Cell cycle population effects in perturbation studies

Growth condition perturbation or gene function disruption are commonly used strategies to study cellular systems. Although it is widely appreciated that such experiments may involve indirect effects, these frequently remain uncharacterized. Here, analysis of functionally unrelated Saccharyomyces cerevisiae deletion strains reveals a common gene expression signature. One property shared by these strains is slower growth, with increased presence of the signature in more slowly growing strains. The slow growth signature is highly similar to the environmental stress response (ESR), an expression response common to diverse environmental perturbations. Both environmental and genetic perturbations result in growth rate changes. These are accompanied by a change in the distribution of cells over different cell cycle phases. Rather than representing a direct expression response in single cells, both the slow growth signature and ESR mainly reflect a redistribution of cells over different cell cycle phases, primarily characterized by an increase in the G1 population. The findings have implications for any study of perturbation that is accompanied by growth rate changes. Strategies to counter these effects are presented and discussed.     

Reaction of endotoxin and surfactants. I. Physical and biological properties of endotoxin treated with sodium deoxycholate

Ribi, E. (Rocky Mountain Laboratory, Hamilton, Mont.), R. L. Anacker, R. Brown, W. T. Haskins, B. Malmgren, K. C. Milner, and J. A. Rudbach. Reaction of endotoxin and surfactants. I. Physical and biological properties of endotoxin treated with sodium desoxycholate. J. Bacteriol. 92:1493-1509. 1966.-Endotoxins from three species of gram-negative bacteria were shown to be dissociated by the bile salt sodium deoxycholate (NaD) into nontoxic subunits with molecular weights of about 20,000. When the bile salt was removed by dialysis, the subunits reaggregated in an orderly manner to form a relatively uniform population of biologically active endotoxin particles with average molecular weights of 500,000 to 1,000,000. If a small amount of human plasma was added to the dissociated endotoxin before removal of the NaD, reassociation apparently did not occur and the preparation remained nonpyrogenic. However, the plasma protein could subsequently be removed from the endotoxin subunits, and reaggregation to the toxic form would then occur. The studies on the physical nature of endotoxin performed with biophysical solution techniques were supplemented and confirmed by direct examination of the endotoxin polymers by electron microscopy. The results of these studies were consonant with the theory that the biologically active endotoxic elements are composed of micellar aggregates of linear lipopolysaccharide subunits.     

High resolution ultrasound-guided microinjection for interventional studies of early embryonic and placental development in vivo in mice

Background  

In utero microinjection has proven valuable for exploring the developmental consequences of altering gene expression, and for studying cell lineage or migration during the latter half of embryonic mouse development (from embryonic day 9.5 of gestation (E9.5)). In the current study, we use ultrasound guidance to accurately target microinjections in the conceptus at E6.5–E7.5, which is prior to cardiovascular or placental dependence. This method may be useful for determining the developmental effects of targeted genetic or cellular interventions at critical stages of placentation, gastrulation, axis formation, and neural tube closure.     

Effect of inhibitors of sterol biosynthesis on growth and sexuality of pythium and zygorhynchus

Seven commercial inhibitors of sterol biosynthesis were tested for their effect upon vegetative growth and sexuality in Pythium acanthicum and Zygorhynchus moelleri. Five compounds (SKF 525, Chlorpropamide, Tolbutamide, Benzmalacene, AY 9944) inhibited both growth and sexuality of both fungi and two (SKF 7732 and SKF 7997) were ineffective. Pythium was more sensitive to the activity of the inhibitors than was Zygorhynchus. None of the compounds tested inhibited sexuality without similarly reducing vegetative growth.NRCC No. 15402