Helical Structures in the Nucleus of Amoeba proteus

While Amoeba proteus has long been the subject of extensive cytological and cytochemical studies, investigations with the electron microscope have been limited principally to the nuclear membrane (1-3). The observations reported herein were made in the course of studies intended to correlate cytochemistry (4) with knowledge of fine structure obtained with the electron microscope. I t is felt that the unique character of these observations justifies this brief note, The amebas were first washed free of other protozoa, and then fixed with 1 per cent OsO4 in a veronal-acetate buffer~ pH 8.6, containing 0.01 per cent CaCI~. Fixation time varied from 10 to 20 minutes. After dehydration :and embedding in n-butyl methacrylate, thin sections were cut and subsequently studied in the electron microscope (RCA, EMU-2E). The characteristic nuclear structure is seen in Fig. 1. Just within the unusually thick and complex nuclear membrane (NM) are numerous dense bodies (D) which range from 0.4 to 1.7 g in size. Such bodies, as described by Chalkley (5), stain intensely with hematoxylin but are Feulgen-negative. The more interior regions of the nucleus, beyond these peripheral bodies, show a diffusely Feulgen-positive reaction. In these regions, we have found clumps of helical structures. These helices are single and not paired. I t is difficult to trace their origins. The longest spirals are between 2500 and 3000 A in length and radiate irregularly from a diffuse central region