Morphogenesis of Thyroid Follicles in Vitro

Material and Methods.- Cultures.- Electron Microscopy.- Results.- I. Freshly Dissociated Cells.- A. The Isolated Cells.- B. The Fragments of the Follicle Epithelium.- II. Unreassociated Cells.- A. Control Cells after 15 min Culture.- B. Control Cells after 4 or More Days in Culture.- III. The Reassociated Cells.- A. Small Aggregates.- B. The Early Follicle.- C Ultrastructural Modifications of the Reassociated Cells.- D. Growth of the Follicle.- E. The Cells Reassociated after Several Days of Culture.- IV. Other Elements in the Culture.- A. The C Cells.- B. Connective Tissue Components.- C. Basal Lamina.- Discussion.- I. Biochemical Aspects of Follicular Reassociation in Cultured Thyroid Cells.- A. Reaggregation of Dissociated Cells: General Review of Known Biological Systems.- 1. The Example of Dictyostelium Discoideum.- 2. Reaggregation Mechanisms.- a) In Dictyostelium Discoideum.- b) In Other Species.- c) The Specificity of Aggregation Promoting Factors.- 3. Mechanisms of Cell Adhesion.- a) In Dictyostelium Discoideum.- b) In Other Species.- B. Reaggregation and Reassociation of Isolated Thyroid Cells.- 1. Analogy with Known Systems.- a) Reaggregation Promoting Factor.- b) Cellular Adhesion and Metabolic Activity.- 2. Role of TSH in Reaggregation and Follicular Reassociation in Vitro.- a) Data from the Literature.- b) Reasons for these Contradictions.- c) Conclusion.- 3. Other Factors that Could Be Responsible for Follicular Morphogenesis in Vitro.- a) Endogenous TSH.- b) 3?-5? Cyclic AMP (cAMP).- c) Other Thyroid Molecules.- d) Connective Tissue Elements.- e) Calf Serum.- 4. Conclusion.- II. Ultrastructural Aspects of Follicular Reassociation.- A. Cells after Trypsinization.- 1. Plasmalemma Modifications.- 2. Cytoplasmic Modifications.- B. Follicular Reassociation.- 1. Reconstitution of the Cell Junctions.- a) Cell Contacts.- b) Zonula Occludens.- c) Adult Junctional Complex.- d) The Problem of Reconstitution of Cell Polarity.- 2. Cytoplasmic and Nuclear Modifications.- 3. Morphogenesis of the Microvilli.- 4. Nature of the Dense Follicular Material.- a) Ultimobranchial Colloid.- b) Immature Thyroglobulin.- c) Thyroglobulin Modified by the Processing for Electron Microscopy.- d) Cell Catabolism Products.- e) Membrane Glycoproteins or “Cell Coat”.- 5. Morphogenesis of Cilia.- 6. Growth of the Follicle.- 7. The Role of Hydrocortisone.- III. The Origin of the Follicular Lumen.- A. Hypothesis for the Formation of the Follicular Lumen from Intracytoplasmic Cavities.- 1. Review of the Work by Light Microscopy.- 2. Review of the Work in Electron Microscopy.- B. Hypothesis of the Formation of the Follicular Lumen from the Intercellular Space Partitioned by an Annular Zonula Occludens.- 1. Review of the Literature.- 2. Proofs Supporting this Hypothesis.- a) Study of Ultrathin Serial Sections.- b) Study of Follicular Models (Figure 15).- IV. Comparative Arguments Supporting the Extracellular Origin of the Follicular Lumen.- A. Phylogenic Development of the Thyroid Gland.- 1. Formation and Histology of the Lamprey Endostyle (Subpharyngeal Gland).- 2. Appearance of the Thyroid Gland.- B. General Cytologic Aspects of Differentiation of Epithelia.- 1. Data Relevant to the Problem.- 2. Reaggregation of Dissociated Embryonic Cells.- 3. Development of the Blood Capillaries.- 4. Morphogenesis of Kidney Glomeruli and Tubules.- 5. Organogenesis and Histogenesis of the Pancreas.- 6. Morphogenesis of the Biliary Canaliculi of the Liver Parenchyme.- 7. Development of Gastric Oxyntic Cells.- 8. Conclusion.- Summary.- Acknowledgements.- References.