Immunocytochemical study of localization and traffic of thyroid peroxidase/microsomal antigen.

We studied the distribution of binding sites for anti-peroxidase monoclonal antibody and anti-microsomal antibodies on isolated human thyroid follicles and a human thyroid cell line. Both open follicles and cells were incubated first with antibodies at +4 degrees C, then with colloidal gold labelled protein A. The topography of the binding sites for monoclonal anti-peroxidase antibody corresponded closely to the expected cell surface distribution of endogenous thyroid peroxidase since labelling was observed at the apical cell surface of the follicles.

Forskolin stimulates cAMP production and the onset of the functional differentiation in the fetal rat thyroid in vitro.

Forskolin, a diterpen stimulating the adenylcyclase induces in vitro an accumulation of cAMP in thyroid glands explanted from 17 day-old rat fetuses. Thyroid glands from 15 day-old fetuses exposed to forskolin exhibit, within 24 hr, an active folliculogenesis and 125I fixation in follicular cavities. The results indicate that cAMP probably activates the onset of both morphological and physiological maturation in the fetal rat thyroid.

Evidence for a role of the cytoskeleton in the in vitro folliculogenesis of the thyroid gland of the fetal rat.

Thyrotropic hormone (TSH) or cAMP accelerate the formation of follicular cavities in the explanted thyroid gland of the 15-day-old rat fetus. Cytochalasin B or vinblastine and nocodazole or colchicine, which disorganize microfilamental and microtubular structures respectively, inhibit or completely block in vitro-induced folliculogenesis. Exposure of the thyroid tissue to lumicolchicine, a structural isomer of colchicine deprived of antimicrotubular activity, does not inhibit the activation of folliculogenesis induced by TSH.

Thyroid follicular morphogenesis mechanism: organ culture of the fetal gland as an experimental approach.

The morphological and physiological changes induced by organ culture and thyroid-stimulating hormone (TSH) stimulation in the rat fetal thyroid gland were studied. Organ culture increased Golgi activity which was further enhanced by TSH, subsequently facilitating the formation of intracellular lumina. TSH also raised the intracellular cAMP level.

Basement membrane maintenance in cultures of isolated thyroid follicles.

Follicles from adult rat thyroid glands were isolated by digestion with collagenase followed by sieving. Electron microscopic studies have shown that basement membrane was present around each one of the isolated follicles. Follicles were cultured in vitro with or without thyrotropin and fibronectin.

Development of the thyroid gland in the rat fetus in vivo. An ultrastructural and radioautographic study.

A study of the differentiation of the thyroid follicles was carried out in rat fetuses between day 14 of pregnancy, when cellular polarization begins and day 18, when completely formed follicular lumina are differentiated. After day 18, only the shape and the size of the lumina undergo modifications. The mechanism of folliculogenesis involves the participation of several structures.

Critical study of endogenous peroxidase activity: its role in the morphofunctional setting of the thyroid follicle in the rat fetus.

Endogenous peroxidase is associated with thyroglobulin iodination. It first appears at 17 day of pregnancy in rat fetal thyroid and seems to be synthesized within the perinuclear cistern and the rough endoplasmic reticulum. Then, the enzyme is transferred by vesicles up to the follicular lumen where thyroglobulin iodination takes place.

[Critical study of extra-lysosomal acid phosphatase localizations in thyroid follicular cells by the Gomori reaction (author's transl)].

With the Gömöri technique, lead precipitates have been found in thyroid follicle cells in unusual localizations such as apical hyaloplasm and microvilli; it has been established that they were actually significant for acid phosphatase activity: constant results in spite of repeated controls and several variations from the original cytochemical technique, allow to think that lead precipitates were not merely artefactual, but actually significant of enzymatic activity. However it is pointed to the fact that the origin of the enzyme has to be questioned; it is assumed that most likely acid phosphatase has diffused from its original lysosomal site. Such diffusion implies variations of the selective permeability of lysosomal membranes; inappropriate relation between the quantity of enzyme present in these organelles and the quantity of substrate used might also be considered, though changes in the amount (resp.