Abstract Thyroid stimulating hormone (TSH) is a glycoprotein hormone consisting of an α and a β chain. Within the hypothalamus-pituitary-thyroid axis, TSH is produced by thyrotropic cells in the anterior pituitary. Upon release into the circulation, TSH binds to receptors in the thyroid, resulting in the release of triiodothyronine (T3) and thyroxine (T4). T3 and T4 regulate nearly every aspect of mammalian physiology, including basal metabolism, growth and development, mood, and cognition. Although TSHβ has been known for years to be produced by cells of the immune system, the functional significance of that has remained unclear. My laboratory identified a splice variant of human TSHβ (TSHβv) that consists of a truncated but biologically active portion of TSHβ made from exon 3 with the deletion of exon 2. The signal peptide of TSHβv is coded for by a portion of the 3′ end of intron 2. TSHβv is primarily produced by bone marrow cells and peripheral blood leukocytes, particularly though not exclusively by cells of the myeloid/monocyte lineage. An unresolved question pertains to the molecular mechanisms that account for TSHβv alternative splicing, Here, a model is presented whereby TSHβv is made through a series of unique genetic reorganization steps. These findings have implications not only for understanding how the TSHβv isoform is made, but also for gaining insights into the involvement of immune system TSHβ in health and disease.
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