Asparagine-requiring tumor cell lines and their non-requiring variants: cytogenetics, biochemistry and population dynamics

Asparagine-requiring Jensen and Walker rat tumor cells and their asparagine-independent variants have been analyzed. The following results were obtained: (1) Both cell lines have very low levels of asparagine synthetase, and non-requiring revertants isolated from these lines have elevated levels of the enzyme. (2) No differences in chromosome number were detected between the parent Jensen line and five Jensen non-requiring revertants isolated from it. (3) Both Jensen and Walker cells undergo asparagineless death when deprived of this amino acid, although the Jensen cells do so at a more rapid rate. (4) Jensen requiring lines are at a selective advantage when grown in competition with non-requiring variants in complete medium, and their growth rate is more rapid when grown separately. The selective coefficients for the variant with respect to the asparagine-requiring parent ASN(-) line were 0.94 for the competition experiments and 0.83 for growth rate estimates. (5) A somatic cell hybrid between Chinese hamster cells (which require asparagine at low densities, and posses measurable synthetase activity) and the Walker line was found to be asparagine-independent, and it possessed enzyme levels equivalent to the hamster parent. The results of these investigations suggest a parallel with microbial auxotrophic mutants and can be understood in terms of alterations within nuclear structural genes.

Population dynamics of purine and pyrimidine analog sensitive and resistant mammalian cells grown in culture

The population dynamics of purine analog resistance have been studied. Two types of reconstruction experiments were performed: cloning numbers of azaguanine resistant, BUdR resistant, and sensitive cells were plated in the presence of a large number of the opposite genotype, which were made to act as a feeder layer by inactivating them with either the appropriate analog or the reverse selective HAT medium. These experiments demonstrate that there is no significant metabolic cooperation between drug resistant and drug sensitive cells, with the exception of BUdR sensitive cells, which at high densities inhibit the cloning ability of BUdR resistant cells in the presence of the drug. Thus the purine analog resistance system can be used for obtaining quantitative data concerning such parameters as mutation and selection, while at high cell densities the pyrimidine analog system appears to be unsatisfactory.——A second series of experiments indicates that, in artificial mixtures of sensitive and resistant cells grown in standard medium, the resistant cells are at a selective disadvantage and will be reduced eventually to the frequency which is observed in wild type populations.

Seminal vesicle formation and specific male protein secretion by female cells in allophenic mice

The relation of cellular sex genotype to phenotype was examined in seminal vesicles of adult allophenic mice with cellular sex chromosome mosaicism. Each animal originated from conjoined blastomeres of an embryo of female (XX) and one of male (XY) constitution, from different inbred strains. Cells of both sexes were detected in bone marrow and certain other somatic tissues; cellular sex of seminal vesicles was deduced from strain-associated electrophoretic variants of proteins coded for at autosomal loci. Seminal vesicles composed partly or entirely of female cells were found in male and pseudohermaphrodite individuals. In a pseudohermaphrodite, both allelic variants of the tissue-specific normal male seminal vesicle protein (Svp-locus) were present, signifying that female as well as male cells were synthesizing the protein. Male-determining factors on the Y chromosome are thus not required in cells that differentiate into functional seminal vesicles.