A model of a shared enhancer for p57KIP2 and LIT1 centromeric to BWSCR1 and LIT1. If the enhancer were centromeric to LIT1, then it would activate p57KIP2 when an insulator between p57KIP2 and LIT1 is unmethylated, and it would not be affected by the BWSCR1 chromosomal rearrangements. The same enhancer would activate LIT1 when the insulator was methylated. Note that the precise location of the enhancer is immaterial as long as it is centromeric to LIT1. E, enhancer (green); I, insulator (red); maternally expressed p57KIP2 and H19 (pink); paternally expressed LIT1 and IGF2 (blue); cen, toward the centromere; tel, toward the telomere. Arrows indicate alternate use of the enhancer.