Differential microRNA expression analysis in blastocysts by whole mount in situ hybridization and reverse...

There is cumulating evidence that microRNAs (miRNAs) are important regulators of pluripotency and differentiation and, hence, of early lineage segregation in embryo development. To unravel the function of specific miRNAs, it is important not only to analyze miRNA expression in the entire blastocyst but also to determine the site and level of expression in the inner cell mass (ICM) versus trophectoderm (TE). A new strategy has been developed for miRNA expression analysis in ICM and TE using two complementary techniques. By whole mount in situ hybridization (WISH), it was visualized that bta-miR-155 is mainly expressed in the ICM. However, WISH does not provide quantitative data on expression differences between the two cell types. By reverse transcription quantitative polymerase chain reaction (RT-qPCR) on ICM and TE isolates taken from single blastocysts with laser capture microdissection (LCM), it was quantified that bta-miR-155 was 50-fold higher expressed in ICM than in TE. The possibility to quantify both miRNAs and messenger RNAs (mRNAs) in LCM samples offers the opportunity to analyze the expression of both miRNAs and potential targets in one sample. This article shows that a combination of WISH with LCM and subsequent RT-qPCR is a robust strategy to qualitatively and quantitatively analyze differential miRNA expression in discrete cell types of a single blastocyst.