The callipyge mutation enhances the expression of coregulated imprinted genes in cis without affecting their imprinting status

The callipyge (CLPG) phenotype (from kappa alpha lambda iota, "beautiful," and pi iota gamma epsilon, "buttocks") described in sheep is an inherited m uscular hypertrophy that is subject to unusual parent-of-origin effect refe rred to as polar overdominance:only heterozygous individuals having inherit ed the CLPG mutation from their sire exhibit muscular hypertrophy(1). The c allipyge (clpg) locus was mapped to a segment of approximately 400 kb (refs , 2-4), which was shown to contain genes (DLK1, GTL2, PEG11 and MEG8) that are preferentially expressed in skeletal muscle and subject to parental imp rinting in this tissue(5-9). Here we describe effect of the CLPG mutation o n the expression of these four genes, and demonstrate that callipyge indivi duals have a unique expression profile that may for the observed polar over dominance. for the observed polar overdominance.