DNA repair kinetics in irradiated undifferentiated and terminally differentiated cells

The brains of male Fisher 344 rats bearing 80-150 mg intracerebral 9L/Ro tumors were irradiated with doses of 1,250-5,000 rads of x- or gamma-rays. At various times after irradiation, the cerebellum and tumor were excised, dissociated into single cells and the DNA from these cells sedimented through alkaline sucrose gradients in zonal rotors with slow gradient reorienting capability. Quantitation of the DNA repair kinetics demonstrated that the process in both tumor cells and neurons has a fast and slow phase. Although all other alternatives cannot be completely eliminated, we suggest that these two phases are most reasonably interpreted as representing repair of lesions in very accessible and less accessible regions of the genome rather than 1) repair of different types of lesions such as single- or double-strand breaks or 2) removal of immediate breaks and breaks induced during excision repair of latent base damage. The slow repair phase is saturable, but not inducible in both tumor cells and neurons. The data suggest that tumor cells restore their chromosomal DNA structure to the unirradiated state faster than neurons because 1) they contain more of the repair system per unit of DNA and 2) a larger proportion of their genetic material is comprised of very accessible regions. The data also suggest that the entire tumor cell genome may be accessible to the repair enzyme(s), while it is possible that a portion of the neuronal genome may be completely inaccessible.     

CELL CYCLE COMPARTMENT ANALYSIS OF CHINESE HAMSTER CELLS IN STATIONARY PHASE CULTURES

The distribution of Chinese hamster cells with respect to the compartments of the cell generation cycle was studied in cultures in the stationary phase of growth in two different media. A measure of the state of depletion of the nutrient medium was formulated by defining a quantity termed the nutritive capacity of the medium. This quantity was used to verify that the cessation of cell proliferation is due to nutrient deficiencies and not to density dependent growth inhibition. Cell cultures in stationary phase were diluted into fresh medium and as growth resumed, mitotic index, cumulative mitotic index, label index and viability were measured as a function of time. The distribution of cells with respect to compartments of the cell generation cycle in stationary phase populations was reconstructed from these data. Stationary phase populations of Chinese hamster cells that retained the capacity for renewed growth when diluted into fresh medium were found to be arrested in the G₁ and G₂ portions of the cycle; the relative proportion of these cells in G₁ increased with time in the stationary phase, but the sequence differs in the two media. In early stationary phase, in the less rich medium, more cells are in G₂ than in G₁. Also in this medium a fraction of the population was observed to be synthesizing DNA during stationary phase, but this fraction was not stimulated to renewed growth by dilution into fresh medium.     

Changes in isozyme patterns between monokaryons and dikaryons of a bipolar Coprinus

Proteins and isozymes of several different classes of enzymes in partially purified protein extracts of monokaryons, dikaryons, and monokaryon mixtures of a bipolar Coprinus sp. were separated on polyacrylamide gels by slab electrophoresis. Differences in protein and isozyme spectra were correlated with the operation of the incompatibility factors and with the results of Wang and Raper on Schizophyllum. It was concluded that the shift from monokaryon to dikaryon mediated a major change in the nature, quantity, or distribution of the proteins of this Coprinus sp.     

The sea anemone Calliactis tricolor and its association with the Hermit crab Dardanus venosus

The association of certain sea anemones and hermit crabs is established in different ways according to the species involved. The present study shows that the behaviour patterns of the two partners in associations between Calliactis tricolor (Lesueur) and Dardanus venosus (H. M. Edwards) in the Caribbean are similar to those seen in the Mediterranean C. parasitica and D. arrosor .
Although about half the crabs display an active behaviour pattern in laboratory trials, the anemone frequently settles on shells unaided and most C. tricolor respond to molluscan shells by clinging with their tentacles until the pedal disc can be attached. As a rule it is necessary for the anemone to relax and to cling to the shell if the crab is to be successful in transferring the anemone to its shell.
The behaviour patterns of D. venosus include a distinctive tapping of the edge of the base of C. tricolor after which the anemone is pulled or lifted off and transferred to the shell. An experimenter can also cause the anemone to relax and to detach itself by tapping the edge of the base with plastic rods after the manner of the crab.
The mechanisms by which the tentacles of Calliactis cling to, and by which the base settles upon, shells still remain to be elucidated. The participation of nematocysts in these processes could not be demonstrated in this study.
C. tricolor is found on some other pagurid and non-pagurid crabs in various localities. These associations need to be investigated fully in order that the behaviour patterns of C. tricolor may be correctly interpreted and compared with those of other species of Calliactis .     

The 131I Ortho-iodohippurate Photoscan in Human Renal Allografts

Nine examples, in seven patients, from a large cadaver renal allograft program, illustrate the value of radio-hippuran photoscans in differentiating causes of post-implant oliguria. Hippuran scans are shown to be more valuable than chlormerodrin scans when renal function is acutely depressed. Hippuran scans aided in the decision to remove kidneys in four cases of severe oliguria and to retain kidneys in two others. In two further examples, extravasation of urine was detected by scanning after radio-hippuran injection when other tests had failed to do so.The technique of radio-hippuran scanning has a place in the differentiation of acute and subacute renal dysfunction and has proved particularly valuable in the early oliguric complications of a cadaver renal transplant program.