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In humans, variation of the ATP7A gene may cause cranial exostosis, which is similar to “human horn,” but the function of the ATP7A gene in sheep is still unknown. Tissue expression patterns and potential functional loci analysis of the ATP7A gene could help understand its function in sheep horn. In this study, we first identified tissue, sex, breed, and species-specific expression of the ATP7A gene in sheep based on the RNA-sequencing (RNA-seq) data. Second, the potential functional sites of the ATP7A gene were analyzed by using the whole genome sequencing (WGS) data of 99 sheep from 10 breeds. Last, the allele-specific expression of the ATP7A gene was explored. Our result showed the ATP7A gene has significantly higher expression in the big horn than in the small horn, and the ATP7A gene has high expression in the horn and skin, suggesting that this gene may be related to the horn. The PCA results show that the region around the ATP7A can distinguish horned and hornless groups to some extent, further indicating that the ATP7A may be related to horns. When compared with other species, we find seven ruminate specific amino acid sites of the ATP7A protein, which can be important to the ruminate horn. By analyzing WGS, we found 6 SNP sites with significant differences in frequency in horned and hornless populations, and most of these variants are present in the intron. But we still find some potential functional sites, including three missenses, three synonymous mutations, and four Indels. Finally, by combining the RNA-seq and WGS functional loci results, we find three mutations that showed allele-specific expression between big and small horns. This study shows that the ATP7A gene in sheep may be related to horn size, and several potential functional sites we identified here can be useful molecular markers for sheep horn breeding.

Previous studies have screened key candidate genes for litter size in sheep, including fibrillin-1 (FBN1), family with sequence similarity 184 member B (FAM184B) and zinc finger and AT-hook domain containing (ZFAT). Therefore, it is necessary to verify these genes in the Xinggao mutton sheep population and determine the associated loci for litter size. In this study, three loci (FBN1 g.160338382 T > C, FAM184B g.398531673 C > T and ZFAT g.20150315 C > T) were firstly screened based on the population differentiation coefficient between the polytocous and monotocous sheep groups. Then, population genetic analysis and association analysis were performed on these loci. The results revealed that the g.160338382 T > C in FBN1 was significantly associated with the litter size of sheep. Moreover, there was no significant interaction effect between the g.160338382 T > C locus and FecB on litter size. Notably, g.160338382 T > C is adjacent to the anterior border of exon 58 and belongs to a splice polypyrimidine tract variant, which may lead to alternative splicing and ultimately cause changes in the structure and function of the protein. In summary, our results provided a potentially effective genetic marker for improving the litter size of sheep.

Abstract Background Sheep have developed the ability to store fat in their tails, which is a unique way of reserving energy to survive a harsh environment. However, the mechanism underlying this adaptive trait remains largely unsolved. Results In the present study, we provide evidence for the genetic determinants of fat tails, based on whole genome sequences of 89 individual sheep. A genome-wide scan of selective sweep identified several candidate loci including a region at chromosome 13, a haplotype of which underwent rapid evolution and spread through fat-tailed populations in China and the Middle East. Sequence analysis revealed an inter-genic origin of this locus, which later became a hotspot of ruminant-specific retro-transposon named BovB. Additionally, the candidate locus was validated based on a fat- and thin-tailed cross population. The expression of an upstream gene BMP2 was differentially regulated between fat-tailed and thin-tailed individuals in tail adipose and several other tissue types. Conclusions Our findings suggest the fixation of fat tails in domestic sheep is caused by a selective sweep near a retro-transposable hotspot at chromosome 13, the diversity of which specifically affects the expression of BMP2. The present study has shed light onto the understanding of fat metabolism.

