Whole-mount MeFISH: a novel technique for simultaneous visualization of specific DNA methylation and protein/RNA...

To understand the spatiotemporal changes in cellular status that occur during embryonic development, it is desirable to detect simultaneously the expression of genes, proteins, and epigenetic modifications in individual embryonic cells. A technique termed methylation-specific fluorescence in situ hybridization (MeFISH) was developed recently that can visualize the methylation status of specific DNA sequences in cells fixed on a glass slide. Here, we adapted this glass slide-based MeFISH to the study of intact embryos, and established a method called whole-mount MeFISH. This method can be applied to any DNA sequences in theory and, as a proof-of-concept experiment, we examined the DNA methylation status of satellite repeats in developing mouse primordial germ cells, in which global DNA demethylation is known to take place, and obtained a result that was consistent with previous findings, thus validating the MeFISH method. We also succeeded in combining whole-mount MeFISH with immunostaining or RNA fluorescence in situ hybridization (RNA-FISH) techniques by adopting steps to retain signals of RNA-FISH or immunostaining after harsh denaturation step of MeFISH. The combined methods enabled the simultaneous visualization of DNA methylation and protein or RNA expression at single-cell resolution without destroying embryonic and nuclear structures. This whole-mount MeFISH technique should facilitate the study of the dynamics of DNA methylation status during embryonic development with unprecedented resolution.