Some characteristics of soluble thyroid proteins in human fetus during morphogenesis of follicular structure

Soluble thyroid proteins of the human fetus were studied in parallel with the formation of the follicular structure of the gland using polyacrylamide disc electrophoresis and a radioimmunological method for measuring thyroglobulin (Tg). The study covered 24 fetuses obtained after sectio parvae performed at 12-28 weeks of gestation for socio-medical reasons. Before the first trimester of gestation the human fetal thyroid, which did not have an organized follicular structure contained a significant amount of the 12S protein fraction, but only trace amounts of Tg. In the cells of a gland of afollicular structure immunofluorescent material was confirmed by reaction with anti-Tg antibodies. Later, with the formation of follicles and the appearance of follicular colloid, the absolute and relative amounts of Tg in the fetal gland increased, while the 12S subunit decreased. The Tg content in the fetal thyroid was positively correlated with the total weight of the gland, i.e. gestational age. The T4 and T3 contents in Tg of human fetal thyroids (20-24 weeks) amounted to 0.54 +/- 0.39 and 0.12 +/- 0.09 mole/Tg mole, respectively. The 27 S iodoprotein was not found in any of the extracts of fetal thyroids with formed follicles and considerable amounts of follicular colloid. The finding of the 12 S protein in the human thyroid during early fetal life, i.e. in the prefollicular phase, implies a low rate of aggregation of Tg subunits (12 S). The absence of the 27 S iodoprotein from the fetal thyroid with organized follicular structure suggests the yet incomplete morphological and biochemical maturation of the fetal gland.