Measurement of single-cell gene expression using capillary electrophoresis

Capillary electrophoresis with laser-induced fluorescence detection was used to monitor gene expression in individual mammalian cells using the reverse transcriptase-polymerase chain reaction. Specifically, beta -actin expression in single LNCaP (prostate cancer) cells was measured. A sieving matrix containing hydroxypropyl methyl cellulose was used to effect size-based separation. Ethidium bromide fluorescence of the product DNA was used as the detection scheme and yielded excellent sensitivity. The beta -actin product, resulting from an individual cell lysed by a freeze-thaw method, gave an average signal-to-noise ratio (S/N) of 77 +/- 27 (n = 2). Chemical lysis of a single cell, using a dilute solution of SDS, gave a S/N of 26 +/- 2 (n = 2), roughly 3-fold lower than for freeze-thaw lysis. An initial detection limit (not considering fully optimized conditions) was calculated from an amplified cDNA standard to correspond to a concentration of similar to 133 starting molecules/nL (of beta -actin mRNA).