Prostaglandin E2 inhibits the activation of cloned T cell hybridomas

To minimize complicating interactions inherent in heterogeneous cell populations, we used a panel of cloned murine autoreactive (E8.A1) and antigen-specific (HEL.C10, HEL.B14) T cell hybridomas to examine the effect of prostaglandin E2 (PGE2) on T cell activation. These T cells secrete interleukin 2 (IL 2) when co-cultured with a cloned population of I region-matched stimulator cells (TA3), or with mitogenic signals in the absence of TA3 stimulator cells. Physiologic concentrations of PGE2 inhibited the induction of IL 2 secretion by the T cell hybridomas tested, when they were activated either by TA3 cells or by mitogenic signals. IL 2 production was inhibited in a dose-dependent manner by concentrations of PGE2 between 10(-7) and 10(-11) M, with 50% inhibition occurring at 10(-10) M. Pretreatment of the T hybridoma cells with 10(-7) M PGE2 for 1 hr before culture also resulted in marked inhibition of IL 2 secretion. Similar pretreatment of the TA3 cells did not affect their ability to activate the T cell hybridomas. PGE2 at 10(-8) M induced a 30-fold increase in cAMP levels within 25 min of addition to culture of the E8.A1 T cell hybridoma, but caused no significant elevation of cAMP levels in TA3 cells. The direct addition of dibutyryl cAMP (dcAMP) to cultures of E8.A1 cells resulted in marked inhibition of IL 2 secretion when stimulated by TA3 or by mitogenic signals, with an average of 80% inhibition occurring at 10(-4) M dcAMP. PGE2 and dcAMP also inhibited the growth of E8.A1 cells. Initially, cell growth was virtually halted, but began to recover between 24 and 48 hr after the addition of either PGE2 or dcAMP. Neither PGE2 nor dcAMP inhibited the division of TA3 cells. High affinity binding sites for PGE2 were detected in the E8.A1 T cell hybridomas with an apparent Kd of 7.6 X 10(-10) M, which is consistent with the functional data. No specific binding was detected in the TA3 stimulator cells. These findings suggest that the immunosuppressive effects of PGE2 are localized to the T cell, are receptor regulated, and may be mediated by the associated increase of cAMP levels in the T cell hybridomas.     

Evidence Inconsistent with the Blaauw Model of Phototropism

The Blaauw model of phototropism equates the inhibition of growthat the illuminated side of a unilaterally illuminated organwith the blue light inhibition of overall organ extension evidentwhen some shoots are exposed to uniform blue light However,a study of the growth responses of Avena coleoptiles exposedto omnilateral, equal bilateral, unequal bilateral and unilateralblue light has revealed some light induced growth rate changeswhich cannot be explained by the Blaauw model. The growth responsesof cells at the illuminated and shaded sides of phototropicallystimulated coleoptiles seem to depend on the existence of alight gradient across the whole organ rather than the absolutelevels of light at either side. Key words: Phototropism, Avena coleoptile, Blaauw hypothesis, Blue light, Growth inhibition     

Escherichia coli CAN lacks a tRNA-processing nuclease.

Escherichia coli strain CAN is unable to support the growth of bacteriophage T4 strains requiring the suppressor function of T4 tRNASer. Biochemical analysis of the mutant strain revealed that it is deficient in a RNase which acts on the artificial tRNA precursor tRNA-C-U.     

