We developed a quantitative PCR method featuring a reusable single-cell cDNA library immobilized on beads for measuring the expression of multiple genes in a single cell. We used this method to analyze multiple cDNA targets (from several copies to several hundred thousand copies) with an experimental error of 15.9% or less. This method is sufficiently accurate to investigate the heterogeneity of single cells.
A very simple and highly sensitive capillary array gel electrophoresis system is constructed to analyze DNA fragments. On-column detection of DNA migration in a large number of gel-filled capillaries is carried out using side-entry laser irradiation and with a CCD camera, although it has been considered impossible because the irradiation laser is scattered strongly at the surfaces of the first few capillaries. By optimizing optical conditions, the laser beam can be focused repeatedly to irradiate all the capillaries held on a plate by working each capillary as a cylindrical convex lens. DNA sequencing samples migrating in 24 capillaries can simultaneously be analyzed with the system.
A new method for SNP analysis based on the detection of pyrophosphate (PPi) is demonstrated, which is capable of detecting small allele frequency differences between two DNA pools for genetic association studies other than SNP typing. The method is based on specific primer extension reactions coupled with PPi detection. As the specificity of the primer-directed extension is not enough for quantitative SNP analysis, artificial mismatched bases are introduced into the 3′-terminal regions of the specific primers as a way of improving the switching characteristics of the primer extension reactions. The best position in the primer for such artificial mismatched bases is the third position from the primer 3′-terminus. Contamination with endogenous PPi, which produces a large background signal level in SNP analysis, was removed using PPase to degrade the PPi during the sample preparation process. It is possible to accurately and quantitatively analyze SNPs using a set of primers that correspond to the wild-type and mutant DNA segments. The termini of these primers are at the mutation positions. Various types of SNPs were successfully analyzed. It was possible to very accurately determine SNPs with frequencies as low 0.02. It is very reproducible and the allele frequency difference can be determined. It is accurate enough to detect meaningful genetic differences among pooled DNA samples. The method is sensitive enough to detect 14 amol ssM13 DNA. The proposed method seems very promising in terms of realizing a cost-effective, large-scale human genetic testing system.
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