Replica plating of cultured mammalian cells

Rapid cloning of mammalian cells with honeycomb cloning plates and nonlethal vital stains

A rapid and technically simple method for cloning both adhesive and nonadhesive mammalian cells is described. The procedure employs (a) honeycomb cloning plates and (b) nonlethal vital stains. Instead of placing cloning rings around colonies, cells are initially seeded at clonal density directly into a plate containing an array of cloning rings (the honeycomb plate). Hence, the time involved in placing cloning rings around colonies is eliminated. Second, clone-containing wells of the honeycomb plate are easily identified by staining plates with the nonlethal vital stains, MTT or INT tetrazolium. Vital staining eliminates the time involved in searching for clones. Last, clones are transferred with a cotton-tipped swab thereby eliminating the time involved in trypsinization of cells. In this fashion, one can pick and transfer clones of substrate adherent mammalian cells at a rate of one clone/10 to 15 s. Thus, mammalian cells can be cloned as rapidly as cloning can be carried out in microbial systems.

Elimination of Mycoplasma orale from the human hepatoma cell line, PLC/PRF/5

We have tried without success to eliminate M. orale from a human hepatoma line, PLC/PRF/5, using five different methods. We report here the successful elimination of the contamination by a modification of the technique of Marcus et al. [1] using 5-bromodeoxy-uridine (BrdU) instead of 5-bromo-uracil (5-BrUra) and light. We believe that this method may prove useful when rare and valuable cell lines carry the more common mycoplasma contaminant M. orale.

Isolation by a replica-plating technique of Chinese hamster temperature-sensitive cell cycle mutants

Isolation of a wide variety of temperature-sensitive (ts) cell cycle mutants in mammalian cells has previously proved to be a very difficult task. The various procedures used for the isolation of such mutants included a mutant enrichment step based on exposure of the cells to the restrictive temperatures in order to kill the growing wild-type cells with agents that kill DNA-synthesizing cells. Hence, these methods favored the isolation of ts mutants that do not lose viability rapidly at the restrictive temperatures. We have treated cells of the Chinese hamster established cell line E36 with the mutagen ethyl-methane-sulfonate (EMS) and used a replicating technique that we developed to screen the ts mutants for growth. This technique enabled us to recover all its mutants for growth including the ts cell cycle mutants. Screening of the ts cell cycle mutants among the ts mutants for growth was performed by the flow microfluorimetry technique and the premature chromosome condensation technique. Our results show that 1.3% of the survivors of the mutagenic treatment are ts mutants for growth. Six of 84 ts mutants analyzed were found to be ts cell cycle mutants. They include ts mutants arrested in phases G1, S, and G2. Many of the ts mutants for growth including the ts cell cycle mutants arrested in S and G2 lose viability very fast when incubated at the restrictive temperature. As a consequence they could not have been isolated by any method that includes a mutant enrichment step based on the exposure of the cells to the restrictive temperature.