Modulation of DNA precursor pools, DNA synthesis, and ultraviolet sensitivity of a repair-dificient CHO cell line by deoxycytidine

The presence of 2 mM deoxycytidine (CdR) in growth medium substantially increased the deoxycytidine triphosphate (dCTP) and deoxuthymidine triphosphate (dTTP) pools in a Chinese hamster ovary cell line, CHO-K1, and in a radiation-sensitive mutant, xrs-5, derived from it (Jeggo et al., 1982). We observed significant differences in alkaline-sucrose gradient profiles of pulse-labeled DNA from unirradiated CHO-K1 and xrs-5 cells. For the latter cell line, a sizable fraction of the DNA synthesized during 5 or 10 min of growth subsequent to a 5-min radiolabeling period was found to co-sediment with large-chromosome DNA. This characteristics of xrs-5 was dramatically reduced by the presence of 2 mM CdR in the culture medium, and the UV resistance of the mutant increased to nearly that of the parent cell line under these culture conditions. These results show that the locus conferring UV-radiation sensitivity to xrs-5 affects DNA replication and that replicative activity and UV-radiation sensivity are jointly modulated by CdR, possibly through its impact on the size of deoxynucleoside triphosphate pools.     

Clinical adaptation of a high-performance liquid chromatographic method for the assay of pyridoxal 5′-phosphate in human plasma

Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation.     

Validation of an in vivo method for monitoring ovarian development in the grey mullet (Mugil cephalus L.)

The validity of using extruded intra-ovarian oocytes for in vivo assessment of ovarian maturity in the grey mullet was established. The diameter of sampled, unfixed oocytes was used as a reference point for comparative purposes. Analysis of variations in oocyte diameters among samples removed from seven different ovarian locations indicated that mullet oocytes develop in synchrony and that in vivo samples taken from any area in the ovary would be representative of the entire ovary. Statistical analyses of oocyte diameters and diameter-frequency distributions data from duplicate in vivo samples removed from the same ovarian site in each of 17 females showed no significant differences and validated the accuracy of the method. Similar comparisons of data from in vivo and in vitro samples revealed no statistically significant differences.     

Effects of trichomes on the behavior and distribution of Platyprepia virginalis caterpillars

Trichomes are an important physical resistance mechanism of plants, as they reduce insect herbivore movement, feeding, and digestion. However, we know little about how trichomes influence herbivore distributions and populations. We conducted laboratory and field experiments to evaluate the preferences of Platyprepia virginalis (Boisduval) (Lepidoptera: Arctiidae) caterpillars to natural and manipulated densities of trichomes on their primary food, Lupinus arboreus Sims (Fabaceae). We then conducted field surveys to determine whether variation in trichome density among lupine bushes affected caterpillar spatial distribution on the landscape. Platyprepia virginalis caterpillars preferred lupine leaves with fewer trichomes in choice and no‐choice experiments. In the field, caterpillar feeding damage was found more often on leaves with fewer trichomes. These preferences scaled up to the level of bushes in the landscape such that more caterpillars were found on bushes with lower trichome densities than on bushes with higher trichome densities. This is one of few studies to show the potential for trichome density to influence herbivore population size and distribution in a natural system at a landscape level. The results are consistent with trichomes functioning as a resistance mechanism with consequences for herbivore choice, performance, and distribution.     

Effect of dibutyryl cAMP on cell cycle progression of rat brain tumor cells in vitro

Summary Autoradiographic and flow microfluorometry analyses have been applied to a study of perturbed cell kinetics in 9L rat brain tumor cells treated with dibutyryl cyclic AMP and theophylline alone and in combination in vitro. At a concentration of 1 mM each, cell growth ceased shortly after the administration of these drugs. The results indicate that cells in S and G₂ phase at the time of drug administration can undergo mitosis even though a considerable prolongation of G₂ phase was apparent. However, cells in G₁ at the time of drug administration were arrested in that phase whereas those cells in S or G₂ were able to complete one mitosis before becoming arrested in the G₁ phase. This blocking effect was reversible, and cells resumed proliferation at a normal rate shortly after the removal of these drugs. This work was supported in part by NIH Cancer Research Center Grant CA-13525 and CA-19992 from NCI, and by the Association for Brain Tumor Research. Presented at the 6th International Cell Cycle Conference, March, 1976, New Orleans, Louisiana. The tumor used in this study was provided by William H. Sweet, Paul T. Kornblith, Janette L. Messer and Beverly O. Whitman of the Massachusetts General Hospital, Boston, Massachusetts.     

Solution-Phase, parallel synthesis and pharmacological evaluation of acylguanidine derivatives as potential sodium channel blockers

Solution-phase synthesis of various acylguanidine derivatives and the evaluation of a small library of compounds as potential sodium channel blockers are described.     

Hydraulic acclimation in a Mediterranean oak subjected to permanent throughfall exclusion results in increased stem hydraulic capacitance

Stem water storage capacity and hydraulic capacitance (C_S) play a crucial role in tree survival under drought-stress. To investigate whether C_S adjusts to increasing water deficit, variation in stem water content (StWC) was monitored in vivo for 2 years and related to periodical measurements of tree water potential in Mediterranean Quercus ilex trees subjected either to permanent throughfall exclusion (TE) or to control conditions. Seasonal reductions in StWC were larger in TE trees relative to control ones, resulting in greater seasonal C_S (154 and 80 kg m⁻³ MPa⁻¹, respectively), but only during the first phase of the desorption curve, when predawn water potential was above −1.1 MPa. Below this point, C_S decreased substantially and did not differ between treatments (<20 kg m⁻³ MPa⁻¹). The allometric relationship between tree diameter and sapwood area, measured via electrical resistivity tomography, was not affected by TE. Our results suggest that (a) C_S response to water deficit in the drought-tolerant Q. ilex might be more important to optimize carbon gain during well-hydrated periods than to prevent drought-induced embolism formation during severe drought stress, and (b) enhanced C_S during early summer does not result from proportional increases in sapwood volume, but mostly from increased elastic water.     

Causing Physical Change to Create Art

The presentation involves students in a hands-on analysis of artifacts to create a time line of their local area's past societies. This exercise is more of a unit rather than a one-time activity. Procedures, ideas, and background for developing your own unit are presented in this article. The purpose of this unit is to engage students in applying the scientific method to archaeological research. Students will gain experience in designing and conducting their own investigations.