Estimates of total imprint number withstand transcriptome test

The number of transcripts where allelic bias is dependent parent-of-origin was predicted at 100-200 until two recent studies applied RNA-Seq to brain regions from reciprocally crossed inbred mouse strains and identified over a thousand novel imprinted loci, including hundreds present in only males or females. Reanalysis revealed that the vast majority of these novel loci are explained by technical and biological variation of the approach, and are not genuine cases of general or sex-specific parent-of-origin allelic expression. Independent replication projects that, at most, a few dozen novel imprinted transcripts are present in the dataset, in line with previous projections of 100-200 total imprinted transcripts. Overall design: Whole brain transcriptome analysis of E17.5 F1 embryos from reciprocally crossed C57BL/6J and CastEi/J parents