Pathways of Endocytosis in Thyroid Follicle Cells

Abstract

Publisher Summary This chapter discusses that the thyroid gland maintains constant levels of thyroid hormones, thyroxine and triiodo thyronine, in the circulation of most mammalian species. This ability of the thyroid gland is based on the highly regulated sequence of steps in the secretory process: Thyroglobulin, the macromolecular secretory product, and the precursor of thyroid hormones, is released and stored in the follicle lumen where it remains segregated from the extrafollicular space by a tight epithelial monolayer. Studies on endocytosis in thyroid follicle cells require experimental access to the luminal cell surface. This has been accomplished in the past by microinjection of tracers into the follicle lumen. The chapter discusses that suspensions of inside-out follicles were used in which the apical plasma membranes of follicle cells were directed toward the culture medium and separated by tight junctions from the lateral cell surfaces. The tightness of the epithelial monolayer and the stable inside-out polarity are prerequisites to study endocytosis selectively from the apical plasma membrane. The chapter describes the pathways of endocytosis in thyroid follicle cells with particular reference to results obtained from work with inside-out follicles.