Tissue- and developmental stage-specific imprinting of the mouse proinsulin gene, Ins2

We have investigated the imprinting status of two insulin genes using an interspecific recombinant congenic mouse strain carrying Ins1 and Ins2 alleles from Mus spretus on a C57BL/6 genetic background. At Days 12.5, 13.5, and 14.5 of gestation, expression of both parental alleles of both Ins1 and Ins2 was detected in the bodies of the embryos. In the heads, only Ins2 expression was detected, and, again, both parental alleles were expressed. In yolk sacs, only Ins2 transcripts were found. Both parental alleles were expressed on Day 12.5, but the expression of the maternal allele gradually declined with only the paternal allele remaining active by Day 14.5. Thus, Ins2 is subject to genomic imprinting in the yolk sac. This imprinting is not only tissue-specific, but appears to be a multistep process with postzygotic events likely to play an important role in repression of the maternal allele.