Immunofluorescent study of thyroglobulin during development of embryonic thyroid gland function

The synthesis of the protein component of thyroglobulin was studies by the method of immunofluorescence in the thyroid glands of rat, guinea pig, chicken, and calf embryos. Diffuse specific fluorescence of the cytoplasm was observed in the prefollicular stage of thyroid gland differentiation. It was assumed that the specific fluorescence is due to low molecular weight precursors of thyroglobulin. During the formation of the follicles specific fluorescence is found at the apical poles of the cells and later it is concentrated at the cell-colloid boundary and in the follicular cavity. In calf fetuses in the second half of embryonic development specific fluorescence is observed in addition in the cytoplasm of the follicular cells.