Optimization of real time RT-PCR methods for the analysis of gene expression in mouse eggs and preimplantation embryos.

This study was carried out to optimize conditions for using real time RT-PCR as an efficient and precise quantitative method for estimating the transcript levels of genes expressed in samples containing miniscule amounts of RNA, such as single mammalian oocytes and embryos. First, using mouse eggs and blastocysts, we tested three kinds of RNA isolation or collection methods: TRIZOL reagent, oligo-dT conjugated beads, or three freeze/thaw cycles with the reverse transcription buffer. There were no significant differences among three groups in mRNA quantity as assayed by real time RT-PCR analysis. Second, we compared the efficacy of real time analysis between TaqMan fluorescent probes and the SYBR-green dye system. The two systems presented similar real time RT-PCR profiles for the 16s ribosomal protein gene from oocytes to blastocysts. Third, RNA from mouse embryos at defined stages of preimplantation development were isolated and the levels of transcripts encoded by several housekeeping genes (GAPDH, beta-actin, ribosomal protein L7, 16s ribosomal protein, histone H2A.Z) were quantitatively analyzed by real time RT-PCR. The histone H2A.Z and 16s ribosomal protein slightly increased from the egg to blastocyst stages by approximately 10- and 30-fold, respectively. However, other transcripts increased more than 300-fold as a function of developmental stage from eggs to blastocysts. Our results suggest that the simple freezing/thawing method for RNA collection, the economic SYBR-green dye system, and histone H2A.Z gene as an internal control should be useful for the real time RT-PCR analysis of single mouse eggs and preimplantation embryos.