Helical inclusions with nucleopore-like characteristics in the cytoplasm of Swiss 3T3 cells: a preliminary communication.

Helical inclusions have been observed at sites remote from the nucleus in the cytoplasm of Swiss 3T3 fibroblasts. Because of the interest shown in their unusual nucleopore complex-like nature, this preliminary communication briefly reports their existence and describes their essential ultrastructural features. Although they could be found singly, most formed collections of up to about 30 inclusions in which different planes of section were represented. TS profiles with hexagonal packing showed apparently identical eight-fold symmetry and dimensions to pores in the nuclear envelope of 3T3 cells. No membranes were associated with the inclusions, nor was there any suggestion of the strict vertical plate-like stacking found in annulate lamellae (AL). Furthermore, the inclusions were undoubtedly helical, and in all probability composed of several strands.