Effects of dissociating agents on the fine structure of embryonic chick thyroid cells

The processes of dissociation and reaggregation were studied in thyroids from 16‐day chick embryos by means of electron microscopy. The purpose was to gain specific knowledge of the effects that dissociating agents have upon cells. Fixation after a soak in trypsin showed little effect on secretory cell structure but resulted in marked swelling and detachment of connective tissue elements and disorganization of the basement lamella of the follicles. After an additional exposure to ethylenediaminetetraacetate (EDTA), however, the channels of the endoplasmic reticulum and the Golgi vesicles became swollen and separations appeared between adjacent secretory cells. Since detachment did not occur in the region of the junctional complex, agitation was required to achieve suspension of the cells. Even this treatment resulted in only a small proportion of individual cells, the majority being in the form of small clumps or chains. Transfer of the suspensions to nutrient medium and reaggregation produced pellets which rapidly formed follicles in organ cultures. The individual cells showed the same degree of complexity as in follicles in vivo . The results are related to the known effects of trypsin and EDTA on cells. The significance of morphogenesis in aggregates prepared from cells of older embryonic organs is also discussed.