An Extended Domain of Kcnq1ot1 Silencing Revealed by an Imprinted Fluorescent Reporter

The distal region of mouse chromosome 7 contains two imprinted domains separated by a relatively gene-poor interval. We have previously described a transgenic mouse line called Tel7KI, which contains a green fluorescent protein (GFP) reporter inserted 2.6 kb upstream of theIns2 gene at the proximal end of this interval. The GFP reporter from Tel7KI is imprinted and maternally expressed in postimplantation embryos. Here, we present evidence that the distal imprinting center, KvDMR1 (IC2), is responsible for the paternal silencing of Tel7KI. First, we show that Tel7KI is silenced when the noncoding RNAKcnq1ot1 is biallelically expressed due to absence of maternal DNA methylation at IC2. Second, we use an embryonic stem (ES) cell differentiation assay to examine the effect of an IC2 deletion incis to Tel7KI and show that it impairs the ability of the paternal transmission Tel7KI ES cells to silence GFP. These results suggested thatKcnq1ot1 silencing extends nearly 300 kb further than previously reported and led us to examine other transcripts between IC1 and IC2. We found that splice variants ofTh andIns2 are imprinted, maternally expressed, and regulated by IC2, showing that the silencing domain uncovered by our transgenic line also affects endogenous transcripts.