Gene analysis techniques最新文献

The ability to create targeted mutations in the mouse will have an impact on many areas of research in mammalian biology. Mutations are generated in embryonic stem (ES) cells by homologous recombination between exogenously added DNA and the endogenous chromosomal sequences. These cells are then used to generate chimeric intermediates that pass the mutant allele through the germ line, initiating a strain of mice that carry the desired mutation. This review focuses on the selection of a starting ES cell line, introduction of DNA into ES cells, construction of gene targeting vectors, and selection/enrichment schemes for the isolation of targeted cell lines. The generation of mice that carry the targeted allele is briefly outlined.

A solution hybridization method for the quantification of specific mRNAs is described. This assay utilizes complementary RNA probes prepared by in vitro transcription, sandwich hybridization in solution, and affinity-based hybrid collection. The possibility of using this method for crude biological samples without purifying mRNAs makes it ideal when accurate quantification of multiple samples is needed. Human N-myc oncogene transcript was used as a model and as little as 0.24 pg (2 × 10⁵ molecules) of N-myc mRNA could be detected. Using this assay it was shown that human neuroblastoma IMR-32 cells contain ′500 N-myc mRNA molecules per cell having a half-life of ′35 min.

In order to develop a short-term, in vivo assay to study the mutagenic effects of chemical exposure, transgenic mice were generated using a lambda shuttle vector containing a lacZ target gene. Following exposure to mutagens, this target can be rescued efficiently from genomic DNA prepared from tissues of the treated mice using restriction minus, in vitro lambda phage packaging extract and restriction minus Escherichia coli plating cultures. Mutations in the target gene appear as colorless plaques on a background of blue plaques when plated on indicator agar. Spontaneous background levels were ′1 × 10⁻⁵ in each of three mouse lineages analyzed. Exposure of lambda transgenic mice to N-ethyl-N-nitrosourea resulted in as much as a 14-fold induction in detected mutations over background levels. The assay is currently being modified to incorporate lacI as the target for ease of mutation detection as well as in vivo excision properties of the Lambda ZAP vector, facilitating sequence analysis of mutant plaques.

A rapid procedure for the isolation of intact total cellular RNA from cultured cells is described. This method combines the simultaneous disruption of cells and extraction of nucleic acids in a single step with the use of phenol and a buffer containing 100 mM LiCl. Total cellular RNA can be isolated in approximately 2 hours. The yield and quality of the RNA is comparable to the more widely employed methods requiring extensive preparatory steps such as extraction using guanidinium thiocyanate and subsequent CsCl gradient centrifugation. The RNA isolated using our procedure contains transcripts up to 10 kb in length and is suitable for Northern analysis. This procedure also yields high-molecular-weight DNA, which is a suitable substrate for restriction endonucleases.

Poly(A) messenger RNA is generally purified from total RNA using oligo(dT) cellulose affinity chromatography or centrifugation through spin columns. We present a new method for rapid purification of poly(A) mRNA using oligo(dT) probes attached to superparamagnetic beads. By magnetic separation, washing, and elution, pure mRNA is obtained from living cells within 10 minutes. This procedure works for crude RNA preparations or cell lysates that would otherwise clog standard oligo(dT) cellulose column systems. The present method reduces the risk of degradation, is highly efficient, and can easily be scaled up or down.