Changes in the nuclear structure in the radiation-sensitive CHO mutant cell, xrs-5.

The structural organization of the cell nucleus was investigated by transmission electron microscopy in the radiosensitive Chinese hamster ovary (CHO) cell mutant, xrs-5 (D0 = 45 cGy), relative to parental K1 cells (D0 = 200 cGy). In 99% of all xrs-5 cells, the outer layer of the nuclear envelope was separated from the inner layer, while 96% of K1 cells had closely apposed layers. This separation of the inner and outer layers of the nuclear envelope in xrs-5 cells was not explained by an increased susceptibility of xrs-5 cells to osmotically induced changes because (1) xrs-5 cells retained the altered nuclear periphery even when several different fixation protocols were used and (2) xrs-5 cells were not more susceptible to cell lysis as measured by trypan blue dye exclusion or by the extracellular presence of lactate dehydrogenase.

Morphological and metabolic responses of embryonic hearts to administration of exogenous L-thyroxine.

Injection of 1 microgram L-thyroxine (T4) into the yolk sacs of embryonated chicken eggs at 3 to 6 days of incubation not only induced cardiomegaly but also instigated more rapid differentiation of the heart as an organ and of the individual myocytes per se. Myocytes showed evidence of responding to this dose of exogenous T4 as early as 5 to 6 days of incubation, even though endogenous T4 was not normally forthcoming (in amounts sufficient to provoke organ changes) until 11 to 12 days of incubation. By 7 days of incubation the hearts, conditioned by a single 1 microgram dose of T4, exhibited larger areas occupied by myofibrillar material than controls.

Effects of thyroxine on mitochondrial morphology and uptake of 35S in embryonic chicken livers.

Ultrastructural analyses of reactions of mitochondria in hepatocytes of chicken embryos to low levels of exogenous thyroxine (T4) reveal that such reactions (overall swelling accompanied by disruption of crest geometry) first take place at about 10 days of incubation, T4 having been administered on the 6th day. Physically altered mitochondria may be seen after 11-12 days of incubation but are no longer evident by 13 days. Correlated with the initial evidence of T4 effects on mitochondria at 10 days of incubation is a spurt in hepatocyte proliferation.

Effects of chondroitin-4-sulphate on ultrastructure of ovarian granulosa cells.

Granulosa cells from medium sized porcine ovarian follicles exhibit inhibition of progesterone secretion after both 3 and 6 days of incubation in the presence of 2 mg chondroitin-4-sulphate (C-4-S)/ml. After 3 days of incubation some relatively small and undifferentiated granulosa cells are present in the above cultures. Six days following initiation of incubation in the presence of 2 mg C-4-S/ml many of the larger granulosa cells taken from medium sized follicles reveal lysis and/or resorption of material (probably lipoprotein) from their originally dense staining bodies as well as other indications of stress and degeneration.

Uptake of melanosomes and increased melanin formation by cultured melanoma cells after treatment with isolated melanosomes.

Melanosomes isolated from a subcutaneous Harding-Passey mouse melanoma and purified by density gradient centrifugation were labelled in vitro with 14C-tyrosine or 3H-dihydroxyphenylalanine in the melanin portion. Incubation of monolayer cultures of Harding-Passey melanoma cells during exponential growth phase (wherin cells contained relatively few melanosomes) with isolated and labelled melanosomes during a time-period of up to 3 days resulted in rapid cellular uptake of label (reaching a saturation level after about half a day). Following a lag period of several hours, the melanin content rose near-linearly in the course of 3 days.

On formation of melanosomes in a cultured melanoma line.

Melanosomes are present in abundant numbers in HPM-73 melanoma cells maintained in surum-containing cultures. However, withholding of serum for 3 days caused severe retardation of development of these organelles. Addition of chondroitin-4-sulphate (0.