The mouse insulin-like growth factor type-2 receptor is imprinted and closely linked to the Tme locus

T-ASSOCIATED maternal effect (Tme) is the only known maternal-effect mutation in the mouse^1,2. The defect is nuclear-encoded³ and embryos that inherit a deletion of the Tme locus from their mother die at day 15 of gestation⁴. There are many genomically imprinted regions known in the mouse genome^5,6, but so far no imprinted genes have been cloned. The Tme locus is absent in two chromosome-17 deletion mutants, T^hp and the t^Lub2 and its position has been localized using these deletions to a 1-cM region^7-10. We report here that the genes for insulin-like growth factor type-2 receptor (Igf 2r) and mitochondrial superoxide dismutase-2 (Sod-2) are absent from both deletions. Probes for these genes and for plasminogen (Pig) and T-complex peptide 1 (Tcp-1) were used in pulsed-field gel mapping to show that Tme must lie within a region of 800-1,100 kb. We also demonstrate that embryos express Igf2r only from the maternal chromosome, and that Tcp-1, Pig and Sod-2 are expressed from both chromosomes. Therefore Igf2r is imprinted and closely linked or identical toTme.