Genetics of somatic cell surface antigens. III. Further analysis of the AL marker.

The AL antigen present on the surface of various human somatic cells, and on those hybrids of human and Chinese hamster ovary cells which have retained human chromosome number 11, has been resolved into at least two separate antigenic activities, a1 and a2. Specific antisera active against each antigen separately have been prepared. By treatment of the original AL+ hybrid with mutagenic agents and selection in particular antisera, stable clones are preparable whose phenotypic behavior corresponds to the antigenic compositions a1+ a2-, a1- a2+, and a1- a2-. The adsorption behavior of these variants for specific antisera is consistent with their phenotypic assignments.     

Phenylalanine hydroxylase activity in mammalian cells

Survey of twelve mouse tissues revealed the presence of appreciable phenylalanine hydroxylase activity in the pancreas and kidney as well as the liver but in no other of the tissues tested. Single cell suspensions of mouse liver were prepared by use of tetraphenylboron. The enzyme activity of such suspensions was much more stable than that of liver extracts, and permitted determination of the Michaelis-Menten constant, the pseudo-first order reaction velocity constant on a cell-number basis, and the temperature coefficient and apparent activation energy of the enzyme activity. Possible applications of these methods to problems in cellular biology have been indicated.     

A guide to choosing and implementing reference models for social network analysis

Analysing social networks is challenging. Key features of relational data require the use of non-standard statistical methods such as developing system-specific null, or reference, models that randomize one or more components of the observed data. Here we review a variety of randomization procedures that generate reference models for social network analysis. Reference models provide an expectation for hypothesis testing when analysing network data. We outline the key stages in producing an effective reference model and detail four approaches for generating reference distributions: permutation, resampling, sampling from a distribution, and generative models. We highlight when each type of approach would be appropriate and note potential pitfalls for researchers to avoid. Throughout, we illustrate our points with examples from a simulated social system. Our aim is to provide social network researchers with a deeper understanding of analytical approaches to enhance their confidence when tailoring reference models to specific research questions.     

Genetics of somatic mammalian cells. IX. Quantitation of mutagenesis by physical and chemical agents

The system previously described for inducing single gene mutations in Chinese hamster cells has been extended to produce additional auxotrophic mutants. An improved method for quantitating the efficiency of single gene mutation to specific auxotrophies has been developed. Mutagenesis in the forward direction has been measured after treatment of these cells with ethyl methanesulfonate, N-methyl-N¹-nitro-N-nitrosoguanidine, hydroxylamine, an acridine mustard (ICR-191), caffeine and ultraviolet- and X-irradiation. For each agent, the single cell survival curve and the efficiency of chromatid breakage and rearrangement were measured. Similar measurements were also carried out with a water-soluble carcinogen N-nitrosomethylurea, which was shown to be effective in producing auxotrophic, somatic mutations. These results offer promise of illuminating the relationships between cell killing, chromosomal aberration, single gene mutations and carcinogenesis produced by various agents. The methods described can be used in routine testing of drugs, food additives, and environmental pollutants for mutagenic action in mammalian cells in vitro.