding of TSH subunit gene regulation has come from studies conducted in dispersed pituitary, dispersed thyrotropic tumors, or the GH3 somatolactotrope cell line. However, the dispersed pituitary model is limited because of its inherent heterogeneity, thyrotropic tumors are difficult to grow and maintain, and the GH3 cells lack endogenous TSH expression. The recent derivation of a clonal thyrotrope cell line, TαT1, that expresses thyrotrope-specific markers, overcomes these limitations. However, because it was not possible to distinguish whether the tumor from which the TαT1 cells are derived originated in the pars distalis or the pars tuberalis, it was necessary to define their cellular origin and thereby establish th...