Cellular Electrophoretic Mobility and the Mitotic Cycle

The electrophoretic mobility of RPMI No. 41 cells grown in suspension, parasynchronized by double thymidine blocking and cold shock, is reported. No. 41 cells have a higher electrophoretic mobility during the mitotic peak phase than at other times in the mitotic cycle. Treatment of parasynchronous cells by neuraminidase reduces the mobility to the same value irrespective of the stage of the cells in the mitotic cycle. The higher electrophoretic mobility of cells in mitotic peak phase is probably due to a higher surface charge density at this time, possibly caused by a higher concentration of ionized neuraminic acid carboxyl groups at the hydrodynamic shear layer. The mobility of nonsynchronous rapidly and slowly growing cells differs; neuraminidase reduces their mobility by proportionately similar amounts. The results suggest that the differences in mobility between rapidly and slowly growing cells cannot be accounted for exclusively by differences in the amount of neuraminic acid groups at the shear layer.     

Characterization of liposomes prepared using a microemulsifier

A new type of device can prepare liposomes continuously, in large quantities and with excellent aqueous space capture efficiency. At initial lipid concentration of 300 μmol/ml these liposomes capture approx. 75% of cytosine arabinoside used as an aqueous space marker. Liposome size can be reduced by increasing the number of times the preparations are recycled through the microemulsifier. Liposomes less than 0.1 μm in diameter, as shown by electron microscopy, can be made easily. Liposomes prepared at 300 μmol/ml, composed of phosphatidylglycerol/phosphatidylcholine/cholesterol in a 0.1:0.4:0.5 molar ratio leaked less than 1% of entrapped cytosine arabinoside (Ara-C) at 4°C, and less than 10% Ara-C at 37°C plus serum, over a 48 h period. These liposomes could be useful for a number of applications including diagnostics, therapeutics and model membrane studies.     

Metabolic and physiologic studies of nonimmune lymphoid cells cytotoxic for fibroblastic cells in vitro

An in vitro reaction between mouse lymphoid cells and target fibroblastic cells in wells of microtest plates, which appears to simulate the in vivo rejection of hemopoietic allografts, has been analyzed for metabolic and physiologic requirements. Protein synthesis was required for only the first few hours of culture. Inhibition of RNA synthesis and alteration of cell surface charge with various agents were without obvious effects. Metabolic slowing at 4 °C or deviation of the pH of the culture medium suppressed the reaction. Thymus cells, which are not cytotoxic in this system, significantly but not completely inhibited the cytotoxicity of lymph node cells. Antiserum directed against target cells specifically protected them from the cytotoxic lymphoid cells in the absence of complement.Precursors of cytotoxic lymphoid cells were radiosensitive, unlike the cytotoxic cells themselves. BALB/c anti-C57BL/6 spleen cell serum and ⁸⁹Sr both are able to prevent rejection of marrow allografts in vitro. Lymphoid cells incubated with this antiserum plus complement lost much of their cytotoxicity but were still effective at high ratios of aggressor to target cells. Lymphoid cells of mice treated with ⁸⁹Sr were effectively cytotoxic but lost practically all of their cytotoxicity afer incubation with the antiserum plus complement. Thus, it appears that this reaction detects two different cytotoxic lymphoid cells, either of which can function in vitro. Both cell types may need to cooperate in vivo during marrow allograft rejections.     

Playing it cool: Characterizing social play,bout termination,and candidate play signals of juvenile and infant Tibetan macaques(Macaca thibetana)

Play behaviors and signals during playful interactions with juvenile conspecifics are important for both the social and cognitive development of young animals.The social organization of a species can also influence juvenile social play. We examined the relationships among play behaviors, candidate play signals, and play bout termination in Tibetan macaques(Macaca thibetana) during juvenile and infant social play to characterize the species play style. As Tibetan macaques are despotic and live in groups with strict linear dominance hierarchies and infrequent reconciliation, we predicted that play would be at risk of misinterpretation by both the individuals engaged in the play bout and by those watching, possibly leading to injury of the players. Animals living in such societies might need to frequently and clearly signal playful intent to play partners and other group members to avoid aggressive outcomes. We gathered video data on 21 individually-identified juvenile and infant macaques(one month to five years of age)from the Valley of the Wild Monkeys, Mt. Huangshan,China. We used all-occurrence sampling to record play behaviors and candidate play signals based on an ethogram. We predicted that play groups would use multiple candidate play signals in a variety of contexts and in association with the number of audience members in proximity to the players and play bout length. In the 283 playful interactions we scored,juvenile and infant macaques used multiple body and facial candidate play signals. Our data showed that juvenile and infant Tibetan macaques use a versatile repertoire of play behaviors and signals to sustain play.     

