Fig. 1

RNA and successive DNA FISH of imprinted IGF2 locus in porcine fetal liver cells. Nuclei are counterstained with 4′,6′ diamidino-2-phenylindole (DAPI, blue). a, IGF2 RNA FISH: monoallelic expression of IGF2 (one spot labeled in green per nucleus) is detected when non-denatured nuclei are hybridized with a direct Alexa488 labeled IGF2 probe. The monoallelic pattern was detected in six nuclei. Bar = 5 μm; b, IGF2 and H19 RNA FISH: monoallelic expression of IGF2 (one spot labeled in green with dUTP-Alexa488) and H19 (one spot labeled in red with dUTP-Alexa568). IGF2 and H19 RNAs were distant from each other, corresponding to the transcripts of single expressed allele from opposite chromosome 2; c, IGF2 RNA FISH: IGF2 RNA signal was enhanced and stabilized by the use of TSA kit (Biotin - TSA - Alexa488 label); d, Sequential IGF2 RNA-DNA FISH: IGF2 RNA was labeled with a Biotin-TSA-Alexa488 probe (one green spot) and IGF2 DNA with a direct Alexa568-labeled BAC probe (2 spots in red). The RNA signal tags the expressed allele. Bar = 2 μm