Background: Animal domestication has been extensively studied, but the process of feralization remains poorly understood. Results: Here, we performed whole-genome sequencing of 99 sheep and identified a primary genetic divergence between 2 heterogeneous populations in the Tibetan Plateau, including 1 semi-feral lineage. Selective sweep and candidate gene analysis revealed local adaptations of these sheep associated with sensory perception, muscle strength, eating habit, mating process, and aggressive behavior. In particular, a horn-related gene, RXFP2, showed signs of rapid evolution specifically in the semi-feral breeds. A unique haplotype and repressed horn-related tissue expression of RXFP2 were correlated with higher horn length, as well as spiral and horizontally extended horn shape. Conclusions: Semi-feralization has an extensive impact on diverse phenotypic traits of sheep. By acquiring features like those of their wild ancestors, semi-feral sheep were able to regain fitness while in frequent contact with wild surroundings and rare human interventions. This study provides a new insight into the evolution of domestic animals when human interventions are no longer dominant. [ABSTRACT FROM AUTHOR]

DIO2 was studied as a candidate gene for reproduction in sheep. Three pairs of primers were designed to detect single nucleotide polymorphisms (SNPs) of exon 2 of DIO2 in nonseasonal and seasonal reproduction breeds. The polymorphisms were detected using SeqMan II and analyzed by PCR-RFLP. The sheep DIO2 gene was cloned and its mutations were detected in five sheep breeds whose reproductive seasonality and litter sizes were different. Association analyses were performed to reveal the relationships between SNPs and reproductive seasonality as well as litter size in sheep. The results showed that a 1041-bp DNA fragment of the sheep DIO2 gene was obtained and a part of the coding sequence of 591 bp encodes 196 amino acids, having high homology with that of other mammals. Moreover, three mutations (G318T, G482C, and C885T) were detected. The test of genotype distribution in five sheep breeds showed that there were significant differences between nonseasonal and seasonal breeds for 318 and 482 loci. However, the associations between the three polymorphisms and sheep seasonal reproduction were not very distinct. Additionally, there was no significant associations between polymorphisms and litter sizes in Small Tail Han sheep. These results may provide the basic theory for further study. [ABSTRACT FROM AUTHOR]

The aims of study were to reveal the changes in genetic diversity in reproduction selection of sheep. Genetic polymorphisms of microsatellite GC101 locus and its linkage with the FecB gene were detected in Chinese local sheep (Small Tail Han and Hu sheep) and western sheep (Texel and Dorset) breeds. There was the same FecB mutation (A746G) in both Small Tail Han and Hu sheep as that in Booroola Merino ewes, but not in Texel and Dorset sheep. Seven alleles, from 192 bp to 210 bp, and 20 genotypes were detected at the GC101 locus in 447 individuals totally. The preponderant allele was 200 bp for Chinese sheep and 202 bp for western sheep. Linkage analysis showed that there was strong linkage disequilibrium between the 200-bp allele of the GC101 locus and the B allele of the FecB gene (r² = 0.639). These results preliminarily implied that both the 200-bp allele of the GC101 locus and the B allele of FecB had been reinforced in reproduction selection of Chinese sheep. The differentiation of GC101 allele distribution between Chinese sheep and western sheep also indicated that the FecB of Chinese sheep might be derived from Chinese local areas. [ABSTRACT FROM AUTHOR]

The existence of major genes affecting fecundity in sheep flocks throughout the world has been demonstrated. Three major genes whose mutations can increase ovulation rate have been discovered, and all related to the transforming growth factor β (TGF-β) superfamily. The mutant FecB of bone morphogenetic protein receptor 1B (BMPR1B) has an additive effect on ovulation rate. Six mutations (FecXI, FecXH, FecXG, FecXB, FecXL, FecXR) of bone morphogenetic protein 15 (BMP15) related with fertility have been identified that share the same mechanism. All the mutants can increase ovulation rate in heterozygotes and cause complete sterility in homozygotes. Homozygous ewes with two new mutations (FecXGr, FecXO) of BMP15 had increased ovulation rate without causing sterility. There are five mutations in growth differentiation factor 9 (GDF9) associated with sheep prolificacy where FecGE and FecGF have additive an effect on ovulation rate and litter size. The newly identified β-1,4-N-acetylgalactosaminyltransferase 2 (B4GALNT2) gene of FecL is proposed as a new mechanism of ovulation rate regulation in sheep. Woodlands is an X-linked maternally imprinted gene which increases ovulation rate. In addition, several putative major genes need to be verified. This review is focused on the identification of the mutations and mechanisms whereby the major genes affecting ovulation rate.