Fine structures of the thyroid gland in the aged central myelin deficient jimpy mouse.

Abstract

The thyroid glands of 19-25 days old hypomyelinated jimpy mice were embedded in Araldite for morphological studies. The fine structures of the thyroid follicular epithelial cells were characterized by numerous microvilli, well developed rough endoplasmic reticulum with dilated cisternae, large and variously shaped mitochondria , groups of Golgi complex and abundant dense-cored vesides, bizzare shaped pseudopodos and many reabsorbed colloid droplets, and a large nucleus with abundant nuclear pore complex. Occasionally, cilia protruded from the apical surface of epithelial cells into the follicular lumen. In addition , mito-chondria-rich cells, clear cells (c-cells) , ergastoplasm-rich cells, and fenestrated intraepithelial capillaries were found on the follicular wall. Among thyroid foilicles, some incompletely differentiated epithelial masses appeared, which were composed of microfollicular epithelial cells, active mitotic epithelial cells , and small follides. These components were characteristic structures of the early embryonic development and represented the active proliferating stage of folliculogenesis. There were three types of cells observed on the wall of well de-veloped ultimobranchial cysts; i.e., secondary follide cells,c-cells , and ciliated cells. The presence of cysts implicated the underdevelopment of thyroid follicles which normally compressed and inhibited the persistence of ultimobranchial cysts . The evidence presented here proves that the hypomyelination of jimpy mice may be induced by the under - development of their thyroid glands and jimpy genes.