Distribution of interdivisional times in proliferating and differentiating Friend murine erythroleukaemia cells

The interdivisional times of Friend murine erythroleukaemia cells which are growing continuously, or during terminal erythroid differentiation after exposure to dimethyl sulphoxide (DMSO), were determined by time lapse video photography. The median interdivisional times were found to increase from 11.75 hr before exposure to DMSO, to 24.0 hr at 72 hr after exposure. This increase in median interdivisional time was accompanied by an increase in heterogeneity of interdivisional times (%CV = 8.5----40.8), by an increase in the similarity of sister interdivisional times (ryy = 0.622----0.925), and by a decrease in the fraction of cells observed to divide (F = 1.0----0.807). Cells exposed to DMSO for 72 hr can be induced to divide at least once with nearly normal interdivisional times, if they are resuspended at a tenfold higher cell concentration. Computer simulations of cell cycle regulation, based on the opposing reactions model of Murphy, generate interdivisional time distributions which resemble the experimental data better than the single transition probability model of Smith and Martin.     

Embryonic stem cell lines derived from blastocysts by a simplified technique

We have isolated euploid, pluripotent stem cell lines directly from mouse blastocysts by a simple culture technique. Our method permits cell lines to be derived from individual embryos, without the use of ovariectomy, immunosurgery and conditioned medium. We cultured individual intact blastocysts in MicroTest plates on top of a feeder layer of lethally irradiated STO mouse fibroblasts in a 10-microliters volume of Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal calf serum (FCS). The cell lines maintain a stable complement of 40 chromosomes, form embryoid bodies and differentiate both in culture and in solid tumors.     

Multiple dioxygenation by lipoxygenase of lipids containing all-cis-1, 4, 7-octatriene moieties.

Soybean lipoxygenase-1 acting upon polyunsaturated fatty acids containing a suitably positioned all-cis-1,4,7-octatriene moiety generates bishydroperoxy derivatives while consuming approximately 2 mol of O₂ per mole of substrate. The reaction has been separated into two steps: The first is marked by the rapid monohydroperoxidation of the starting material and the second is marked by the much slower hydroperoxidation of the first product. All of the compounds which are successfully converted to bishydroperoxy derivatives contain an ω6,9,12 grouping of cis double bonds. α-Linolenic acid (ω3,6,9) cannot serve as a substrate because its preferred site of oxygenation is in the center of the octatriene moiety. The K_m for arachidonic acid in the reaction leading to the singly hydroperoxidized monohydroperoxide is 8.6× 10^?5, m, which is approximately 200 times smaller than the K_m for the monohydroperoxide in the second step leading to the bishydroperoxide. All of the substrates which undergo double dioxygenation form conjugated trienes.     

Distribution of Interdivisional Times In Proliferating and Differentiating Friend Murine Erythroleukaemia Cells

Abstract. The interdivisional times of Friend murine erythroleukaemia cells which are growing continuously, or during terminal erythroid differentiation after exposure to dimethyl sulphoxide (DMSO), were determined by time lapse video photography. the median interdivisional times were found to increase from 11.75 hr before exposure to DMSO, to 24.0 hr at 72 hr after exposure. This increase in median interdivisional time was accompanied by an increase in heterogeneity of interdivisional times (% CV = 8-5 → 40.8), by an increase in the similarity of sister interdivisional times (r_yy= 0.622 → 0.925), and by a decrease in the fraction of cells observed to divide ( F = 1. 0 → 0.807). Cells exposed to DMSO for 72 hr can be induced to divide at least once with nearly normal interdivisional times, if they are resuspended at a tenfold higher cell concentration. Computer simulations of cell cycle regulation, based on the opposing reactions model of Murphy, generate interdivisional time distributions which resemble the experimental data better than the single transition probability model of Smith and Martin.     

Immunochemical Characterization of Plaque Mutants of Simian Virus 40

Analysis of large and small plaque mutants of simian virus 40 using antisera prepared against each has revealed quantitative and possibly qualitative antigenic differences for each plaque type. A sensitive micro radioisotope precipitation test permitted evaluation of immunochemical similarities and differences of capsid antigens by inhibition of precipitation.     

Altered trophoblast functions in implantation-defective mouse embryos

Extracellular proteases, such as plasminogen activator (PA), may play a role in the invasive action of trophoblasts during blastocyst implantation in mice. Detailed analysis of proteases released by trophoblasts must be carried out in culture for practical reasons, but the in vitro results should ideally be related to implantation in utero to test the validity of the conclusions in the model system. The implantation-defective mutant (tw73) allows us to investigate alterations of trophoblasts in culture which will reflect their altered functions in utero. The trophoblasts of mutant embryos attached and proliferated in culture to the same extent as control embryos. Therefore, the mutant effect is not to kill or stop the division of these cells. However, trophoblasts of tw73 homozygotes showed decreased invasive ability when transplanted into testes. To examine the biochemical basis of altered invasive behavior in mutants, PA activity released by blastocysts in culture was measured. Medium conditioned by tw73 homozygotes contained less PA fibrinolytic activity than culture medium of control embryos. The correlation between decreased in vitro PA activity and the invasive defects seen in utero and ectopically, supports the involvement of PA in the invasive phase of the implantation process.