The effect of polycations on cell membrane stability and transport processes

Summary The interaction of poly-l-lysines of different molecular weights (PL) with Ehrlich ascites tumor cells was studied experimentally with respect to cell surface binding, cell electrophoresis, cytotoxicity and membrane permeability. Although they decrease the net negative charge of Ehrlich ascites cells similarly at low PL concentrations, low molecular weight PL was less cytotoxic and less damaging to the potassium transport mechanism than was high molecular weight PL. At certain PL concentrations, membrane damage was reversible on reincubation in PL-free media. The amount of bound polylysine as determined with fluorescent labeled polylysine was compared by electrophoresis to the amount of polylysine expressed on the electrokinetic surface. The results indicated that only a small fraction of polylysine bound to Ehrlich ascites tumor cells was electrokinetically detectable. The adsorption of polylysine to Ehrlich ascites tumor cells was not describable by the usual adsorption isotherms. It is suggested that the same number of monomeric lysine units of high and low molecular weight PL are adsorbed at the cell electrokinetic surface, but cytotoxicity is dependent on molecular weight. Although the negative charge of human red blood cells could be reversed at low PL concentrations, no such effect could be observed for ELD (a subline of Ehrlich ascites carcinoma) cells even at high PL concentrations. The relationship of PL binding to the stimulation of macromolecular uptake is discussed.     

Ancient origin of high taxonomic richness among insects

Insects are a hyper-diverse group, comprising nearly three-quarters of all named animal species on the Earth, but the environmental drivers of their richness and the roles of ecological interactions and evolutionary innovations remain unclear. Previous studies have argued that family-level insect richness increased continuously over the evolutionary history of the group, but inclusion of extant family records artificially inflated the relative richness of younger time intervals. Here we apply sampling-standardization methods to a species-level database of fossil insect occurrences, removing biases present in previous richness curves. We show that insect family-richness peaked 125 Ma and that Recent values are only 1.5–3 times as high as the Late Palaeozoic. Rarefied species-richness data also tentatively suggest little or no net increase in richness over the past 125 Myr. The Cretaceous peak in family richness was coincident with major radiations within extant groups but occurred prior to extinctions within more basal groups. Those extinctions may in part be linked to mid-Cretaceous floral turnover following the evolution of flowering plants. Negligible net richness change over the past 125 Myr implies that major radiations within extant groups were offset by reduced richness within groups that are now relict or extinct.     

Tuning of the FMN binding and oxido-reduction properties by neighboring side chains in Anabaena flavodoxin

Contribution of three regions (phosphate-binding, 50’s and 90’s loops) of Anabaena apoflavodoxin to FMN binding and reduction potential was studied. Thr12 and Glu16 did not influence FMN redox properties, but Thr12 played a role in FMN binding. Replacement of Trp57 with Glu, Lys or Arg moderately shifted E_ox/sq and E_sq/hq and altered the energetic of the FMN redox states binding profile. Our data indicate that the side chain of position 57 does not modulate E_ox/sq by aromatic stacking or solvent exclusion, but rather by influencing the relative strength of the H-bond between the N(5) of the flavin and the Asn58-Ile59 bond. A correlation was observed between the isoalloxazine increase in solvent accessibility and less negative E_sq/hq. Moreover, E_sq/hq became less negative as positively charged residues were added near to the isoalloxazine. Ile59 and Ile92 were simultaneously mutated to Ala or Glu. These mutations impaired FMN binding, while shifting E_sq/hq to less negative values and E_ox/sq to more negative. These effects are discussed on the bases of the X-ray structures of some of the Fld mutants, suggesting that in Anabaena Fld the structural control of both electron transfer steps is much more subtle than in other Flds.     

A comparative study of body size and clutch size across the parasitoid Hymenoptera

Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the "fast-slow continuum" in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross-species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically-based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.     

Accuracy of prediction equations for determining one repetition maximum bench press in women before and after resistance training

Repetitions to fatigue (RTF) using less than a 1 repetition maximum (1RM) load (RepWt) have been shown to be a good predictor of 1RM strength in men, but such information is scarce in women. The purpose of this study was to evaluate the accuracy of current prediction equations to estimate 1RM bench press performance and to determine whether resistance training changes the capability to predict 1RM from muscular endurance repetitions in young women. Members (n = 103) of a required wellness course were measured for 1RM bench press and RTF using randomly assigned percentages between 60% and 90% of the 1RM (RepWt) before and after 12 weeks of progressive resistance training. The %1RM used to perform RTF remained the same for each individual after training (75.6% +/- 10.3%) as before. One repetition maximum bench press increased significantly after training (28% +/- 21%). Although the change in the group average for RTF (0.6 +/- 6.1) was not significant, the correlation between pretraining and posttraining RTF was moderate (r = 0.66; p < 0.01), and individual differences in percentage change in RTF were substantial (27% +/- 99%). The percentage change in 1RM was not significantly related to initial 1RM (r = -0.05), but it was negatively related to the change in RTF (r = -0.40; p < 0.01). Prediction equations were more accurate in the pretraining and posttraining conditions, in which fewer than 10 RTF were used. Resistance training may alter the relationship between strength and muscle endurance across a wide range of RTF in young women without compromising the accuracy of predicting maximal strength.