Epidermal growth factor stimulates thyroid follicle neogenesis in collagen gel culture

The mechanism involved in the neoformation of thyroid follicles is poorly understood. In the present study, whole porcine thyroid follicles were cultured as "miniorgans", embedded within collagen gels. Incubation was performed up to 4 days with or without EGF (10 ng/ml) and TSH (2 mU/ml). A single dose of 3H-thymidine was added at the start of the experiments in some cases. Light microscopy and autoradiography was performed. EGF induced a dramatic migration of follicles cells; these were seen to back out from the mother follicle and formed microfollicles with normal polarity including microvilli at the apical border. As evident from the analysis of 3H-thymidine incorporation, most microfollicles were comprised of newly divided cells. The results infer a new mechanism for the neoformation of follicles in the thyroid.