Nucleolus-like Inclusions in the Cytoplasm of HeLa Cells treated with Puromycin

Neuronal changes induced by neonatal hypothyroidism: an ultrastructural study

The postnatal development of the neurons of the cuneate nucleus was examined ultrastructurally in euthyroid and hypothyroid rats from birth to the sixth postnatal week. In the euthyroid animals, the neurons at birth displayed mild nuclear invaginations and a scanty cytoplasm with few organelles. By 2 weeks, there was a considerable increase in Nissl bodies. At 3 weeks, the neurons contained short lamellar arrays of endoplasmic reticulum. Between 3 and 6 weeks there was a reduction in the Nissl substance. In the hypothyroid animals, although the sequence of maturational changes generally resembled that of the controls, a number of differences were noted. The neurons at 1 week displayed dilations of perinuclear space, rough endoplasmic reticulum, Golgi complexes, and mitochondria. At 4 weeks both perikaryon and myelinated axons contained glycogen. Several neurons with cytoplasmic inclusions considered to be nonfunctional RNA were seen. The 6-week hypothyroid neuron exhibited large, clear, cytoplasmic vacuoles associated with a drastic reduction in cytoplasmic organelles. Presynaptic terminals showed a 50% reduction in mitochondrial numbers associated with the presence of glycogen granules. Three changes observed in neurites in all the age groups included: (1) large accumulation of glycogen in presynaptic terminals; (2) clear vacuoles; and (3) the presence of numerous lamellar bodies within reactive axons. Aberrant myelination, such as a single myelin sheath enclosing multiple processes, and instances of collapsed and redundant myelin were encountered.

The fine structure of puromycin-induced changes in mouse entorhinal cortex

Bitemporal intracerebral injections of puromycin in mice suppress indefinitely expression of memory of avoidance-discrimination learning. Ultrastructural studies of the entorhinal cortex of puromycin-treated mice revealed the following: (a) Abnormalities were not observed in presynaptic terminals and synaptic clefts; many postsynaptic dendrites or somas contained swollen mitochondria. (b) Dispersion of polyribosomes into single units or condensation of ribosomes into irregular aggregates with loss of "distinctiveness" was noted in a few neurons 7-27 hr after puromycin treatment. (c) Cytoplasmic aggregates of granular or amorphous material were frequently noted within otherwise normal neuronal perikarya. (d) Mitochondria in many neuronal perikarya and dendrites were swollen. Mitochondria in axons, presynaptic terminals, and glial cells were unaltered. The relationships between these lesions and the effect of puromycin on protein synthesis and memory are examined. It is suggested that the disaggregation of polysomes is too limited to explain the effect of puromycin on memory. Special emphasis is given to the swelling of mitochondria. The possible mechanisms and the significance of this lesion are discussed.

Persistence of nucleoli in short term and long term cell cultures and in direct bone marrow preparations in mammalian materials

Persistent nucleoli were studied in Chinese hamster and human long term cultures, human peripheral blood short term cultures, as well as direct bone marrow preparations. No colchicine or hypotonic treatments were applied and the cells were differentially stained with the Feulgen method and light green. Nucleoli were found to persist in the three systems studied, although to a much greater extent in the long term culture. The persistent nucleolar materials were usually in the form of individualized nucleoli mainly at chromosome ends. They also sometimes existed in a fluidlike or dropletlike condition around the chromosomes. Association of acrocentrics in humans and end-to-end associations in hamsters are likely to result from persistence of nucleoli and the possible effects of colchicine and hypotonic treatments that are usually applied. Other phenomena, such as stickiness at metaphase and separation difficulties and fragmentation at anaphase, may result from persistence of nucleoli. Nucleoli were often associated with large chromosomes and sometimes at sites exhibiting faint or clear constrictions. The possibilities of a partial correspondence between sites of persistence and sites of organization, as well as of the organization of nucleolar materials at sites other than the main organizers, are discussed. The persistent nucleoli were not included in daughter nuclei. They either degenerated in the cytoplasm or were eliminated from the cell. The three systems used may represent different intensities of metabolism reflected in the amounts of nucleolar materials built up and the amount that persists.