Kinetics of beta-glucuronidase induction by androgen. Genetic variation in the first order rate constant

Measurements of enzyme activity, rates of protein synthesis, and mRNA activity suggest that the induction of beta-glucuronidase in mouse kidney in response to androgen is regulated at a pretranslational level. Following an initial lag period, the rate and extent of induction follow the rules of simple turnover kinetics and can be described in terms of a zero order rate constant for acquisition of mRNA activity (ka) and a first order rate constant for loss of activity (kb). Genetic variation in kb, described here for the first time, alters the half-time and extent of induction. Variation in kb is independent of previously described variation in ka and, unlike changes in ka, is not associated with change in the lag time. The DNA sequences determining kb, like those determining ka, are genetically linked to the structural gene for beta-glucuronidase. Following the removal of androgen, beta-glucuronidase activity, rate of synthesis, and mRNA activity all decline rapidly with half-lives of 1-2 days. Even in the most rapidly inducing strains, this is significantly faster than the half-time for induction determined by kb. Furthermore, genetic variation in kb does not affect the rate of de-induction. These facts suggest that kb may not describe the turnover of beta-glucuronidase mRNA, but rather the turnover of another step in the induction process.     

The Enucleation of Cells on Plastic Leighton Coverslips

A simple enucleation technique that facilitates autoradiographic and electron microscopic examination of cytoplasms is described. Cells were grown on commercially available plastic Leighton coverslips and these were centrifuged in the presence of cytochalasin B. The centrifugation requires no special holders and only a high speed centrifuge. Enucleation frequencies of greater than 90% were obtained for Chinese hamster fibroblasts and mouse B-82 cells.     

The Effect of Decreasing the External Salinity on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

The euryhaline unicellular green alga Dunaliella tertiolectalost intracellular glycerol when subjected to a decrease inexternal salinity. After the salinity was decreased, photosynthesiswas inhibited for at least the first 100 min, but dark oxygenuptake was transiently stimulated. The extent of the 519 nmfield-indicating absorption change induced by photosystem Ialone was inhibited by decreasing the salinity, but other photosyntheticparameters were largely unaffected. A comparison of these resultswith hypertonic stress indicated that although both stressesinhibit the overall process of photosynthesis, they do so bydifferent mechanisms. Resuspending the algal cells in distilledwater resulted in an inhibition of all the photosynthetic parametersmeasured. Key words: Dunaliella, Photosynthesis, Hypotonicity     

Teixeiria lusitanica, a new fossil flower from the Early Cretaceous of Portugal with affinities to Ranunculales

A charcoalified fossil flower bud of a new genus and species (Teixeiria lusitanica) is described from the Early Cretaceous of Portugal. The flower is actinomorphic and unisexually male. At the base of the bud there are several bracts of different sizes, which are followed by sepal-like and petal-like tepals. Bracts and perianth organs seem to be arranged spirally and to exhibit transitions between different organ categories. The androecium has numerous stamens in two sizes, but with unclear arrangement. Pollen is small and tricolpate with a perforate tectum and a densely columellate infratectal layer. No carpels or remains of carpels could be observed on the floral axis. Teixeiria lusitanica shows most affinities to members of Ranunculales. There are also some similarities with Berberidopsis (Berberidopsidaceae, Berberidopsidales) and members of the Saxifragales (Hamamelidaceae and Daphniphyllaceae).     

Coordinate regulation of histone mRNAs during growth and differentiation of rat myoblasts

To determine whether histone genes are coordinately regulated, histone mRNA concentrations were measured in exponentially growing L6 myoblasts, S-phase synchronized myoblasts and in differentiating myoblasts. The levels of various histone mRNA subspecies declined rapidly and coordinately once myoblasts were given the signal to differentiate. mRNA levels were reduced on average to 1-5% of the amount observed in exponentially growing cells by 48 h after the signal to differentiate. The reductions occurred in concert with the cessation of DNA synthesis as the cells differentiated. Inhibition of DNA synthesis by treating myoblasts with Ara-C or hydroxyurea resulted in a histone mRNA half-life of 10-13 min for each of the histones examined. One example of non-coordinate regulation was observed however among the H4 mRNA subspecies in S-phase synchronized cells. The levels of two major subspecies of H4 mRNA increased coordinately in S-phase compared to levels observed in cells growing exponentially. A third subspecies of H4 mRNA on the other hand was found to decline by 50%. These studies suggest that the majority of histone mRNA subspecies are under coordinate control, although one exception has been noted among the subspecies of histone H4.