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 sizebased 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 ~133 starting molecules/nL (of beta-actin mRNA).