Nucleotide Sequence of a 28-kb Mouse Genomic Region Comprising the Imprinted Igf2 Gene

The mouse insulin-like growth factor II gene (Igf2) is physicallylinked to the insulin II gene (Ins2) and both are subject totissue-specific genomic imprinting. The paternal-specific expressionof Igf2 has been associated with hypermethylation of some CpGsites in the 5' flanking region and in the body of the gene.As a first step in analyzing the structural features of thisimprinted locus, we here report the complete nucleotide sequenceof Igf2, including all introns and the intergenic region adjacentto Ins2. This 28-kb segment of mouse chromosome 7 exhibits 80%overall identity with the corresponding rat sequence and hasa high GC content of 52%. In addition to the known CpG islandwithin the second Igf2 promoter, another island was identifiedapproximately 2 kb 5' to the first exon. Other features of thislocus include a 35-fold tandem repeat of an 11-bp sequence thatoverlaps Igf2 pseudo-exon 2, and a B2 repeat element in theintergenic region between Ins2 and Igf2. The GC-richness andthe presence of CpG islands associated with tandem repeats arecommon features of imprinted genes and thus may play a rolein the imprinting mechanism.