Increased levels of dihydrofolate reductase mRNA can be measured in normal, growth-stimulated mouse fibroblasts

Levels of mRNA for the enzyme dihydrofolate reductase (EC 1.5.1.3) were determined in growth-stimulated 3T6 cells which contained wild-type dosage of the gene coding for this enzyme. As in the case of methotrexate-resistent cells having highly amplified levels of genes for dihydrofolate reductase, an increase in dihydrofolate reductase mRNA by a factor of 2–4 can be determined when cells enter the S phase. This increase is inhibited by sodium butyrate (which inhibits growth-stimulated 3T6 cells in mid G1 phase) but not by hydroxyurea (which inhibits in early S phase). We conclude that with the available methods it is possible to study the regulation of S phase-specific enzymes after growth stimulation at the level of the mRNA, even if gene amplification is not possible or desirable.     

On the dynamics of asymmetric games

A game dynamical analysis of a simple asymmetric game (two roles with two alternatives each) shows that an interesting class of “semi-stable” heteroclinic cycles leading to a highly unpredictable behaviour can occur in a robust way. Biological examples related to conflicts over ownership and parental investment are analysed.     

Competition and cooperation in catalytic selfreplication

It is shown that in a flow reactor, hypercyclic coupling of self-reproducing macromolecular species leads to cooperation, i.e. none of the concentrations will vanish. On the other hand, autocatalytic selfreproducing macromolecules usually compete, and the number of surving species increases with the total concentration. Both results are proved under very general assumptions concerning the growth rates.This work has been supported by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung, Proj. No. 3502     

Cell clones and pattern formation: Genetic eye mosaics inDrosophila melanogaster

Summary Genetic eye mosaics ofDrosophila melanogaster have been studied by means of anatomical techniques. Using different cell markers it was found that the ommatidia at the boundaries between phenotypes are composed of cells belonging to different clones. Therefore, the formation of an individual ommatidium does not obey a mechanism based on a common clonal origin of its constituent elements. A statistical analysis of mosaic ommatidia shows that there is a significant tendency for the receptor cellsR2-R5 on the one hand and the receptor cellsR1, R6 andR7 on the other to belong to the same cell clone. The implications of these findings are discussed.