ANALYSIS OF MICROTUBULE STRUCTURE IN EUGLENA GRANULATA

The microtubules associated with the pellicle, reservoir and locomotory flagellum of Euglena granulata were subjected to rotational analysis using the technique of Markham et al. The results indicate that the microtubules have 11-14 subunits when viewed in transverse section. Rotational analysis of the entire locomotory flagellum was also conducted to better demonstrate the nature of the arms extending from the peripheral microtubules.     

Chronic exposure to inhaled anesthetics increases cholesterol content in Acholeplasma laidlawii

Acholeplasma laidlawii cells were grown in cholesterol-enriched medium and exposed continuously to either air (control), 4.0 vol.% halothane in air at 1 atm pressure (4% atm halothane), or 80% cyclopropane in oxygen for 24 h at 37°C. Cells grown in the presence of 4% atm halothane or 80% cyclopropane had approximately twice as much membrane cholesterol content/mg protein as the control cells. Cells grown in an anesthetic environment also tended to have a higher membrane cholesterol/phospholipid molar ratio compared to control cells. Membranes isolated from halothane-exposed cells grown in a cholesterol-enriched medium were more ordered at 37°C (measurements were made with no anesthetic present) than membranes from control cells grown in an identically enriched medium. This difference in membrane physical state between control and anesthetic-exposed cells decreased as the temperature decreased, and disappeared at approx. 23°C. Continuous exposure of A. laidlawii to 4% atm halothane or 80% cyclopropane for 24 h did not markedly affect membrane fatty acid composition, either in cells grown on an unsupplemented medium or in cells grown in a medium enriched in myristic, palmitic or stearic acids. These results further support the hypothesis that an increased membrane cholesterol content may play a role in the tolerance or dependence that develops after chronic exposure to anesthetic agents.     

Human lymphocyte tubulin: Purification and characterization in normal and leukemic cells

Tubulin has been purified from human blood and tonsil lymphocytes. Using gel filtration, the molecular weight of human lymphocyte tubulin was estimated to be 119 000. The proteins was shown to consist of two subunits, with molecular weights of 61 000 and 58 000 comparable to the α and β polypeptides of human brain tubulin. A partial identity reaction was observed between lymphocyte tubulin and human tubulin when tested by double immunodiffusion against a rabbit anti-human brain tubulin antibody. In the presence of GTP, the purified protein polymerized to form microtubules. Tubulin was localized to the cell's juxtacentriolar region by immunofluorescence and electron microscopy. When assayed by a colchicine-binding assay corrected for time decay, the binding affinity was 1.50 ± 0.86 · 10⁶M^?1 and a level in normal lymphocytes of 1.21 · 10^?2 ± 0.79 g/g of soluble protein was determined. Since chronic lymphocytic leukemia lymphocytes have an anomalous capping behavior as well as an unusual susceptibility to colchicine toxicity, the properties and levels of tubulin were determined in these cells. Similar values were obtained for the level, decay rate, molecular weight, and K_a for colchicine as for normal lymphocytes. Chronic lymphocytic leukemia lymphocyte tubulin polymerized in a normal fashion. It thus appears that a decrease in the quantity or function of tubulin does not account for these anomalies in the chronic lymphocytic leukemia lymphocyte.     

Introgressive hybridization of tilapias in Zimbabwe

Three species of tilapia native to Zimbabwe, Oreochromis mossambicus, O. mortimeri and O. macrochir are not naturally sympatric, but because of transplantation they have been brought into sympatry. Allozymes of fish examined from Lakes Kariba, Kyle and Chivero showed evidence of introgressive hybridization. The data showed non-random mating populations in Lakes Kariba and Kyle. All three reservoirs displayed individuals with intermediate principal component scores and hybrid index scores indicating hybridization.     

Developmental plasticity in the queen-polymorphic ant Temnothorax longispinosus

Females of social Hymenoptera show developmental plasticity in response to varying social and environmental conditions, though some species have strong genetic influences on the form of the female reproductives. In ants, a queen polymorphism can occur in which large queens initiate new colonies on their own, while small queens enter established nests. Most queen polymorphisms studied to date originate due to genetic differences between individuals of differing form. Here, we report on the development of female form in response to social factors within the nest in the queen-polymorphic ant Temnothorax longispinosus. Three queen size morphs occur: a rare large queen with higher fat stores that can found new colonies independently, a large queen that has low fat stores and is behaviorally flexible, and a small queen that rejoins the natal nest. Both in nesting units collected from the field and those reared in the lab, queen presence during larval development led to fewer larvae developing as gynes (virgin, winged queens), and most of those gynes were the small morph. This queen effect is transferred to developing gyne larvae by close, physical interaction between queens and workers, and causes slower larval development. We conclude that gyne size, and therefore reproductive behavior, in T. longispinosus is developmentally plastic in response to queen presence. Plasticity in reproductive behavior may be an adaptive response to the nest sites utilized by this species. T. longispinosus nests predominantly in acorns and hickory nuts, which can vary dramatically from 1 year to the next. Since queens are more likely to be present in each nesting unit when fewer nest sites are available, the queen effect that results in more small gynes produced links the expression of colony-founding traits to ecological conditions across habitat patches.