Afrikander cattle congenital goiter: characteristics of its morphology and iodoprotein pattern.

The morphology and some properties of the complex iodoprotein pattern of the genetically determined congenital goiter in Afrikander cattle is described. The goiter contained irregularly shaped follicles which were devoid of colloid and the follicular epithelial cells were elongated, measuring about 20 micrometer in length compared to 10 micrometer for normal thyroid cells. The goiter cells contained apical clusters of larger and more numerous lysosomes than normal thyroid cells. Apical vesicles containing electron-dense material which were in contact with the plasma membrane could be seen in most normal thyroid cells, but were extremely scarce in the goiter. In 36 cell profiles studied none was found. The endoplasmic reticulum cisternae of the goiter differed significantly from normal thyroid cells. Fewer ribosomes were seen to be attached to the membranes of goiter cells. Furthermore, unlike normal thyroid cells, many free polysomes were seen in goiter cells. The characteristics of the unusual iodoprotein pattern of the goiter extract, resolved by gel chromatography and sucrose density gradient centrifugation, were qualitatively and quantitatively similar to that described previously (Endocrinology 91, 470, 1972). A relatively small amount of the total soluble protein was iodinated. Of these, only a 12S sedimenting species was precipitated by antithyroglobulin immunoglobulin. When separated on polyacrylamide gels containing sodium dodecyl sulfate and mercaptoethanol, this 12S species was resolved into at least 14 polypeptide components ranging in molecular weights from less than 66,000--330,000. Three of the bands, representing a small percentage of the total protein, seemed to comigrate with the major polypeptides of thyroglobulin and were also precipitated with rabbit antihyroglobulin immunoglobulin. The data indicate that glycosylation of iodoproteins was not affected although 19S thyroglobulin synthesis and subsequent storage were drastically impaired.