T. L. Shay

Polar overdominance at the ovine callipyge locus

An inheritable muscular hypertrophy was recently described in sheep and shown to be determined by the callipyge gene mapped to ovine chromosome 18. Here, the callipyge phenotype was found to be characterized by a nonmendelian inheritance pattern, referred to as polar overdominance, where only heterozygous individuals having inherited the callipyge mutation from their sire express the phenotype. The possible role of parental imprinting in the determinism of polar overdominance is envisaged.

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

The callipyge (CLPG) phenotype (from καλι, “beautiful,” and πιγɛ, “buttocks”) described in sheep is an inherited muscular hypertrophy that is subject to an unusual parent-of-origin effect referred to as polar overdominance: only heterozygous individuals having inherited the CLPG mutation from their sire exhibit the muscular hypertrophy. The callipyge (clpg) locus was mapped to a chromosome segment of approximately 400 kb (refs. 2–4), which was shown to contain four genes (DLK1, GTL2, PEG11 and MEG8) that are preferentially expressed in skeletal muscle and subject to parental imprinting in this tissue. Here we describe the effect of the CLPG mutation on the expression of these four genes, and demonstrate that callipyge individuals have a unique expression profile that may account for the observed polar overdominance.

Localization of the locus causing Spider Lamb Syndrome to the distal end of ovine Chromosome 6

Abstract. Spider Lamb Syndrome (SLS) is a semi-lethal congenital disorder, causing severe skeletal abnormalities in sheep. The syndrome has now been disseminated into several sheep breeds in the United States, Canada, and Australia. The mode of inheritance for SLS is autosomal recessive, making the identification and culling of carrier animals difficult due to their normal phenotype. Two large pedigrees segregating for the SLS mutation were established, and a genome scan with genetic markers from previously published genome maps of cattle and sheep was used to map the locus causing SLS. Genetic linkage between SLS and several microsatellite markers, OarJMP8, McM214, OarJMP12, and BL1038, was detected, thereby mapping the SLS locus to the telomeric end of ovine Chromosome (Chr) 6. Alignment of ovine Chr 6 with its evolutionary ortholog, human Chr 4, revealed a positional candidate gene, fibroblast growth factor receptor 3 (FGFR3).

Fine-mapping and construction of a bovine contig spanning the ovine callipyge locus

Abstract. The callipyge (CLPG) gene was fine-mapped by linkage analysis to a 4.6-cM chromosome interval on distal ovine OAR18q, flanked by microsatellite markers IDVGA30 and OY3. The OAR18q linkage map and human HSA14q transcript map were aligned by genotyping two bovine-hamster whole-genome radiation hybrid panels with the microsatellite markers, as well as with sequences corresponding to HSA14q genes. Using Type I loci mapping to the IDVGA30–OY3 interval as anchor points, we have constructed a 1.4-Mb bovine BAC contig containing the IDVGA30–OY3 interval. We demonstrate that the IDVGA30– OY3 interval spans approximately 770 kb and contains at least four genes: YY1, WARS, DLK1, and GTL2.

Breakpoint mapping positions the callipyge gene within a 450-kilobase chromosome segment containing the DLK1 and GTL2 genes.

We have previously mapped the ovine callipyge (CLPG) gene,causing a muscular hypertrophy with parent-of-origin-dependentexpression referred to as polar overdominance, to a 4.6-cM chro-mosome interval on distal OAR18q flanked by microsatellitesIDVGA30 and OY3 (Cockett et al. 1996; Shay et al. 2000). BACcontigs spanning this interval were constructed by using bovine(Shay et al. 2000) and subsequently ovine (Segers et al. 2000)reagents. We herein report the isolation of eight novel microsat-ellite markers from these contigs, yielding a marker density of onemicrosatellite per 68 kilobases and the use of these novel markersto position the CLPG gene by breakpoint analysis within a ≈450-kilobase chromosome segment.Five BAC clones jointly spanning most of the IDVGA30–OY3interval were selected from the ovine BAC contig (BACs: 724D11,239G7, 218E10, 497C1, 265F11). BAC DNA was digested tocompletion with three four-cutters yielding blunt-ended restrictionfragments (AluI, HaeIII, and RsaI) used either separately or com-bined. Restriction fragments containing microsatellites were de-tected by standard Southern blotting and hybridization with a(CA)

Polymorphic distribution of the ovine prion protein (PrP) gene in scrapie-infected sheep flocks in which embryo transfer was used to circumvent the transmissions of scrapie.

The genetic sequence of the ovine prion protein (PrP) gene between codons 102 and 175 with emphasis on ovine PrP gene codons 136 and 171 was determined, and the polymorphic distribution of the ovine PrP gene in the scrapie-exposed Suffolk embryo donors and offspring from these donors that were transferred to scrapie-free recipient ewes was investigated in this study. The most common genotype was AA(136)QQ(171) (70% and 63% in the donor and offspring flocks, respectively), which is considered a high risk genotype in US Suffolk sheep. Although embryos were collected from scrapie-positive donors and many embryos had the high risk genotype, no scrapie occurred in the resulting offspring. Based upon the results of this study, we conclude that vertical transmission of scrapie can be circumvented using embryo transfer procedures even when the offspring have the high risk genotype.

The Callipyge gene of sheep

Abstract The callipyge locus is characterized by a novel form of nonmendelian inheritance, referred to as polar overdominance. Acquiring a molecular understanding of this novel biological phenomenon will contribute to the understanding of complex traits, including those in the human. The proposed strategy to clone the callipyge gene is one of positional candidate cloning. This strategy aims at exploiting (a) the available human transcript map, and (b) the remarkable conservation of genome organization amongst mammals, thereby allowing us to apply the advances of the Human Genome Initiative to the ovine species.